limedServices Tschmica I irm, Up. NOTICE: WHEN GOVERNMENT OR OTHER DRAWINGS, SPECIFICATIONS OR OTHER DATA IMrUID FOR ANY PURPOSE OTHER THAN IN CONNECTION WITH A DEFINITELY RELATE GOVERNMENT PROCUREMENT OPERATION, THE U. S. GOVERNMENT THEREBY INCURS NO RESPONSIBILITY, NOR ANY OBLIGATION WHATSOEVER; AND THE FACT THAT THE GOVERNMENT MAY HAVE FORMULATED, FURNISHED, OR IN ANY WAY SUPPLIED THE SAID DRAWINGS, SPECIFICATIONS, OR OTHER DATA 18 NOT TO BE REGARDED BY IMPLICATION OR OTHERWISE AS IN ANY MANNER LICENSING THE HOLDER OR ANY OTHER. PERSON OR CORPORATION, OR CONVEYING ANY RIGH TS OR PERMSIONII TO MANUFACTUM USE OR SELL ANY PATENTED INVENTION THAT MAY IN ANY WAY BE RELATED THERETO. Reproduced by DOCUMENT SERVICE CENTER KO T BILIR6, BATTON, 2, 0O1 JiC 'NLASSIFIED~
Transcript
limedServices Tschmica I irm, Up.
NOTICE: WHEN GOVERNMENT OR OTHER DRAWINGS, SPECIFICATIONS OR OTHER DATAIMrUID FOR ANY PURPOSE OTHER THAN IN CONNECTION WITH A DEFINITELY RELATE
GOVERNMENT PROCUREMENT OPERATION, THE U. S. GOVERNMENT THEREBY INCURSNO RESPONSIBILITY, NOR ANY OBLIGATION WHATSOEVER; AND THE FACT THAT THEGOVERNMENT MAY HAVE FORMULATED, FURNISHED, OR IN ANY WAY SUPPLIED THESAID DRAWINGS, SPECIFICATIONS, OR OTHER DATA 18 NOT TO BE REGARDED BYIMPLICATION OR OTHERWISE AS IN ANY MANNER LICENSING THE HOLDER OR ANY OTHER.PERSON OR CORPORATION, OR CONVEYING ANY RIGH TS OR PERMSIONII TO MANUFACTUMUSE OR SELL ANY PATENTED INVENTION THAT MAY IN ANY WAY BE RELATED THERETO.
Reproduced byDOCUMENT SERVICE CENTER
KO T BILIR6, BATTON, 2, 0O1
JiC 'NLASSIFIED~
AFCRC Technical Report 53-28
GEOPHYSICAL RESEARCH PAPERS
No. 23LUJ
H - FORECASTING RELATIONSHIPS BETWEEN
-. UPPER LEVEL FLOW AND SURFACE
METEOROLOGICAL PROCESSES
J. J. GEORGE
R. D. ROCHE P. W. FUNKE
H. B. VISSCHER W. R. BIGGERS
R. J. SHAFER R. M. WHITNG
AUGUST 1953
Geophysics Research Directorate
Air Force Cambridge Research Center
Air Research and Development Command
BestAvailable
Copy
AFCRC Technical Report 53-28
GEOPHYSICAL RESEARCH PAPERS
No. 23
FORECASTING RELATIONSHIPS BETWEEN
UPPER LEVEL FLOW AND SURFACE
METEOROLOGICAL PROCESSES
J. J. GEORGE
R. D. ROCHE P. W. FUNKE
H. B. VISSCHER W. R. BIGGERS
R. P. SHAFER R. M. WHITING
AUGUST 1953
Geophysics Research Directorate
Air Force Cambridge Research Center
Cambridge, Massachusetts
I 'iiiiri.vi nthol'. of practical forcatf iiig are ilt-igned andi de% eloped for ij~e in the foilol4 ing: the
predicttion of co, iogene-i- in the eatern lo rt ion of Ilte I. ittd Sta tes. applicable to No arin ct"oolovie, tril. the
Prediction of t rat k. peed anti fit Itre intenit ) fi r 4 rtaini la-'e. oft cu' lonec. aireadov. eallilibed; the teed
anui tra, k of tolil ant ie' I one, w. r thlit entire I itel ,tatr and miuthern ( 'anala: autid the 2 I-hour future
pt~iition of cold front ooo er tlie I luted Sta te" east oif Iii he ooie .
Cla~ification of cocloiie lid- been matde accoring to [lit- tdirection of pa-t ito'.ettient andi the direc-
tion ot(f t le upptI er ctirren1 t~ alo'. e Ile '. tione. ( 'old front1 a re d i' iIItIi it' t'- .INo categorie* ateortlingi to)
their orientIat ion: eat-N%c-tI IN ptv. are fuirthI er tuI i di N ile vd atcordIinw to ItIhu area in Ns~ Iu titiIIit-'. are locate d.
%lI finai foreea~ting tliagrani, hou. the di~trilittion of data li-ut1 to ton~triltt themn. ., .- ntialh all
15 1. 1 3rd line Delete 'which also indicates location of eachcyclone in the data sample for Category Icyclones.
In CYCLOGENESIS Section:
34 1. 5 para. 3 Change "Fig. 10" to"Fig. 13."
37 Fig. 15 legend-line 6 Should read "(Fig. 16) as zero unless..."
50 4. line 4 after "p. 29" add "and p. 33."
50 6. Change "east" to read "E. S. T.
50 1 1. line 3 Change "east' to read "E. S. T."
In CATEGORY I CYCLONE Section:
51 1. 1 let para. After "winter season. " add "An example ofthis type low is shown in Fig. l(a)."
60 Before "STAGE I" insert "Fig. 38."60 Before "STAGE II" insert "Fig. 39."61 Before "COMPOSITE GRAPH" insert "Fig.40."
61 Legend Delete "open circles with etc. " and change to
read "N represents cyclones which did not filletc." Delete "filled circles with etc. " andchange to read "numerals represent fillingcyclones and number of hours till filling."
61 Legend - Stage 2 Add "700 mb AMPLITUDE - the maximumlatitude difference of the contour over the lowfrom the ridge west to the trough east."
65 2. 1st line Delete "X" in the 850 column and place justbefore "24" so as to read ". . . . X 24 ."
70 Line 5 Change "Section 1.34" to read "Section 1.33."
75 1st para. line 3 Delete "and 62."
75 lot para. line 3 Remove paren after "Fig. 39" and place at endof sentence.
George, J. J., R. D. Roche, H. B. Vischer, R. J. Shaler, '. W. Funke, W. R. Bigges, and Rt. M. Whiting (August 1953),
"Forecasting Relationships Betwees Upper level Flow and Surface Meteorological Processes," Geophysical ResearchPapers No. 23, Geophysics Research Directorate, Casmridge, Massachusetts.
Page No. Section Errata
78 Within box that begins "If curved anticyclonically etc.," change"p. 30" to read "p. 69."
TI'i pI gwtr Fire~nI ' I Iit- rc-tilt I f ttnI ii N1t vard- of Iiltcliga Iioin bII i grliili p of Fa~tern tir I Jne.' lnett)r-
(etqiic Hii clwaerli It )irvitoraitt of t kir Fotrce ( :izlfridge lktetartl Cen~ter, %ir Rtemwarch all( I )evelop-mntnt Cil iiiiniz. .and %,v atrt aizi l I prI thug o*ltlioni- tot ttiii imiittrtdilt ptroblemi, of Ahitrt-raznge Ieather
foreca- 11 ng. The qita tti IN prgre.- report - of I hin 1 rtjtt'I inicatedl that practical andi tthjectile soluitions8
lice' living otainzed. Ilive'. re-tilt., thotigh ini ome1 rv- 1 wct- incomlette and miirtliiietl %4ere immediately
tinefil it) the -hlort-raiwe forecaster.
)uil iizijed di-tribtttin %a, madi~ e of the titarterllt rt'hxrt*,adl 'titn the demand for copie, far exceed]ed
the' muiluuer adl ade. Thki hOalw' 4.l~1, Nrt tell to tonili~tdatt antd to make thle remilts of the inlestigations
motrge ntralhi adl ajle. It 1 i piilitd. lIto il er, fttr techiclial iriformnatiotz tunlN allti dotes not represent
'ill vt i n- tof thet papter reiet t I lit. , i 1 tjl of the fttreca~ter; alil elemcnt' tif the solutins are easily
inved'.tll 't dot- it.i~ltin amn for'tdIinlg offite. 'Ihletrt'tical (ttns'ithtratitili jila~ ed a piart in definuing tile
,tralegl of the .ttt- k, but the fr't~ing ridet- glten aret ttmple~elk e'mpiirical and Acere, 14ithout excepion,
It Nitv ,aittI of 1 datrewt r amter, -r( iO~tl htt'iii'~ the tiltr~itN otf the foeatn rb
it'ii~ ut' ~ t ii, -itlijit Lii t t houigh .itttcliqwt lit'rt' maieito Itt-tabi~i cotmitmn ttxls for forecasting.
In ati nh r vli Nwh ithi Ili' tl'm of the' fort-tt'lr. all t'tittn o1f lt 1talsr tdteal ba-iallN %i1 -lifter'
%lltitn t~tr thet I jittI tlt 'I b hl a atd 'd lt' l%t'rt roniniti to thet mitnhi. of Noleilber throuLgh March.
Ie~t. Hot t lt(4tii l14111f. Iot dttttrmniit' ft'e ,ipphctilijt. tt other montith., nor tt tter areas.
'I I& jpijen bold not lot, t'tzi-trtthd~ it tttomleitte iiii"14r tot the Narittls prttgntici piroblems1. It it;
loih i l. ittIr.thait iteC frt'a zii g dt itt- de-criht'd Aill resuilt in a mvalitiarabulc increase in the accuracy
tif hort-ranugte iitathetr prict ion.
7
Tle~ Page
Abs.tract . 3
F'orewordI .............. . 5
IntrodulIction . 15 .................. i
TIhe P~rediction of ( clogenesis . 21
(.ategories I and I1 CNvlones .* 51R. 1). RochZe an(I 11. B. Vissclwr
100. Preliminary Prediction I East.Coast Wedge-Front . I . 18
1o1. Final Prediction of Speed for Eas~t Coast Wedge-Front . . .1') .....
FORECASTING RELATIONSHIPS BETWEENUPPER LEVEL FLOW AND SURFACE
METEOROLOGICAL PROCESSES
INT'RODI UC TIO N
F~ronti its inception. t his re-search Iia- had as its- goal tilt ie!.tigationl of oliject i i forecasting methods
neves a rN to the prep a rationIi of siho rt -range jiri gnoi . o-sf thet d14111i flalt Rile tiro-icialIs it eins ii r mally-
found on a surface iseather chart. ); ithi a %ici to later integration of theitlbotls into, a standard pro.
cedltre for preparation of a short -range str face progno-tiv chbart, t hi- re-earci has been- 54-Jiarate(Iintoinde-
Twndent sections: the imest igatiiin of tilte prorue-s of c~ clogene!,is: th it- decloijiilent and nioi einent of cv-
clones; the zioi ement of antici clines: and thet liehaiior of cold front-..
At the start of this studli it %s apparent that there %sere -.ei ral baiahdfeet~ t.%x of c. clones.
Thei differences %sere bes t remoliegi bi uidillg, tile- ,c lonet- inlto four categoriv- out-pending 1 s0n tisocriteria:
thle past track of thet cd-l. and tilt, direction of tbe li aloft oi er thet cell. D ifferent foreviiw ng eiols
%ere de% eloped for each iategori ofc c- ilone.. Sice Yie.irki all ,i clone- diealt isitli in tihis sttili %sere %sarmones, thet atllir- didl not attempt ito classif, c' clones into iarmu or cold t~ pes*
1. 1. C:ATEGORtY I (;YL(t IN
. t egor,. I ci .e-b aret, lho ie d i at lia,.- btee i oii ing friom tie ni rt iiisest quadranIt and are- 10ua ted
beneath nortisest Ibis at 71)1 mnlo. G;.nciraull tilt, fis is (wclrring init a hrojil belt isith no sensibole dejiar-
tures front thet patte-rn ini tilt- %itnit'. of thle litis cell. % v e~aiplc i- -ii,% ni ini Fig,. I (u). is iichi also indicates
the Ii t-a ti in of each ci cilone in thet dlata samplj e fo~r ( :a t egor I c% cli iI s.
1.2. (:A'rEGORlY 11 (2 ION LS
Categovi It cvI, cli- are, those that hai e bteen nioi ing fronti thet nirs-st ijiadrant anl( are locatedundr i u hi istii ii 14 t s i- It isi -uIied b% a perl-tiurba tio n ill a ha sica II ni rt i is st conltour p~a ttern.
Figure 1(b) illus trates this tNI p.
1.3. C IK(H II;CA)E
:Cteg~or% Ill ci iliiuiis art- those that cont inuie intiing front thet nortli'.est quadratt although licated
tinder sotit Ii% i-t fitit at 7 ))) tit i Ilii- to t e ireseiwe of it majo r t rough I t thtItat Ics e~l. Figure I (c depicts a
t~ iical tipper air piattern isith at (ategori IIl (-' ilime.
iiu--s I*6 and (c) iniicate ceirtain aaui1 litiili si-astirviints (if tit(- uiwer air c-ontour piatte-rn. tilese
furoiolvIi an liiijec tiie iii-t In of dei-term11iin g islie t I r th 11-4ri gh i is a perlitirba t iin (or at muajor t rough. Refer
to) page 80 fi r 41etails o f iis methodl.
&lanuicrpt rceived for pubzlication 7 Novertmbrr 19?52.
Ito
500
3*,,~ ~ rM 53,2 IS!
17
00
'ASFL 0 j&
400
30070 0 in b
IIDEC 19148 1 0 E
Fig. I (c). Exam ple of typical ' W-mb circulation pattern amweiated with Category III C&ACS (effective trough). In this case,a is 4 ; a, 25 and aj 13'.
5c)
400
SFC
LOW
H
-30*
?-OJAN- 1951 1100 H
Fig.l(d). Example of ly pical 7W-mb circulation pa ttern wowiated wi thC Ntegorv TV Cal-Aet.
lx
1.4. CATEGORY IV CYCLONES
(ategori IN' c,.clones are those that have been moving from the southwest quadrant and are located
beiieath soutimest lhm aloft. Figure I(d) shows a t.spical pattern.
It is important that the forecaster be familiar with this cyclone classification because the initial step in
forecasting the behavior of any cyclone is to place it into one of these four categories. llhwever, not all
cyclones can be so classified; an occasional cyclone moving out of the northwest, for example, and located
immediately under a 700 nib trough cannot be identified with either a belt of northwest flow or southwest
flow. Also, a few surface systems with predominantly west-to-east flow aloft cannot be included in the
categories. No treatment of these types has so far been undertaken by this project.
Although cyclones in Categories I through IV make their initial appearance in western North America,all lows which originate from cyclogenetic processes in the eastern United States almost invariably are born
in Category IV. Nevertheless. these four categories of cyclones are not always independent of each other
but are frequently time-related. A cyclone under northwest flow moving from the northwest may pass
successively through Categories II and III, and thence to Category IV. It is not always possible to trace
this development. Once the cyclone leaves Category I, the development maN be so rapid that an upper
air chart taken 12 hours later will show the cclone as Category IV. There is evidence, however, to support
the belief that many cyclones follow a life cycle through all four categories.
1.5. INTENSITY MEASUREMENT OF CYCLONES
Since the inception of this research, there has been considerable discussion of intensity measurements.
Since deepening and filling are to be predicted through the use of objective tools, it is imperative that
quantitative anti objective measurements of intensity be obtained. The traditional use of central pressure
as a gage of intensity has been abandoned because for certain types of cyclones central pressure falls con-
currently with a decrease in the cyclonic circulation. Several other measurements have been discarded for
similar reasons.
Since cvclonic circulation is being discussed, it appears that the most desirable gage of intensity will beone which is a measure of the strength of this circulation, namely, the pressure gradient. A prime requisite
for comparison of intensities of numerous cclones is that the circulation of these lows be measured over a
standard area. The method f(,r determining the intensity which has been developed in this study defines
this area as a circle of 60) miles radius, using as a center the center of s, mmetrl of the inner isobars of the
cyclone. The objective procedure is to measure the pressure differences in millibars between the center ofthe cyclone and the four cardinal directions at points 60)0 miles from this center. The average pressure
difference is then computed, and this average difference is defined as the intensit*" count of the low. These
counts vary from 2 to 40, with the average intensity near 14. There will be occasional measurements in
which the 600-mile distance will exceed the distance to a ridge line. In these cases, only the maximum pres-
sure difference is to be used.
There are, of course, weaknesses in the method, but after considerable trial this appears to be the most
satisfactory objective measure of cyclonic circulation.
1.6. MEASUREMENTS AND DATA
The methods to be described consider surface pressure systems only at 0130E and 1330F and upper-
level charts at 1000E and 2200E. The 3-hour time lag between the upper-level data and the surface data
.T.
/ gl Il d H. (Ii)V 4 V 1II"I
ha~ s. ee i ncorpobrat ed into all f ireva .ting pa ramie t ers. so that int erpol~a tion (of pressure s ~ tern posit ions is
Unt't'ssarv . The starting time of all forecasts is the time of the surface synoptic data, 01I31- and 1330E.
In all measurements of geostrop~hic % intl. the staiidarl geost rophic windscale should be ulsed (without
correct ion for curi attire). When contour heighit differences %ecre mieasured, it %a- found cmpI~iricahll. neces-
sarN to apllbI correction~s. multipdking In the proper latitude factor listed boehl%
In thle piract ical appllica tion (of these forecasting methods, the meteorologist must mneasure many of tilepiarameter,- onl a % eat her mall, and smcasjmiaII in different tinit... Thel( use oIf properly graduated ruller'
facilitates these mleasujrements.. lsIn ine sect on.. of tbi. repo~rt. the delineation of specific areas is essential;
this can best be accomplished lo. the uise of a templlate or oi erla% . Figure 2 illustrates an overlay, com-
bining linear measuring ruler, in different unitl * alinlar mea-urcments, geostrophic wind scales, and areadelineatioai templates; this (J'b rla% ma he bholograplled and enlargedl to the scale of any1 Lambert conformal
conic map.
All of the basic research data has locen obtained froin the malI files of Eastern Air Lines. Inc. Allcharts have been labeled using [astern standard time. 'I'he( geograjdiical limits of thle base chart include
the North American continent, em-ltadina laska and ( :anada north oi(f the (17thl parallel, but including thleCaribbean Islands. Thle projection is Larniert conformal conic %~it h standard parallels at 250 and 48'30'.
The scale of the base surface map is I:,1iK).and of thle- tipper-le-iel chart 1: 15JO),M)N.
21
JOSEPH1 J. G;EORGt(E
1.1. INTh&WtCTION
Tihe deri~ at i n an tip rodu ction oi f thle I' IlrgI tIial dra l' anl' e Tat rE hid I c1co i. e 'xtretiiel v comnplex.[rhere can be lit tle doubt. 11(14 11er, that %4hen two air mlasse's of different dlens'ities are brought into juxta-position at the same altitude, the potential energ is favorable to the formation of new cyclones. It there-fore follows that indications of this kind oif cvulogencsis should be soutght at levels where- both cold andwarm air niasses exist. Since cold mnasses are relatively shallow in the eastern United States, attentionshouldl be focused (in tile lowest stand~ardI level above the surface, that is. 8,-(0 ni. Although the data in thisstudyv havye bleen gathered for higher levels, the results empha.size that ('vclogenesis in the eastern UnitedStates can best bew predicted front the conditions4 met at thle 85(t-iit Ie', .. Indeed, for the particular geo-graphic area involked, in all but a few c'ases. it I-an apparenti be Im done only' from the 850-mb level. Thereis a fundamental difference between thle ci-clones born in thl-e astern United States and those in certaitnother regions, notablN tue Mediterranean atil southwest United States. T[he formner are almost invariablywarm and shallow at birth. w4hereas the latter are prellloninantl.N cold deepI low . Methods of forecastingthe formation (If cold low s hia~e nolt been attemiptedl in this paper.
Even if the colnclulsioln that thle predlictiont (If warmi cNlo~(gl'til.is must be accomplflishedi with referenceonly toI low levelis is %alill, iz doeHs not nec-essaril' N follow that till act ual pressure- redluct ion in-(lived is eon-tributed entirely, or indeed, in large parts. lii the( low h-.e, p] rocesses. It i riot a s'ubject iibich will bepursued here, the tiiil Illjecti~ 11(f thlis pae is tol (li-tl'rllie lllla15 (If forecastinig ('I (llgl'nl'sis regardless ofthe physical proc'esses 14hitit produce it.
ToI (late. till ,,eo1grap~lv a rea in 14111 i ('I Ill IglnI' is [it- a -i b c t adied liai ( Im-e conllfitned toI tile latitudesof the Unite'd Statl's ietwcenl lonigitud~eS ( atll 1(H)'~ 'I'hlc (ffe('til(*tlls (If tihl method for forecasting
c- elogenesis described in this rlmsrt. lie's ifl tile recolgntion b%11il till forecaster lofre~rtain platterns in tile tipper
level ('harts, It is concl''eed that11 sub~jectivity is itil~l'l in till reco(gnition (of a pat tern, nevertheless, theparticutlar pattern p)re'edlinlg ('clogenesis is quite %ell delfjined andl esiwcialk for really significant edco-genesis, c'an hlarly lx' mistake'n.
In discussing metelolh(gical platternis, illustrations are itifinitel', tmore' effective than descriptions.Tile presentation (If a tnumtbler (If actual examle~ls shldl qu1i1klv acqutaitnt tile reader with the appearanceof tile patterns so tilat tiaeN becomle l'atilv recognizable . Ac'cordingly, this sectiotn wAill conlttain a mlaxiltutfl
of illustrations.
TIhe patterns,. although nolt tidlll sensitive, reqluire tllat as nmuch care lbe c'~er('isedl hy thle analyst indrawing isotherms as a (careful melteolroloIgist gives Ill till plac'ing oIf contours. Not all analysts, byv anymeans, are in the hlabit o~f placing this muc(h enhlasis oII iso~thermis; and attemlpts to use charts whichhave not bee'n checkedl for accuaracyv may well lead tol unnecessary e'rro~rs.
Thle data for tis study 'onisistedl lofthe winter monlthtis (If Nlvetiber. Decemiber, January, Februaryand March for tile four winters from 1947- 48 tharotugh 19(50 5I. lit thlat periodl. 258 caset hlistorifes, includ-ing negative cases, were coIllec'tedl anlI studIied. Eastern standard titme is used throughout. These dataare included in Appendix 1.
)*01
\ \Ix
1/0. /
Fig. 3. The lIA-it- ifep fiwt.,r- at.ili ml, niti-A. ini jreictiiig, % irm ii izem ili,-rat-i. 'Ie lit-iI air iiijetii i-
clearl i taLim 1 iave -%er F- hIih i Iic m-it cnnni.i l-waiti..ii. it 1lwati 'lif then iwi. cmvIn i literrminwd hire a-
'in then line lmi-eI -i~ in.. . i. iunf.. Or-h,iim.riki. tiiiming ".mili Iw, f(r f-wiiatimii I H i,,iirn aftr thin ;attm'rn ii, tinr,,t .b.1
Th, d. Ie ima-ic -lirmi-tinm i n whwi the. mne. -mni -lmmilnl -tarl zi giin thi .lw amraig, ,I the (emw~ rive~itititmi .if the ii.-
ttbmn .inniilni -limikmn .irrm .in im ~ vmitnmiir. triple. -imikrdniv r,1 . irtm mi ml 'n %n mn~e o~f time,. tm~i vinnitn i' a,~ ail-
minim. Im1w trunk muir% -a.ii-tva.irdi I niiue thin .implittid,-.- tC iii -~mtlwin-n iin. Iii. -1 ..m.. I pairametersu arc: (1) the greate~tt-mpm~,r.tuur.- gr nit mi dIt, iwnrthviv*t i-Inirmit miwan.im frmim t lic nImnt i tim. l.-' w n.itiin .uiit lIm miii.. oftie predicted1-m-atmi w hich %il ii Itic grmemt-.t gradint. It I-. immniiicitn lutre a%. .11. ,_ \ nmrt--nIim t-~ tin inmemi the geoinitrophic windin tihe ...,uthmit inurreit mie-t 4f the preiniteni lnintin if * uumngin-nrn h i t i' mllii-trutmni thughiii kiaiiam and (;emrgia.)A Iuin the ..nuuherimi-im-t nmnir Iulin-K .nmaiiu~d tie triugh Ii imiirthi ifi the piniirinn i ingnInimi.iniiation. noi geiaitrophic wind isinwm-ir-i and time -1pn. 1. tin 111, . inn. 6-i f,menmt a.i-"I .mi ph. 11, .1'*ranzi %. imni iti thu.. inujetin Ins ahinut 25 knots and theilieruinl ringe k. .iiiit 16 oi r 17I
1.2. THlE FOR)IECASING P; I'A'-rlN
With ver~ '1 . few eeptioins. evern sigiicant case ofn c'm clogcnesis whIich occturred in the Untited States
and adjacent waters east of 950 longi itide (luring thec test jeriod w4as porece-ded bk a com it n pattern at 350
nib. A~t somte point along the isontermt ribbon (the blit of packed isothertns). a current b-conies ti.tabtlisltt'i
which at most is usually onkI a few hutndred miles wide and] In Ich ob,.ionislv crosses thten isoinithriti ribiboin
front cold to warmi air. Such a cuirrent is ustialli assolciated with an uplier trough atid is tflol~t effectji c. in]
23
7 37 AVERAGE NO OF HOURS
BETWEEN INJECTION ANDCYCLOGENESIS FOR
7 VARIOUS LATITUDESLATITUDE AV NO HRS
55 43.27 50 40 5
45 35 540 24 335 20 0
500" 30 19.0
6
3 6
4 40#
. . .8 5 3 94 3 0
S3333O0 2 3 g/
1100 3 54 4 ?
4 43A 344j3 1 4 3 4
2 2 2 4 3 4 4~
3 3
4 4 4 O 30 43 30 40 40
43 33 3 23 44 3
4 4 4 4 -ao3 STArUTE MIES
3
Fig. 4. rhe location of centers of injection. Each figure is located at renter of injection and repreoento a number of 6.hourintervals between the time the injection wai first established and the apewarance, of the first close isobar of the related cyclo-genesis.
causing cyclogenesis under the following conditions: when the isotherm ribbon is well to the south of 3WO;when the number of isotherms cronsed by the current is large; and when the current is of appreciable strength
i.e., greater than 15 knots. The current is usually best delineated by actual wind reports rather than con.tours, because at times there is a great deal of crosscontour flow. Figure 3 shows the typical pattern.
At first it %4ill ajipear that the I4Wt-1)l of ai cen'1ter ofcl 4,1 air injec(tion~ is ifiliviilt anid -I
111051 cass thIe're is reinark alii'. little e'iia 1144 for e'rror. I hiih 4' ex Jriencl' with iita , t- A -,I i " I"-
(In this p4)1111. Thet l)cation of this enlter is iniltolrtallt because Io) a large t'xt114 it g, .,, It-
formation of the new esclone.
D~etermfining the tillie %he a)11 new ci ' 14)clone1%ill formi, is of primne iniportuno v'. 'I It, -W
will henceforth he called a cold air injectimi.' begint& front 12 to .18 liours biefore Owi hro i I. ......I
gen~esis apitears and fromt 71W it) N) i4 n iles uofitreant fromt the regioni of 'ci ' ', I I
inter% al is 18 hours. an4 IN ths alue i- used in mnaking forecasts. Since thle rippe.r-4r .iii! I
12-hour intervals, each case' lna, 1w in error hIt at least prlus or minus 6 hours. lit 14i lis.d I -
six hotirly windl soundings mia- be used4 to) check the beginning of the cold air 1up, 611. f..
should be forecast to occur 18 liours later.
Figure 4 is a map showing the geo)graplhical loc'atio~n of the centers of injec t , fr
cases and shows clearly that the najoriti of 4411 injections take place at Ooutherh .it .1 .
found that the latitude of injection is related to the timne interval between injr,,iio . idfollows: the interval decreatss with dec'4reasing latitnde. Cases where a new center bIrrii
tenior of a well developed cyclone and msequen4a'rtl.% hecane tile onli c'enter are .111 4, 1"
Must be treated separately and are not 'ie, it in 1 .I
A cold air injection is. of course. nolthing 1more4 nor less than apparent cold air .fthtaking place as a current rather than as a broadi scaJle phlenoimenon. When the i-i-t lit!-
ovrperhaps a thousand miles and there doe'- nl4t 4'xi~t a par1kinlg or ali imohtrnsi ild-ri i If,,
cyclogenesis are not usually present, even though biroad scale cold11 advection is per-.
frijettions frequently are amisociated with suirface % clmlic. Ainel. of 4'olrse. %it il'l~nt(4llrs and isllie4rnis are ouit (f phlase'. iThe dllcl' till '.tirface 1,,. tug' iilr4 lik, 1% '- .
injlct it fit. hutt a~s % ill ill' noltedla lter. t his 11111'S not nill'4 ltiml v%' cl.ogctift-' nmti- net, - . I
tainll. 'I fil- Ni ind I in Ln tsit- a%4'1agedl m v4r til str'Lllllinlg is cl'led'l thll a% 'rage % i1111: it -dit, 1- '.1'h% 4-t itnate- so that inore ilnilllrtanll' is Llsnignll if) fire 14n hich r1kbtro-t' fire' elnorI cl(-vi, p., L I -Ill, rll-.
T'he center (of injection lie-, in thle iddle of tire strongest liwrtilon (If tlle crosil-isoltllrr 4.i iifl -I) Ii,.
Nrl ol Is ' a k re-r-o * norho 61.7Oinain r efu rmtemrda ers
tit?~~ ~ ~ ~ ~ /-1' .io n0 ln otePt,4qetIfhu oiin h rcwr aeb1,1. Iix be ')tMarIA ,1 w atua ceterof njetio ineac ca , oieningthepoit mrke
"Iait - lt &m orle Adtacn te1-hu rakoftecyln w ih a reiulybe
I,,~ ~ ~ tiK4Arl ,, r O ufc hrs 1(custefrcse ilb ne h opl
-wt ff'- .I~ tt %I.,,1wia ic ewilnthveti nor ainb tetm e ae i
fllIJII III ltl 14. t.IC ilhespotee y aalte t sso n ntes iuesm rl
1600 300
1400,
080
AI900
Fig. 6. The tracks of primary cyclones which underwent cen ter j omps. Practically all of them are between 610 and 104' inorientation. (They are measureti the same a those in Fig. 5.) The roughly circular area outlinca the 18.hour position ofnearly all the primary center, following which the jump occurredl.
27
Fig. 7. The truckA of primary q'yclonem having trarks4 greater than W'~ and which are aaaociated with c) dogenesis. Comparewith Fig. 6. Note the few trarkm which have an 18-hour position within the crtolt jump circle. The group of storms at thebottom art! sqparated from center jump~ cases by their tracks which are greater than 10 &and aim) most of them are filling storms.
The situation for a series of weak shortlived waves is accompanied by a very slow movement of thecenter of injection (less than 200 miles in 12 hours), while an intensify ing cyclone has an associated center ofInjection which travels usually in a southeasterly direction more rapidly.
'hen an injection occurs, one of three things almost invariably follows: the parent cyclone deepens;a new cyclone forms; or a center jump occurs. Probably the most difficult problem for the forecaster tosolve is deciding which of these three alternatives will occur. Methods will be described which will enablethe decision to be made with reasonable objectivity and accuracy, but there are cases which cause difficulty,
as will be shown.
A brief discussion of definitions used in this section is necessary. The term cycopenesis refers to anyclosed isobar forming around lower pressure where none existed before. The term secondary cvlone meanscyclogenesis occurring near, and in relation to, a primary cyclone. Obviously, cyclogenesis applies to bothsecondary cyclones and new storms formed without relation to any other. A center jump is considered tobe a special tN pe of cyclogenesis and sometimes is indistinguishable from secondary cyclogenesis occurringnear the center of an existing storm. The usual means of differentiation used in this paper is as follows:when the two centers are present, there should he a minimum of 3 mb pressure difference between the oldcenter of low pressure anti the col separating new and old centers for the case to be classified as a secondarycyclone. Usually, too, when a new center forms on a warn front it is classified at a secondary regardlessof other considerations. In most cases, there will be little difficulty in labeling each case properly. Itshould be remembered, however, that there appears to be a continuous transition zone between secondariesand center jumps. When it is difficult to tell them apart, the forecast will be similar.
When an injection is first established, anti a well develnped cyclonic circulation is associated with it,the most immediate problem is to determine if a center jump will occur. This requires a determination ofthe future course and speed of the c.clone, and is best done by the methods given elsewhere in this paper.At any rate, the 18.hour future position of the low center is predicted.
The 18.hour paths of the primary cyclones in two years of the dependent sample of data have beenplotted in Figs. 5, 6. and 7. An increase in the sample would unduly complicate the figures and add little.Figure 5 includes all examples that were associated with cyclogenesis and that had courses less than 610east of north.
All courses were measured from the meridian over the primary storm at the beginning of the track.In each of these graphs, the point of common reference was the center of injection. Figure 6 is a similarplot of the tracks of cyclones that underwent center jumps. Figure 7 is a plot of storm center tracks takenin a similar fashion for all storms associated with new cyclogenesis but with tracks greater than 60* eastfrom north. Note the almost complete separation obtained betveen the 18-hour future position of thecenter jump tracks (Fig. 6) and those storms having similar tracks but with new cyclogenesis associated.The small group of tracks moving southeast at the bottom are practically all on greater courses than thelimiting value of 1040.
From the behavior of the cyclone track illustrated in these three figures, a method can be deduced forpredicting when a center jump will occur and when new cyclogenesis will take place assuming, of course,that an actrate forecast of the 18.hour future position of cyclone centers can be made. All measurementsare made between the initial point and the 18-hour position of the low center.
A study of Fig. 6 leads to the following rule: cyclones that have tracks between 610 and 104" east ofnorth and speeds such that the 18-hour position of the low center is expected to lie within the roughly circulararea of this figure, will be accompanied by center jumps and no other form of cyclogenesis.
29~
1020
UJ1010- -- __ _
-j NEW CYCLOGENESIS
( 00
0 0 0 0
0 0990-
z
ORIGINAL LOW DEEPENS li
u NO NEW CYCLOGENESiS0
0 200 400 800 B00 1000 1200 1400 1600 >1700
DISTANCE FROM CENTER OF INJECTION TO SURFACE LOW CENTER CMILES)
Fig. 8. A methiAl ii caa ~ I i,~I ~iIep.i r i, o,- which are a"'. ate w *lith i(%c~ ,l .dgrne'.ia. The alk%rrpreaientitdiat anucr. niea .urd oi indec hu-t Ie the' re-iihr ftho 1i,% .' at the %tirfai'e and tie ceniter of inject inn at 8544 nit). Thlelow 1.w~ilim is taken % it hi 'iiic',rre,,tu'iii fi, 'iU the 041,311 -ir 1I13111 chiar t iva.1 tit# li e , 4n' tile 8541 .mti chart. O rdina tr, areaim il's thle lnt e-t 4aa-Ice I re.uru' ru-c. inl fo r the I.,%.4 1 ier iiircle are shoiwn0 i the gra ph fori t hn- liiia awhIich were not11'"'Wiaited w iti anli v gui ~ i and. .hits fir ii ne wh i ch were. ii,- ur .eli riratt th Ile t- e. la-cs gii ing 91, percent
accurate delini tion (dlmi.' hut diat a).
In center jum cil~tases. I114 new (center IIstialIN movuies at approiximateki the saine speed as tile old onedid before tite jump occurred-, Iioiever, tite newi center is usualh lolcatedl to tile cast oIf the old otne. Unlesstaken into accoutnt, this factor (,atI-(-* errors it) ciclone speed predictions b~asedl onl 1114)ilent oif tile old(
('enter. After a c'enter junip ol(ijtrs. thle intezisiIN (If a cvclone almost alwai s itncreases markedli, and thereis a distinct tendency for ci 'lotes oif modleratte or deep intensity to follow a irc doically curved track intothe nortb.
Thle concept oif a c'enter junip mai aplpear artificial, however, tile needl for it was dictated bN the datafor the foliowing reasons:
(1) There is a real differenc'e in the contour appearance and the resualting weather between a center
jump and new cyclogenesis.
(2) A center jump tnav, and often does, take plac'e so close to tile original 'etnter that otnly slightalteratio4n will result in tite isobaric' patte'rn. The prediction of locatiotn of thle new center %4illfrequently be ven different tihan if new ('tlogenesis is expected.
(3) We have alread i noted that following thee4stalishtnent of an injection either the parent cyclonedeepens, a new c'*(l(Ine is formed, or a center junip occurs. The nmethod for predicting a ('enter
jump has jutst bwen dlescribled. In any single case, once thle possibility of a center jumip has beeneliminated, there remains the very important tinestin (If which of tile other twol alternatiies will
31)
1020 ,
il
SU IJ I
w1000. -•e....--0 C.I
00
0 0\( 0 0< 0
0 00
LJU 01
UI
970 A .. . . .. . l
0 S200 40 0 600 Boo 1000 1200 1400 1600 > 1700
DISTANCE FROM CENTER OF INJECTION TO SJRFACE LOW CENTER (MILES)
Fig. 9. A trt of the deepening or new rragenrui% %eparation ulawn in Fig. H. 'Tic amc *%mli,,, are -ed. ri'uracv ,ofseparation i6 85 ercent. (Independent dlata.)
take place. The mechanisn by means of which tlte. are separated will he de.m ribed next. It willsuffice here to say that if all center jump cases are not first eliminated, this ncilani-in is ren-
dered useless.
The tracks of deepening cyclones which are not assiciated with new cvclogenesis or center jumps arealmost always less than 61° east of north and a plot f their tracks as slhon in Fig. 5 does not in any waydistinguish them from those which are accompanied by new ciclogenesis.
Accordingly, it has been necessary to seek other fac-tors to determine when such a cold air injectionwill be associated with new cyclogenesis and when it %ill not. Figure 8 shows that the distance betweenthe parent low and the center of cold injection gives a method of division. When the distance is large,new cyclogenesis occurs. The surface central pressure of the parent low and the distance between the sur.face low center and the center of cold air injection are plotted as ordinate and abscissa. No (,enter jumpcases are included. None of the centers are moving between 61 and 104". The division is remarkably goodgiving an over all accuracy for the dependent data of 94 percent. Figure 9 is a similar plot of independenttest data using the winter of 1951-52. Accuracy drops to 85 percent which is still satisfactory.
Using independent data it is not easy to find some objective measure of testing these predictions. Thewinter of 1951-52. comprising 0 cases, was used as an independent check. There are, however, six differentcomponents of the forecast (time, intensity, location, speed, track, type) and there were few cases when theforecast was entirely satisfactory for all of them. Of the 04) cases, the essential development was correctlyforecast 45 times or 75 percent. There were 10 cases (17 per'enl) in which major errors were made but inwhich substantial portiong were also correct. Five complete errors resulted (8 percent) two of which weredue to incomplete data in Mexico.
31
60
t,0 0
80
00
180 170 I60I- IS0
Fig. 14). The I, catic in of ne% cycIlagenetioc ease* re-ferredl ti, a roormon vrt ter of rolil air injection. rhe hearings are determinedlfrom the meridian over the center of injection (marked C r). The diatanme" are 4ealt-4l in otatlite mile,4 from a ILambaert conformalconic projection with standlardi parallel% at,~ anol 111 30'. D~ifference- inscmal' title to time projection have Ieern ignored. Thepolar coiordinatek have beven Fihown tow, enable tile- diagram to lir reproolmced to, any mail wocale. No center jump" have beecnincluded in thisk oample. They oi'eur mainly north of tile 00 tle. The preferred loc-ation for prediction 6~ uAmaally along tilecenter line. In synopmtic practice thme area ip beawt tranikferred in% proper scale to a transpoarency. The center of injection is.placed over the actual center andi the 4M)' radlian where it cropos tile ouiter line of the kiolticv-"hapced area is placedl on the sameparallel. Tme area is then properly aligned.4 antl may lie traced or itmaica td foil tihe a,'tilal chart.
It must be remembered, however, that if toi logenesis is correctly forecast as Io location, the forecast
for 24 to 36 hours is almost certain to be fairly acturate. Any errors in spmeed. direction, or intensity will
only affect the forecast for a later period and presumabl) later information may permit correction of such
errors.
32
HIGH LOW
0
I
0L OW / • •HG
Fig. I1. The 4vnoptic location of new cycogenesis for the mo t usual aynoptic situation at the time of cyvlogenesis. The new
cyclone forma in the north portion of the col or even within the northern low when the front is oriented north-ootl or nearly a.
As the front orientation rotates to northeast-northweat. the new depression tends to form in the middle of the col. and s it
approaches eaAt.west, it forms most often at the extreme southern and western portions.
It is asumed that the methods developed so far enable the forecaster to determine whether or not
cyclogenesis will occur and, if so, the type of cyclogenesis. It now remains to establish methods for fore.
casting the following information concerning new cyclogenesis: location, timing, intensity of development,
track, and speed.
1.3. LOCATION OF NEW CYCLOGENESIS
In Fig. 10 all cases of new cyclogenesis (including center jumps) have been plotted relative to a common
center of cold air injection. The kidney.shaped area encompasses most of the locations. It is used as a
first approximation for the predicted center by placing a transparency of this figure on the 850 mb chart
in proper orientation with the center of injection. The new center will develop within this area. It is
usually preferable to predict the cyclogenesis to take place along the center line which will be called the
%Locus of Cyclogenesis." Methods described below are useful in placing the location along the extent of
this locus.
The location of cyclogenesis in the usual synoptic situation at the time it occurs is shown in Fig. I1.
When the front is oriented north-outh or nearly so, the new ('I clone forms in tie north JIortion of the cL.preven within the northern low. As the frontal orientation rotates to northeast -soth Iest the new depression
tends to form in the middle of the col and as it approaches east- ,est. it forms most often at the extreme
33
101
Fig. 12. The prdieted and actual locations of cyelogene~is. P stands fo predieted, Ffor actual poition of formation. Thenumeral refera to the cane number in Appendiz 1. (Independent data.)
southern and western portions . W hen no parent low is involved, the new storm almost always forms at the
extreme south (of the locus line.
When the isotherm ribbon is packed ciosely, i.e., the gradient is high, the point of cyclogensis is almostalways well south along the locus. Conversely, loosely packed isotherms are associated with northerly
locations. The gradient value for the median case when cyclogenesis takes place due east of the centerof injection is about 150 C per 350 statute miles. As tbe gradient increases, the predicted position should
move southl4ard and as it decreases, northward. This indication is not in conflict with any previouslygiven, for north-.south fronts usually are associated with loosely packed isotherms and east-west fronts with
high south to north thermal gradients.
Center jumps almost always take place in the northern portion of the kidney-shaped area. Gulf
of Mexico depressions which move eastward along the Gulf Coast are exceptions. These nearly always
jump across Florida in a northeast direction and may be in the center or in the southern part of the kidney-
shaped area.
Another aid in determining the location of cyclogenesis within the kidney -shaped area is the temper-ature of the 850 mb surace over the locus of cyclogeneui.. Table 1 gives the median temperatures and
usual ranges. The cyclogenest most often occurs at the intersection of the locus of cyclogenesis and the
* ~ rmedian 850 mh iaothenn.
34
'lale 1. 8(54) nlb lrnjceratur-a over lem, point of r.'ce-,.j,.it takrnat tier tinC.' 44 lirmirtio.
851) melp Trm~eeratiarr Iteceigr
Now. W 5 tip 15
D.ec. 9 5 to 15
~Jan. 5 0 to 13F.'1l. 8 3 to 13Mar. 10 7 to I5
There are occcas'ional instaees depjaring wielie. fronm these- values and tl--are useful only for checkingpurposes~. Center iutip% ujearl ' alisa %s'm'our in parts olf the kielne'i-shaped area where tem~peratures are
much lower than the'se v alues (riengli (0' to - 2(0' Q.
Figure 12 is a mail shove~ing predlictedl and observed lesatiofts of ci * logenesis for tile independent (data.
The reader (,an obtain from it an idlea of itle oirder of act-tirac% obtainable.
1.4. TIMING
Little can be added to the generalities aireadi given on page 24 concerning the timing miechiafini.
Fighteen hours is the most common time lag belicen estabilishment of an injection and tile subsequecnt
cyclogenersis. For injections (entered north if 370 latitude. tilie- first appewaranc'e of the injec'tion is igno~redl
a nd an 18-hour timte lag is ffirecast from tie second coensecu'iee 12-hour mail. This has prove(] the most
satisfactor-, adjustment foer tilie latitude factor. TIhere are mianN times when an injection is borderline.
for exampile. when it ocurs at a very oblique angle on one inap and becomes clear etat on thle next. In such
(ases 6 or 12 hours should bie deducted fromt tile usual 18-hour lag front the se'cond1 map time.
1.5. Ft Tir RE INTENSITY
Throughout the research on this subject, it was found that a correlation existed between the intensity
of the c-old air injection at 8.50 mb and the resulting intensiti* of c (-lone lie% eleiptent. The initial intensity
of tile nascent ci clones depeends mostli upon the vigor of tile 810 nil cold air injection. Shiafer, in another
section of this paper. fecund that older ci clones (Categor% IN") dlepende upon higher level (500 mb) param-
eters for deepening espe'ially when the ciclone is weak. Hlowever. lie found that for strong ciclones of
thio% categeorv, further deepening was best indicated at 850 mbl.
Figure 13 shlows the relationship between thle intensiti of the c-old air injection and the initial c 'ycloner
intensities losing thle count sistrm described in thle introdtuction. The results, front this graph can usually
be improved upon b%1 a subjective correction according to whether the 5MX nil) surface is favorable for
further development.
Figure I4 is a graph similar to Fig. 10; however, the intensities plotted are the maximum attained dur-
ing the 30 hours following thle birth of tie cyclone and the farnil% of -utrves is naturally displaced a little.
It is the first plhase of a mualtipile correlation designed to give future intensity. Figure 15 is the second
phase which takes into account tile trough sharpness and temtperature gradient at the 500 mb level.
Figure 16 is tile final graph plotting thle 5WN nib) results as abscissa anel the 850 mul parameters as ordi-
naters. Major storms are efineel as thopse vdi'h reach an intensit% 'ount of l6 or mnore. Minor stormvs lhave
35
0 ---0 I -
10 15 '20
455
4
" 40. 5 * 1
6... 116 6 10 '20
0
z 5 43(.61 4
j 56 1010
o o10
LiLi
z 4a s . . t" .. ,Io , I4 ,o -, ...4
W 4 ? 4 7 149> 3 6 ' S ° I3IO iicr20~ - - a4 3 3 7-
0 5 10 Is 20 25 30 35 40TEMPERATURE RANGE OF THE INJECTION (OC)
Fig. 13. The initial intensity of new cyclone formation determined by the first plateau of intensity values after the new cyclone
forms. If a continual increase in intensity is noted, the first measurable intensity is chosen. The abcissa represents the
temperature range of the optimum streamline through the isotherm ribbon. The ordinate values are the average wind speed
along the optimum streamline weighted by eye according to the intensity of thermal gradient in each section. The family of
curves is labeled in intensity scale values for the initial strength of the new cyclone.
counts of less than 16 btt tsuall front 8 to U. Fillers, of course. disappear. Frequency of distribution
of the three storm classes is indicated in the appropriate areas and the graph is obviously a valuable fore-
casting tool. All data for this graph were taken from the prediction charts approximately 18 hours prior
to the appearance of the first closed isobar.
1.6. TilE FUTURE TRACK
The initial estimate of the track of the resulting storms is chosen as the mean between the steepest
portion of the eastern troughs of isothertms anti height 'o.totars just cstl of the cold air injection at the time
3t,
45 - . ___
510 15
I.-I0 40 4 It Is---tz
Z_ C 1S 15 HIGHEST VALUE USED 3
zI0 35 - ZO a
W 21 0 113
X 0 14-J4-4-1 3 12 -0 4 1 - _________
l'- 6 14 14 5
014 4 ii 0t
125 1*ZIs7? 140 3 i is eit 12isezo____ _ _ _
ll.1 N 15 I Is N1 &i 3I 410Is1 0 4
IS
Ij- -3 _-11 3 - 0 0-i
W 3 3 1 I
104 1010
4
TEMPERATURE RANGE OF THE INJECTION COC)404
Fig. It1 The fir~t stagf- a4 muile colrreIlatio~n techiquiiwil for .ri-afating the niazimum intenAity in new cyclogenetic catief.The figurrs mi~teredI arc the maximumi intriuiijee l, hc nr% c'.cIonr in the firitt 36 hugre of its eliptenve (54 hours from foreottime). 'The tempeorature range anl average hind speedI %cre d~escribed in the legend for Fig. 13.
when jireii lioii c~an lx- tinafeI (I'] bun . liglorI 31 coitillin- aii ihisatraiio'i (i hovi these are chosct. Thlis
dlirection is I Ilien iit rree leil iii accoiehenve ul li 1hle re I Ii tliihi l lpre-,e i Fii g. I17. Thlere' are 4wieasiona Ilarge deIEarhitr frlltt forretast valites of Ilii -1E'ei. N% lien tihe itnilitlde tof the isotliertn. is less than 1o0
Eflf tiidte Iliroligli tilE' Erller Elf eili iitjtE-iE6t. hIlE' I EIEIEE d iov %ill tiialh eon.' top it coEulrse Elf l,.t to .astlitlint 21 hipitr- E'~ i' if itk iiil EiiirE is iiledrl milier~.'I
Thie -liv'ed olf 1 I le i tc ElliE i. rie tedo Iotiheii WIiI-iih Ii,'rmiaI grailii'hl 1t its n~orthlivet and liia rejire-seniiiial 810-ili %iliel .EEiovvl it1i IIe av bluetli C/ atui lit#' lewaii Elf v~lo-mss Figuare 18 expjressestis reIattnen-liiijhiIErival . The. re..idlt Eifa loi opf the. itiei'iiln ii au sa~mple for Iiotli iitial track aid
16
14-
13
12to . 20
C 2f
.10 *
9 14. tool
5 15 *15
7 14C C, 0 2 26, t2 -
6. * 13
e \ 2
.4
10
4. 4
4-~. -
200 400 600 800 1000 1200 t400 1600 1800TROUJGH SHARPNESS IN F E-E AT S;-() B COR4RECTED FOR LATITUDE BY TABLE
Fig. I- 11' li . Aee tage o)f a multiple correlation technitque foor ftorecasiting the maximum intensity of new c~-clernes. These;ear~ieelctr- fro- 1leth eetaineel froom the 54(0-mb chart at the time the preediction is made. The figures pletted arr again themaceedum elte'n~iv (of the rsulting cyclone. Thue circlet] figures refer to filling storms. The tr-ough shar,ee1 iq the sameparrmle-ter en-rl in 4 atcgwyr IV fitr determining deepening. i.e., the height elifference in feet between the trouigh line and a point10111 miles ca., plus the same measurement 101M) miles went, all taken at the latitude of predicted cycleegencsip. It hien thetrough i% more than II000 miles from the predicted cyclogrnesis. it is carried to the final ciorrelation graph(Fig. l6 as zero) unilessits extrapeepla led movlemenlt berings its predictedl location within the ltNK).mile range within 24 hours after the time of prediction.The full v alue tof thei parameter isi then used. In mse cases the subsequent sharpening or flattening of troughs isnapparent andimay foe allowed some suobjective weight.
The temperature differeinceso between the trough line at the latitude of predicted cyclogenesis and a point 1000 statute miles,eastward are used so erdinates. The differences are considered positive when the warmer air is at the eastern point. Negativedifferences are shown as zero on the figure.
qocede are' gi en ill Tabeles 2 anti I. It is ealasioti, freeti thlese.. re'sults that the large variations front forecastvalites will lit- e'ncounttered notl infre~lttae'lli. Tis is hiardly~ mirpri-4ing c'onsidering that lite forecast is made140111C 18I lhotmrs before' liti e- Ine is evenl ini exjslene anti the. siltuation contains inie'rentlv large values of
ae'celeraI i il. NeverthIe'le'ss. thewse fore-casting re'lafiunsijs still remlaiti valuale infoermationi anti are supe~rior
to any subjective' method loresetll available.
Oe,,
X Xx X K x
-0 ' TOTAL 434 W MAJOR 88% MAJOR
CYCLONES 7 X MINOR
0 \ THIS 5.FILLERSARE A
- 0 V 0 X• P
0
0.Lcr 00 * 6o a
TOTAL 32} 0 28%/ MAJOR
62. MINOR 0aO Q 50 x OK 9% FILLERSCD VERY SMALL CYCLONES
Fig. 16. The final correlation for predicting mazimum intensity of the new cyclone. The ordinate represents the valuesobtained from the preliminary graph of Fig. 14 and the absiciss represents those obtained from Fig. IS. The three areas areplainly delineated and the suggested forecast for each area is noted therein.
1.8. EXCEPTIONS
1.81. Sperial Category Cydones
Special category cyclones (defined in the section on Category IV cyclones) are always intense, slow
movers. Frequently, at one stage in their history, they move in a direction west of north. Normal fore.
casting methods are not used with these storms; instead, the following rules are utilized. A center jump
almos.t invariabl owcurs and should always he forecast approxinuttely due east of the original center and
C') U..
0 _ _ _ _ _ _ _ _ _ _
zw
z X 0
0
w
0 1
30
0 001 02
FOECS 2A.0TNIY E YLNI g 7 A'r.iwl . . piwII.tw*i~l*lrct'ia tirindf.n h'ereii~n ,c.e'r - iu ~,l~n- II..t-j.~i ncmj 4ii r iem ~~nn. oit~ f
fla ton ig.i 1.. A~e owle 1iie I-eeeeeiii- t.,c ulir tiant irijii f -ett -i -. r, l, iltl~,i
ustia11,% thyi ~caci e c eif a r ti e I a irr% fl gaateInh g a from r i e 48, ilil airr sa .~~cth wiTeflci' ~ a ingii m aaiiw c V Iqmr frc. iiatw ni-i -l e cret a tc 4 16, a l lie iitii in t rni. ii- icil tonge
ri'quiri Mal ui If) ihrcat is ft m h i to 1wlien ne ~ e eh ,rint is thr dr i fi reca im 1 i i cr lte fwajmn
a In cut It PNa ci dar. iii ii tr foc i agtile m f o f the lo i I' v t g1 tie is Ii jeli ofi' t ilu i awe jump io i eon and
frC-afrii'ri'y a refany .deaii il ~len irchitltiill nsinn a tnguale ofcli ain utlw ryclica l ana dusalyitharacot rent o aeiir fe t e am i-ioni-n form thhat, ointal ax ine a n tit o i alrseadyh t~ur
tongiiecaatrsis So ei elcvoe oi at tlpo nt-ntioe n at t imesarayeiting
10
'Table 2. Pre.dice.I initial truck.. d ,f nud .'p4d 4 t eic made" l }mir, l,.f64or' the vqIhn, formp, indrlwndent data.
:-,'rert i s ForecastS:a-' %% crage )ire'hn for F,,rrca.t Actual Mjeed ActualNo. l.oihvrin- and (itIr Interun..ity (i1)rgrr,. frnm North) (11ph)
Table 3. Recapitulation of rable 2.(Percent of Occurrencee)
Error L-e than II 11-20 Over 20
Initial Tradi, . ..... 40 30 30
Spe.l .............. 55 20 25
Both V ithin limits . 27 23 50°
' Either speed or direction missed more than 20 (degrees for direction. mph for speed).
4o50 60~
40 La
40
01 48 50op
65
z60
35 -Q 35 40 -0
OD 3034 36
32z 30 ----- o 3a835 -10 ao 0
§ 420 42 \ 6AO50
252015 0 o A .-
m 2514is2 0 o 4
3 34 )40
20-~V ~ 6 40 ~-
41 r 069q
5 28 3I ..-
30
16 20 t 30 1 34~: OSB30."10o 2220 3.3 30 .3324 o 0( 0 ISI aIa 21 ~~20 'l I.,? b24 21 02 01
0 5s 20 25 30 35 40 45 50 55MAXIMUM TEMPERATURE DIFFERENCE IN NOR'THWEST QUADRANT -C)
Fig.. 18. %. mreip.d f,.r e..timlr n g ti , ., I f O lp ii .. 'p. 'Ii he -. 1 ii umid. at ai refireriulatis.- 1 ..'gt in the '.mpth-
%.-( it o II , pt.pp IllI .... ttr ..fiPiJp .lm aml Oiwp. i .l .- i ~ (~ led ~ ii.-itwi "If.dt.. a, O milr inate. 'lp'I..nit. of tileI.c.-prq,r- pi the l~Ilrirtirr dlplTrv,p nwa~-,pr,,i i6-1 . ip Ow p. I ti. Ow i o-1 f the c~ I.~l-. lifle Within 24m) or
MHO~ miil-' of tIi, iprt-diite p.- itew 4op I lire w p , w-til %ii .ill II, -ip .p ips tplp t,-itleraitar. .1Ipffe.nu, to a1 lwxltt IIH414 vime%iii tipi rwprtiplpt -pip.irant. Ti,, mwpp'i.ppre liesi.i. -inc.. wia4-imll% -al .ip i eri .lI r- ti .iio...ng tie jI..iti.tnof 1 ro-divircs pl,,rnt-i. (WhIichi fre-1 I,.,t i p wcur) nom % nia L. I.,rgo- ,jp fl,.p,.lc,- its Ott- it ,. lpe-ra Iire li fference. All mraireflliltt are takenat 850 ml,. S lien tipe ge'uitr.;lwic win mni nla-pp . Ill "i-li --r It~~. Ir u. iwi tip. -plpprppnp,,.. co.pl r aroupndi tile 8411. , trppghlit1 ntprti ~f gir peuiird jH.-iti..n of vyii ipvrpp-o. a -Iwed ,f 211 nphi I, jpreiird arbiltrarily.
EXPLANATION OF SYMBOLS FOR FIGS. 9 THROUGH 31.
L 998 - PRIMARY LOW CENTRAL PRESSURE 998 MB.
P-HOUR - HOUR AT WHICH PREDICTION CAN BE MADE.
P+15 - Is HOURS AFTER TIME OF PREDICTION.
CENTER OF SECONDARY CYCLONE.
-SYMBOL INDICATING A COLD AIR INJECTION.
-- CENTER OF COLD AIR INJECTION.
"- DIRECTION CHOSEN FOR STEERING FROM ISOTHERMS.
- DIRECTION CHOSEN FOR STEERING FROM CONTOURS.
AT - THE DIFFERENCE IN TEMPERATURE AT 890 MB MEASURED TOWARD COLD AIR FROMTHE PREDICTED POINT OF FORMATION OF THE NEW CYCLONE AND OVER A DISTANCE
OF %=0 MILES,
- ISOTHERMS (5°C INTERVALS).
- CONTOURS (2D0 FT. INTERVALS).
'.. .
I NI'4 l .i : . " .. . .
L%
. ..... If
Fig. 19 A form of upper air pattern apm oieat'l liIlt i(ogrne. ePen in the a-ence of any cold air injection &t 85) nib. Apattern much a thipi pro hably in,,urqe tirmnig i0l.grlini. It In, le prrrnt at any level up to .4(m rul. but need lie prieseuntat only one of them. It %ai faiirl rare. ieerurring vpil a"idl $-i time% in the four vear examined; but in eve'ry va," it wa*RIeoiatlde with a Ptrng eehne. It ip imlprtant net te e'nfumee th. pattern with an 'ordinary S Phajle to the iF4)therm% whichare handled in the ordinary feohion. A lietituct narrow teengueo" elhod air moving at high speed ie neeary.
AA~ A .at
A ' .. / /X- 'kAi
At,,
neci, mtrni h, l~l.%il"0 fru d i m-tS.a r,-i -%-
,,c r . w hrII a icl t '.(jj- lr rlul a r.lg 1,i)' ,1" 1 w 1p, l'it . . w io la~n i a5oi
nIrli~- url
all Ai s. LO H U
2tt. ~ ~ ~ ~ ~ ~ ~ ~ RE S R 1000 Mn,;iinrn.tte B~ti et..~ii.nI , t~n',l nriii nili r. i 's ein.~~nii," eipiett ~h'i tn I.. s nll~- i enns tn jrnnijnl r'n~l inhs ut ~jt. i. innti ena iinne n reni~ne.i tna nnji
tinifinjitit 'U~r'iAt
fitdn
Fig. 2 1. A frequnent piattern thon~ing a doubile injectioen. Thbis tweters wuntallv w.ith lelo cycelnm sshick mtove off tak~ing piththe'm a arcienic inje'e'tio n clomr'. tit th.' ceinte'r litil gradl lyi Ira% ing Ie't ie a t nitiglt lave or te% rip sit int. -t' ci. eli icitils Ciii 'n rd nie.
The elietane beetwneen the, ce'nter tof the sitiri andn * it'i emt Irimtesu cri'tter eef iinjection ptnl tc tIed n'i't)e feli rn i ii.' if reesen'yclegeneea wil! niarciar. Tis maert of ielniecc'nurrence' Ap tie'timen hlilw'ne whie'n twn mattima ofl w itndilme'ilpt are' mienrinti'byn ditstinctly loer valu'e.
I I-- ~t t .i'al r.xmvlp -. HIII-ml- f-r rhart lo-IH 10 Al t%,,m rII,. - Inmg c, Ct-t.l'~ mn itig i- l,rim-. in Gr ,,rg~ia1::; h,ur- iff,.r d , ,1h air iject .,n j apalr 'm' I . ,11. 11,h Jhl it f,rid -hgbhll -,uth Ow lh116111.i' ji hr inlp-vi l.a II,l ni IIhIt Ih Iit- 1|irulric', -1 r n fa rIlh o-r *4 u lhi% dI m- t , 114, 1 ar,. I ' ,1l,11-.
.V,- H O U R - - ... . , N . . ./*- . . a-. - - -
;1100... P+5 4
. ,+ 4 2 ,+ 1•
3 * I
/ -, -i<. I " ."' * ' 4", " .:* ...../ i/ .. .. *
S .,. - ,20 , . ,
Fig. 27. Actual example. 850-mip chart for ItF.14 Novembewr 1947. A w~eak low is fowred near Charlesuton. S~ouath Caro-Iiia, 18 huir" after the Trxap injec'tioun loattern. Note the curing path. the Ilo% amplitude 4u tile iiuitiuurmsu. andl the- niirthurli%location .f the new t rm with respect to th .enter of inject.in.
47
k, S P+3.44/ " / Y b": 7/+- S P 30~I. # -''- . .", / . 7.r ..- ,
Fig. 28. Actual example. 850-mb chart for 2200F, 23 Noember 1947. A center jump case. A primary cyclone, centralpreure of 1005 mb is only 450 miles from center of injection. Note the easterly course of the primary cyclone which is arequirement foe the center jump. Timing is aiout the same on center jump cases as for new cyclogenesi and the action usuallytakes place well north of the latitude of the injection.
~. , i _
N.
L 'N* L 984I.IN.
\ // + '' "' P 24
N .. Nz.. . ,. -]. .*,- ., ', -I .-":'
.5 A f L 992.- **
>"""P- OUR
N' i l A ' / .. 7'G "
/7/
J -
• .. ..- ,.. .." -. 7 .I , ,-,... . . "' a" '
Fig.29. Actualexample. llS0-mh chart for lOF, 7 December 1947. Anegative case. The injection while of excellent defini-tion is only 560 miles from the center of the surface low center which has a central pressure of 992 mb. No cyclogenesis wouldbe predicted except for deepening of the primary low and that is what occurred. Such came usually leave a temporary weakbar metric depression with no bad weather associatdr to the southwest of the center of injection but in this paper these havenot been termed cyclones.
So
,,,P-42 -
,d ., L 0OW -T P :.o '
p -l SP+30 .
~; i-100
25 PH .0..
t - .114 ' IS - . . in'lsloI If -110%. tora Ia'Ia.n faa't...A C, it' it It itia -Ir -a .4 aa -'tm u. 1 1. - to.., ni.. 1ri -, h i,- m 1' ap~a.at., l01411 _')--i 1. inibr N $7ar.. . f lll it# Nri. Y..rL mr 4 sa4Il-Im a f-a-a 4 a it. ,r- ~I thirt %a.1;.rI... i. it,,iiimar ntld Ilafr Iii maII d-t s),,it..rdic q17. aw a a its.0 irah.l. l-. mid .rt.t% % h iI.. ,,%n ilir- s..,a, I, ;,~irtaim t-., ill
, .i-t. it-- pr-.iiii..ii s,r -fT,-,t .. ,i ).. , srL. %mildlla lr .a-it fs-ra,-at it il-. Sills.- IF-r Ii, aasl.- cm d iim ra sls i. .,lu1
1''' N
N. IS _20;_ , 52
- ~ . N -*'* 0
'- CG+*30
--,'NE W STORM DEVELOPS-~.*--- HERE 0730, 26DEC 1947 p1
Fi g. 3!1. A ..ectiqan q.f the 7INmrlp a-hart liar IINIEIE. 25 Dece'mber 1947. '['he a-mali iangur tsp' aainjecitma ilo cla'arly visjle. Ni.inja-tii ..als liaia-arnibla' at ")5( m. but a otimilar a-ll taanpor was appharent at 500 mu. Many anals,.ra ialiawe thar Aaal .ativrmdi--rd~'aa in Fig. 301 mmi ing niart sia..ro anal a-a uaalng tiie anaas aI Newu Y ark, liut a areful checrak 4arn lia Ao that itsa arlill 'ifi-lhlI time- lutl i ndicatedl. laila- an entirely na'w motorm faarmrd A. mhliar a" indicaatred a tvanpor the. Na-u Ysrk Kno... Pl'rllWe"ia pamissabh. from ti, chiart.
stoirms 11m oi tItlit' requiredl piositionl litit in vi tri% ca-* enctinttrvil in tis iriiit..igatiori otit'or theottherha. octcurred. Ilti14 ti r ths ca*t 'a s are ramre. 1 iguirc 0 11) i an rtiiijle tf thu'h t't m p4'f mt imti i tilitiof.
The're % ere t a u I tii-iN of t-ca-itin 4]i11ri I I- I i 1141 l'A 1 ilil Minr uIt'e- It ir ins fo rmretd. pia rticularly alontrgthe cast coiast of the I nlittil States. anid lw'r~isttu ftir a oiitr t1%o 14ithotwl aii injectioin hieing disc4ernhible
at thet 8501 :ih lei eI or alitte. In prattivalli% all oif thfet rawse. an exlaminatioen tof win&l at 21WHI4 or 349)0 feet
tiwl'Iost', a dis-tinct ctilt air injec'tioin (tiitig the i'.ethvrrniv at 11511 nih) taking place at leicPls 114.14)1 the. 850 nib......... ........tingl. . it is nevess.% to ime alert to tlilm0. ui-iiliI. if tihe ojitinulin forecast eflicienti . requiredl.
Ihc-t' st t inn in' r amni nt Ito it re than mintr in rpt res-iom bu~liit Itespite. or slit-ra pi b-ct iset of. their14.11k Itrt'~~ilrt gradliets'. theN' freqiaentli catim- the mnost 14 idv'-;rt'at anti jitiert'st fliing 14eather oif an-,via-'. of stqorm'.. Iw hr.% comtitutte le.- thani I lm-rcent (if all vc icgenetic ta-c'..
1.8 t. Ngwtirt. Patterns
Ani injtttion is nti foilloiwedt hi* ci titgent'si %4hen the flou1 pat ttrn i, loart if a general nmrthim4est flowl
toi the east tif the injetctioin. Figure 20 illtistrates -tch a caw'.
1.9. EXAMIPLES
Somet ill ust rat it ns t f thlie It'eh n ilt. ftor foettastin', M~tIt t1 id ni he relateti prtoble'ms art- preted t44
in Figs. 21 Ithiuid .1l. 14hichi arte actual vase, fromn (t dta~t -ami i -v kph'lm lix I). The fipure lvgentl-
juont out in t'aci c'ase pe-rtinent feattures cif the pirtiblem.
ALN %YS VORIK t Iu NT I ( S1 1:1)11 %IN C %N BEl (:IIIKEk )It SHEETII IS COtMPL'EED
I)D.. all i njecti. i t STO
(b.) At levelm beo 8501 l.? (Si., paige 49.), 0 (:,,lid ton~gue at anl, I'-. ci? (!v ai. ~g-. 39.If a i.-i. .r to u41 3 is i144. Own ii lc %tcw .ioliton bren dii forrva- , i. cli .grnre im . anl k jid. If yr., tohI')or I (0 f.wre.ast in accord m.l i-tr tll-11. if I ia) 1 .rotor..
F.irst d1ate aoid t 11114 injctli .i1p.;ae r. I If inlject 4ion hal cooint 1 fr( orm
jirevi.' g ina.p-. mill it oini.1ik act 1,. erpe a pr''ioo.iil forrcaoot va-v. of ci cI..gcriii. (o.r p~age 24 ).If a n. .r ve-. check Ktlvooi he
IfC (1Is .lrthI * f 37 IA t itodl. k-ci page" 34 ),hro- ato loco . imn iir if appjro priate . ....
3. Spercial camett.(a) I),Wr. a lledti% e litteni raai-t at 8510 nil See- Fig. 201. ...
If s. ,. fi.trvi-t fll i1 . cleii awnl chec~k lo) hre.... . -
(h.) k. till# parrot v% ibiiie lwt-i.'al ( :atrgozi.r r lo;agr,, 38 ail 114.........If-ti. fiirecd-.. d- ill-trmlct,., an't check -tiop here..
(c) I I.-.- a -iii jcci% r re, ir% o.f th 5011V lnil- iiirt oai4 cM Ir dilini tel, unfavo .rale coindlitionsf.' c t c'gelwooiln.- ! Oigi- 34 andl 99 anid Fig. 03. ) If so, ii n..uirr all suilisrijuent findaingos inti - light.
4. ( omr-.. of parenlt Cc ,in... (derg).
If 18.1..or fou r. ii i.r-r i- I.trE -n 61 and 1411 arIN o l .1. - ill.- ilico. in circl (rof Iigz. 6, pred irt cen terjjllinifri mln 18.1lilt'ir-1.111 alildin-ck -t.ip hirr (fi rrca-t in-tIrilitimim page 29) ... .. .. .. ......
5. If either v- -iia-lit oil it linie t ii not nirt. iriiieriI I. detrmrnine:(a) I isancr li-i'. irn CI anil ceniterr 4 pf;arent I14.% miles.I10 ( :ntral -ra It-%. el pr-m of piarrot lo rat ibih.
( inrlillt Fig. 8. If pN. ii t fall- Wiowii l.. ilt# i% . fi irvi-ir- I i-ciilg of( parenit, no c,*clogrnesim and check otop . ..
6. If pointi in 1-ig. 8 falk aliiiie cur%' r firrcia-t ii il..gcnr.sk at cast.
7. IAwatiiin.(a) Coinmtrilct kiilnn..lial area it wo.rkin~g chart friim Fig. 10.Ii0 A flat i. mationiam raneie of ti-m,.ratutn in i-ithirrm rililan in 351 milro? C).
Fiirrca-t -anii' Latitude. a- C.1 if 1 -I5S for higher ko lues inn'. m~ onth in thr kidney area. and for
(c') A~ hatI i - meain Ii.irot atoii 4f -trface friont? (deg).The' niic it.. ith-mioutI t he frionlt . te. fartllrr nothl cicliigenrsis i ooli Ibe fi iecamt (sre Fig. I I analp~agr 32 ).
(d1) If no piarrnt low'.. frrvat ii i~iigrnri% in Siitihawrot lairtiiin iif idnei.(r) I fciirflit in theme. inidication, f..rraat -ame latituade ato C 1.
P'redIictedI hatiiin ..f ct, cli grnrsis
8. Intro-it'.
(a) 810(lo tnmlierattarr range (of injec-tio.n(I.0 854-nih. avetage w mu in ijectioin .. (lat).
Initial inti'n-it'. of nrw *tirm from Fig. 13(r.) 1oll.mli trouighu -harlinera- (coirrrcted, for latitude lay table on piagrlO) (ft).
(dl) 1olt~i-ml teliipiiratolre gradlient 111114) m i. east of troulghi (C).Storm iotiltfit prtedictioln Figs. I 1. I5. 16
(a) I )riin tat ii n of cmiiitolro, 850 mh .. . ...... (dleg).(Ii 0 4 rien tat io n of iot hrrtin 854) trit.. ...... (deg).(c)l imnplit nil. of isi tlirins.............I(di ) Iirc~ it injl. I-it fromi Fig. 16 ...Froim ai erage oftl(a), (is) correctedl from Fig. 17, initial course is fourecamt as.......m (deg).
10. Spieed.(a) No-eirr.-entati'.e graisttilphic wind 850) inl kt(b.) ATIIHNM) inilr, nortllwest from l-claigenesis (854) ml.) (I)From Fig. I8A ajedi is fornecast foir first 12 boaitl as .(miph).
11. Verifica tion.C:enter julmp. Cvcloainei. No cyclogenesis ocriorrd. (Circle one).Timr foirmed....... . east. IAWAtiin...........Initial: Track ... . Slited . .... ... ... Intensity..........Maximum intensity in 30 Loom' after tlaatim ..................Raeas
Fig. p Actual example. 850mb chart for 2200E. 23 November -Q47. A center jump case. A primary cyclone, centralpressure of 100S mb, is only M5 miles from center of injection. Note -be easterly course of the primary cyclone which is arequirument for the center jump. Timing is almout the same on center jump cases as for new cyclogencais and the action usuallytakes plave well north of the latitude of the injection.
... . .. "- :I..
'L 98
.. .- . ,. .- . ~' .
- r __ -'.- .... - -, ,-",* LO W .. . . .<,. ,,,.,
'/I .5. 1 .-- "P / . . .
, '- "- L
4. / 5H -U-
IL--K-- '.
Fig. 29. Actual example. 50-mb chart for 100OF., 7 ecember 1947. A negative a. The injectio while of excellent defini-tion is only S60 miles from the center of the surface low center which has a central presoure of 992 mb. No cyclogenesis woaldbe predicted except for deepening of the primary low and that is what occurred. Such cases usually leave a temporary weakbar metric depression with no had weather associated to the southwest of the center of injection but in this paper these havenot been termed cyclones.
IL
1 'h 06"5
to.~
L LOW o0t- 5. - .*4
-a - . -.. 10.-\tr -
A. 9 P I1* 25 PH 4, ;~ 0.*
7'' .. . .. .-
oe. .7 . . . . . .
lig . t. ~.niimpe of( i. pro-ir~tioi fact,,r. v,m.rid % ilhthri. faim-t*.j .. ,rt.* .' 4 1). mn.-r 11017 %hili %. tp
t clii. ,il-ril Zt. jiilar. (f .1,.% t4- fall oni \.-,. I *.rk :itt, litltif a %pac' 4f a ft-% lur-. *1 hiis a juirtitm 4 Ot Ai.. Wiimli map,
ca'!. it.. Pr-. itj.t m o r -4 - -'it V tol i *.rL -istldl It.... bet f..r,c.t t n tlit. litte. l-,-r the vmidl.ht ,nt p~r- d _-di t I - -
*t.Iroa ... It vaii-rd, lthe -i.....iII. *e 1i g 31.
* N,
'N - \ ~ ~.-20*I-2
~~10
0 , 0
105
CG
*.V *' 1.*10
-X'NEW STORM DEVELOPS, *- HERE 0730, 26DEC 1947 .P42
SP- HOUR
fig. 31. 't ..ecti,,n ,f time'7(M.ml, duart foir 1tNl'. 25 I)e'emlwr 1947. TIhe 'nld toingue'tip.' .. injectit~n ia charlI ii.iille'. N4.iitilmj.i %a% llijsernihile at 850 ml. limit a Rimilar a'iId Itinpime won apmpare'nt at SIX) ml,. lilank analyses'. ..h.,i ;.i saall -tivrmd*-l.ed. ill Fig. 301 mottling 1nirtim"Ie.. and ramu.ing the' ..niow at Ne'w Yoork. bumt a eareftl i'heek e-ledrl% 4iti4 that ii,tiilfi,r.l t he loath imdicated. %u hlori.' rnntire'lv ne'% ..tirm fmmre'd ipff mh~r a.. intdicatird lt ratnac the Nre ,irk mnt,%. 1'ro-ifilitm
.torlt11s lie it ti le req uireed jle e-itie n, bt i ciii c''~a'e e ('144 lerede in tli- "(1e't igatiecr one or the other
hias twturred. I loel~t~e'r t Iiew~ 'cws are- rare'. 1, igre 11) is anl 4eample of ibt % le,. ie. of h. Iteejet je tiiatiofl.
There ue4rv it noiler ocf ot-'as.ieon during tis toed' Ow.ten innr tlv 1 res-iecn- foeruede, 1 artie'ularly aloeng
tile e'ast coias.t cef the Unitedl States'. anld im'r~isted4 feir it cia' ocr t'%4e i hoout ame' inljctioen l-iii dlis'ernile
at the' 851) nuibe i'.el ocr adie'. lit Inprac4tie'ai% till cef th4- ca-'. all e~aninateen ef i jls at 214)4 oer MWN~ fe'et
tdii-'lcm-d a elisiic't cold14 air inj4e'tlcrl (usinug the isoetheerms- at W-01 ini taking lilclee at l(I,e'l 6-14 the 850) uit
.ej+ Ac'erdlinglh . it 't'4vesar toem alert to this- pcc-.ilpilit% if the opjtiIIoeml forecast e'flieeiec, is r'c jire'd.
Thes-e sto4rms l@~ ne'r a n li nt I( to wore tblan ii inir dl4j re--ic ills Imht ele iit e. 4or pcerheapsc Im-aed o'f. tbeir
iteak peressure gradlienIts. the,. freqceuetI cadee'4 thi' le-ot idesr'a ande INoer.t fu ing '.eeathier ef an'.
Ani injectio i4s1 no lt foleehi'd b,% ci e'iege'ne'is ihen' the' fiuei pat tern i's part of a g'eeral rwirtiit 4t flo%
toe the cast oef the injee'tiedn. Figure 201 illoetratet och a vse
Soee illus-traetions. of thle teceheniqe' foer fcereea,.teueti c\ vblccet~e-i- ade the related perobllems are jere'-enteel
in Figs. 21 throogh 31. %.nhc are actual ca-c- freeilc t d'al~ta -ameie , hce' \eIejm'teei'\ IL 'l. T'e figure l4genel-
pioint out in eat-i c'ase jeert mne'nt fe'atires oef tihe pcrolem.
A ,.atnp~lc %iee siv.et for jcrat-ticaI appjlic'atioen oef this fcere'a~ting it-'ehi-iici can Ice fouened oIl jceeg 50.
I Doa-~ all inij.rti.ioa rpit? STOP)J(if ) At 8.,f fill.!
(W. At Ieva-lp loo-I'a 850 miii? (Sr liag'. 49.)a-) Go~ld tontguer at all .%~ .-i? haa page- 39.
If at-.a-er to till 3 ill not. t~w l ca - w aa tip a*.aimi lia-r- amfa fort-4-a..t noti- i~l-firo..g-a-..of auv kinld. If vr". topI ki.) .*r 1(0- fi.ra-aat fi avecord %..ih ili-tri't.'i- aiao if I () jorot--ard.
2. ir-t plate- and timae iopija-.-in Jm-.arrii . If injorrtitin baa. hadl continuity from
iprecediiihg ticp-. % ill it aiiact .1-..iaa. a ,.e .'akfa,rra-aat oaaa- of c~aI~eiai.(-rr page 24 )
If an-t-er , e-, ciecl -top~ ,liif liarre
if C , i-twi-h!64f37 latitude -rva-cJaI 34 ilrl-tiaclmi er-iparapia.
3. Spercial a o(a) I) caaa-ai' a ~nr -tat)O5 nil? SreFig. 20.. ...
0 D-- a a -ta lojec-ti~oa rreirl ,.f thr 54141-ni. alahart indalicate airiititrl% tin la irali conalj iionmf..r ci a-I.geni ,? 1'aigr. 34 anti 99 and Fag. 63.) If too.,C cii-aidrr all -a irluent t aicalingo, in
If 18.1. .ar fiat ire a- 'ir-c a - l-h ii cn 6a anati 01aid 18-li, ar aoii i. ii e% in i-ira-It of lig. Em. parediact cenriii nip fr .aaa 18.1.. ar a. -it i. anla. id-t' helire ( fa armca-at iuan-tci mo.p;age 29 ).... .. .. ..
5. If ratlir a-aandlt 'iit in e I i, foot flit. iriaa-aoif t- aleternint:
(a) I i-ata nce l-a-tiot l cr1 I antl cente i .f fiar-ua to% a mileas.lb) C entral -ara 1,-% el part irr iaf paarraot hI. ma. Ki!
al *,.1i1i ig. M. I f 1. 'jult fall-. lana ha t he ar t -. f. r .am-t alerjaenintg aif piarenmit. not cml ahgtnt-i amid click v.taa
6. I f 1. Pint iii t ig. 8 falla ala. i r c-lan r f. .r.- 1 o-. i l..gamr~i at Capt.
,. I aa-ati..,n.a) G-. na-t rait k a uv--a;-iarea .~if a ark jg ilhart friom Fig. I 0.
(1 a t fat I. nia i mi iii ri ii,- af 't -mp.-rat lire al ii- thirrn rillilf in 3501 m iii-a? -
F. areva - -anolilaI.t it ida- a- IJ if 'I = 1IS fiat higher .altra mm a- a. alit ain time k ialne an-a. ati fa ar
I. .aer. n..rtlhw.aral.
(a-) X% fiat i- wana winaatati--a of -aarfaa-e fraaat? .(leg).
lii ila.,rc ii' r li.i -a mth tilti- fri alt. thle farther noirthI cyelago-iita -ahmtlal Ibe fa araat (-an- Jig. I I analpaage 32 ).
(d1) If tii. jlariit hai 'r,% a. aiaiglar-i ill -. ,ittimat 1aarti,,n maflkidnory.(ar) If ii itiflait inl tiii-. analia-al iata- f areaat %aine la ti tud noil , aC 1.
8.-aio irittai-o-fiti
(a )811.mI, ta-mfaeratiro- range aif injec-tiaan ()(b) 8
51-ni. atocrag.- t il in imjat iain (k t P).
lii a in ta-n-it~ %af na-%.a -atirm froim Fig. 13(a-) 1 ll)-ni ii tr' 'agh Ii aaran-si (aa rtecteil flt atitud aitfa tabale oan laagt 20) (ft )
(ii) SI l-vl.ta i. arn;aaratalr grailialit IONI m ii. ra-at iaf triatagli*ta arm initraa-i t preict i ion Fig... It. 15. I 6
1). Inait ial Iiar-ae.
(a) f iianit atill oaf ci-at t aln 8504) na. .. . . . . .. )10 ) f ria-aitat uan aif i-aat i--m.. 8150 m I........(l-)
(a.) %inpl it iale aif ia-a tlietmt.............([at )
(a4) Fa ra-a-a -t ia ta-ma-it $r froim Fig. If (a . .irlria at, a-tag- oif a9(a), (1p) ciarrecteal froim Fig. 17. initial coriatr i.. faartat a--. (ali-g).
I 0. Spei-id(a) lit-;ana-entaja-a ga-aitroiphir windl 850 mrial (k t").)hb) AI tMIl miii-- nianthawriot froim cyiogene-im (85AI mup)( )Froam Fig. 18, ipa-eal i-a foireasat fiat firoot 12 humrs ao (milli).%I 'tarificatiaiai.Center jump. Cyclogrilieiot Nip evw-Iieit, ac-rreil (CircIe oane).Time- fiarmd r aapt. lbovatioan.. .........Initial: Track - l,4 . . .r .i IntensityMIaximu~m intenmity in 30 hoarp, after foirmation... ... .............IMamarks:
51
i. E(:vIi(;I I D(1l CNiD)%S
1. 1. IV )(I'I ciCiT itN
B% i'ictln ,t'~l~Ii ie are' tlloe that art' lewitaee bvlofithi a1 lpl'eedi lIlt 4)f fccrtllme~t fleiw at
I I sl I Il I ' s .I 1% e l~le'lIIIi- -IIIt%i4-1 ii1~ a i.eft tat Ilea-4 I'ec't 1in heel eeJ.,If tile-Iil m e4rilee-icaI 'I- cheei re.
se'arch. lhlrtlcr. ,fitlellll thiot ilrrtflle'4eelteIe','e%, ill N.ertll Iilt-6rIt~ i- limfitede toe iii,- lereeat area cornl.jiri-ilg thel i Ie if thli ei llil-kt% Mmm iti-. tit,- prrt'et'iit afeervva~et 1,d- too at large r'gimi 4e tile' mertie'rn plain
stat'- adi cenitral 11 .aimdta. lit blee itje- 4f all ( .aege~ I v.\elefle- ceim-idlrv'e Ii tis repocrt ialt e''flhoitwfl
ill 1i. 2. A iiether (or wit ( att'geer I leess acre' miviiqm'ctec toe ''lee ifti Il m llltaicl'' areas totitidi' ifC Nowcth
Ameitrica i- flet kn4ceu it. ( ategeer. Ic. t'ltes' art, 41111 tli-ial: t.it' liteimr eef ail a% e. g t' It' 14 ti timesi 1wr iinth
inl thle 1%iter -i'd-icr.
'Illi" iti-atiooten pore'ent- ict'rtille'nt falt i vinem'rlilg ie' -lriji 4i Nerti \lcle'rivaii ( :aego. I e'. oimes,
andl li-ill--' ill etail -Ic~iic ftlre'ia-tiiel pnellltll'n if 4111T' 11'eeelt'11, 111 '' taliti liet'nt -t'a-lt''. l c'. cinie'
anti IT-)' W Ii cigittidtIt). 'I 'll* noteirn leit' spheclcre sea -it e'lica r ts eccetl ll t li t ticet iii e eeiamu se tf I lite' 2 t-Ic ur
interv.al be't wee ic cei'si ' e mcapis. 'T'e nile ts elf e erigi natie cc icC 1 .a t e'ge i I 1e s'' * 'mic' deta ils Ceci'erting
ecare jeresecnted Icelow.
1.31. 'I'l! Cvchoc An lIf~ i n as~ a St'paruIlf (:tllfr,,, the far .Nfrfttt'it
Allo :10it ( Iwcetut of tiht ( :ategqcr, I v'ii-1ines %ere tra'ed bcek teo thceeac.lae ni. eater
is.lantds area, anti re'asmitaicle e.itlen'e w as fecicie 4)f tl.'artit tico'.t'le'tt fron this area itc the ('atqgert Ilece-atieci tcf thet Ihow. TIhe dtlictiecn loe'tooef a i-i ' lttt inc tis~ greeig amied a i'iilqee in the fiticc'.,ing grecsill
('Allii It feercis itt a icort ie'ast .ism Ilwiest treceagi) is notil '.a'.ssc e-ient . If thet v'.eleie was filiteid Ii a
sie'a -Ic'e'l Iii ghl-ire''..ire ritdge. tile 14)w was ca talqe gil as file ts iii. 'l:' 1. i cea I 74)l'c Ipja ttern "liecis a
I 100 0 100 200 300 400 500
STArUTE MILES 648 6
90 217 18 9
31 65 95 16 2015I3 9 7 9
43 51 96 72-62 3339498 41 62 14
0.40 252303 27 - 27' 94
80 45
38548 63885
7 5 93 546I0 0 977
56 62
32 / ,
19•
0160
Jie . 32. (Original hwa-ion dif ('ateguiry I (clo~nes. 'l'h.' p~mitiuna ii all ( .atrg.ir | r'vd'lne. (eae I thri tigh ItX)) are H|O l
SIN.1e'. 'Ihe. E'riiM hiih'hing id~rleate lie m.aulin I aare'a aitil it- hI. . lad h iu.'h w re i i .1 n.' mnovqmettu N. n umrral. iitdih~th.('alew5 I86m3l8et,
ul cl'-t toed t , \..llItiIllerilie. Ahve ijili'. i. - ti ieeclte'eI 11ti 1 1. t-) I Il i ''elii' Tlii- rid-e
ifa It41re. n,.t'liIa I It , .'~(l-1 if, Ie lI% I, I Ile'- lce'Ar\eee4 . 4'11 -ric et Ic~ - t 'll) -I% I. L I if 12th 2 ( h..t'e I hell.%cho'.
1 .32. Ii'1 b i ~ c I .,, lit iit A on thil #,%I -SomIll, vit '11"11.01)I I hit ( I It#-ntA It mi if o Iij Iaj L s i i ths (;it f
I flted ll llt- ve If lit- Rm-kMminains As his rmid m~i ie lml e'at. tIh eloi
inll ilt' trmli - 4 tbi ttf (oil' \ Iaitlt. iThe tttlt't''air c'titoetui peatte'rn is simtilar tee tile fir'.t nile. eefoigin.
% itith it~e tlori--tlli ri-1L--v ef hligih jre'tsure at tilt, A4'et coeast 4c Nerth \mettrit', anitit I ~in41 Ba.% 14m.
nellt11 forttt't eili 6 iul.- lte It i~tvpor% 1. It is. itelresting tee mle' ill jta-ittg that. %Iivrvae'J lllee-t ( .tt'l,r% II-% ce.lt -t en%% I ItI t ie 7001.1m1 ItoIeelr flattIt'rn. t ie,.t' fe14 c'ases w lic I'i elbe ele' iat. I v mrkI'til freii the 'te'ri lg
culrre'nt hadtc thetir cirigiit il ltiee~ httrtil-'eltili trllit.
Nearni'1 I m'rceml itf lit- ( :it tege eM I t''c t'e,~ clrigitlate w4ithitc appliiarentt assis~tance' fronm a parent low,4
and eetlt~iel (of it 1ei-i'tl'eelor ierire trtttgi. Itt c'lliria-t te the otiter mttes' 4ef eigil. these. t'ellsgele'ra~lk feerlt *tttith 4e 1,-) \ Lttituiean ~lti ar tilt' imlteltaitt. Thetre' ajlj'ars toe lot' to rt'a-te. itlelc'ler.
14If% ti i elc'llrre'lte ejtyltl~ take place ill .111 lre'a. ItI i. elilietfill if foerec'asting paramtle'rs k aliti for other
t" lt's eef co,~ t'leegc'lte'i' call iot' apitlie i t til t1le'% Its 1%. 'I lt- are' 4feef, iierl c'oe. lte till' nimteltllitt. atnd
ltre'mt't nitiC-mill Ilepie' at tert-. Tihe llieil'l..ll it te'rit I- again s.imilatr to) tilt' othter gt'tmtlis. lThe
seta'le'rl et-~iire iatterivs are' ge'ttetaI ll.t rk an ill t.
Tl.lek I Ied te~tnl II pie'-tilt O th eeton ell t-c vrigiii 4ef ( .tte'-ert I coc t'let': htt4tiwe'r. It has be'etn
atetttttl that litfe-a e'lveltlc'tvlt '1ll4 tttee'tltt i m th s tqprm!.l arn' ii'1i4'tlentt 4f titt mtotic 0ferigiit.
Tlhe gn 414 ill cir c 'ca% idee coi e n'.lltoe% i ll f tIl in lie nt hii 14et tineer ti iert114lst flow1 alotft pre'sentsi a perob.
Ie'it toe tilt' fell'clastl'l ill tilt' I iitee S'tlats. MIie t cliie' steerllt tni cimilo, af'ctling till' %cat th'r it tilt
'enttral ande v'a-elvrt I ttitel stlal'- 'iginat'il tin" ectilmanner. ( .ate'geer'I 1' iocl'"v are jet'tltl' telfill oir tee li~t
33..00017-16 17 -36 1610 17
ooooo5 00
3b
-24 -23 -10 C)- 10 -21
14 914 1 -3
10
1919
16 518
19 ommatttto, -18.0-00,+ 3 12?_ t 322
23 22 9
- 14 17 1 9 08
1 4 4 118 1100 6 1000 -5
-12+
314 9 1 D __14
22 4 z_tl 16
30
STATION MODEL 3500 MB TEMP700 MB TEMPTEMP DIFF OR b
33. 111,1A.1111 % 111drx J-plcth f,,r a iomitilhag I at,-w-r I clclmw. N-,tv, thr ieu tahht arra -tithimr-t aml tho, Atablean-a wrt1ea-t,,f Ow -tchow mod thr iii-tabdii.% imb-z gradwittwrietitud The axis thrmigh thrI..% r,-wrr i, Itcri-Fidicular to the 71mp.mb comt.mr-.
uillimit appro-cialple do-o-loviiitig. Thi- k iti comira l Ito Calepw% 1\ lom. %hich freiltictith deept-ii. Cmise.
ilm-sill flic f4pro-ca-I pi-4,1plem i it, do-lermim- Ili@- rair 4 fillitig. i.c.. the nmidwer of limir, until coompletv ilkap.
lwarative frimi Ilw svallier map. Cticlmie . %hich lwr kl fir limp-r flum III himr are called "monfilliiig."
search for Ilifom- invamiralple fcaltire, ipf Ihe -timplic %hivh inighl qli liwsiish the fillim, frmu
lilt- 114011fillilig v vlollvs i. iflllplilivql "llen lilt- imilcr vtm ideralion are all iii it imiiar arra of the
2 '+4
-3YS
100 070 0 0 0 0
16TUEMIE
Fi.3. .taniti me ~I' w a T ' t.n npr i, l *.,.. ~t~ri I'~~i001 ~dtrb
o we.3. 1wIgnli~~~ I .rF~ 3
~i~15 \5t'n~lf. it~ .tt ~- i ti~I aeir .'-~ u hr wi~tiiirhietI~I
109r jI 12I aeriri, i li'cseiia ii ie I ;-I.,ie i -38ee' he'f'. hd le'elIr~i
ghereee aj ici ~~e~I~m~~ii.f~eer- e~--u~Ii i~i, he eter l, Ii~reie fthe ~12i,* i,
it III01 ).1111i 1e' It~. I li- i-.qthet aloi iio-trat % ariatimi, ill Ialom- rate, 4i% er iat' region. itir tii lattr
red-oi, tilt -ttltu are- calit linit' ip iri-talilit'. anid ile indi'.itlual tt'rnia'ratore dijffe-rcllues arr callt-d
I.TUO tiirll04)tt- nIlaps 1)f lte.i' i%4tI1 t6 (of in-tatilit,. ut're lra'.in fair eatil ttf -tieral Ia.%te-. one fora'. rd .alo' ' tli-( vetr I Itiw- ant tilt' oitir ftiraverage '.aiae-.of a gromsaji ti ittillling lot'.4. liie-eti tillptt itvt'nap dhil se.tral inilmtrtanit ft-atre1 (1umie of A hit-i art- appjarent inl Fig . 33 and 31t).
1. The Iine if d n iiiilit ' for the 7411). to .51W.mb la'.er il-tratedi titnct tiifft'rnt1im-t'.4enr filling andti nifilling vci ne4. Th'ie 850. ttl 7W-)mii anti 81), to l44-o a'. cr4
cliii ma tt 'rijia~.izc the- contrast sea well.
.2. I ntaitilitv grat-ri'ts are weak ant ilul-dlefined for filling lows. Fear nonifilling lpi'. . a
4tihnute u-ojiictii pattern was appiarent.
.1 i' ll a ~imiti Illrailo-nnt 4 if in ~ta lpii tv was dtiret-ced n tlia-.tiithwet t unii til te
jiii-itii of tit(- ca-le~ '.t' I a '.t'it tile it'nifilling t'tmujaitisti mapi. lIn tiit casetC ofilling
c.%cltrlt'. Almos~t mo gradiuent was4 hiiw n aig this line.
f. llt '(701. fi to) ). t'tillja~itc c'harts intlicatei that ile pe-rtinent ft-at-s~ of lte-
iln-taipilit. jiat torns i ,'re wit hiin a raditis of I t))4 mniles frotile healw venter.
It %ia - tit' i ie rliinet thia tt ilit-e tiuffitrtli'es bet wte 0 i i figm andl lt in iiing 4.'. ei te. mt app are lt till tlit
maiiliij-tatli ee'.gai cotfrt i-Iair0; i cit i 4lc~
2. 0 MB C'n wr r Nc t 2 -i iO m r al l u i c-1 r ltc11imiIa xi i.
1w it 37. r'tl i I 'll pe oiiit Iiil~rt mr in til mo co-hta e r. a lin- t iti gl t h j i o-- the r atI at it -
ang ael tel tind .t~- i titititir fi tli . Themir - ;I,- -1.11() ,imtae r mile-.ai boothi a lic al rnd --mjtiiiai
If o;t-iil uf tile niilt- foro em . % - cIN)m l tcline I 1111 ilot- th"l if I Iii~itll iil~ cii tilling iiituu
filin (imoo ;at'tiiiiti i viii ake-omc a itrcmt. Neillo i lig, alil- iiiiiii ighniatgraie al ndil tiletttil'
ixrtontt ie din inll illtliex r a i nt i r atit-l iiiv jeiilen t ailt-~ ivlthv I eets. ~ iitl'toi i2itugt l c. T epertu ittre ah i . ta H i it cr alow tilt-a nileri Aer g ir ii'14ti 41 earm it Od at ith 700 o iihi- li 11
3aht . Th iri diii~ iffei~l renc i n't Iv ini tir hi- tA l t 7w- 111 aii in ( llmni b iel. 'i iat -r lac e' cm cle dint int rctiota..t.h inta;triit tt in'co % the n dertelr itnetd.nteee lejn-i trc,. o det
The neic et e iii inpe e fiitlii~ n v ole l u ie h m gitl-loo e tra da ih
An v fre'qute-nh 'e ntrtir facor. in tret 3.5tge'n'cis in w aen ti tichor- it terlm al to) m-464,1 n dia
59
the relationship between developnent of Category I cyclones and wavelength. It was found that a definite
correlation was present: the greater the wavelength of the 704t-mh, contour pattern, tile more likely theoccurrence of a nonfilling Category I cvclone. The wavelength poarameter used was the measurement at
7N) mbla of the half wavelength in degrees latitude measured along the latitude of the low cell from the western
ridge line to the eastern trough line. This is illustrated in Fig. 36.
'he natural partner of wavelength is amplitude. This, too, was investigated and it was found thatfor a given wavelength. there was a preferred amplitude favoring nonfilling of Category I cyclones. Theamplitude factor is the measurement at 7(X) nib of the amplitude in degrees latitude. This is made byfollowing the contour over the low upstream to the most northern latitude and downstream to the mostsouthern latitude.' The difference is the amplitude. This is illustrated in Fig. 36.
At this stage of the research on development of Category I cyclones, there are three parameters: insta-bilitv contrast, wavelength, and amplitude. When the preliminary correlation of instability contrast andwavelength was tested with an additional data group, however, it was apparent that the investigation hadnot included a fourth factor traditionally of importance in development, namelh a consideration of advection.It was necessary to analyze and introduce quantitatively the temperature advection field either as a primaryfactor or as a corrective term. The most satisfactory yardstick for this advective component was deter.mined as follows: measure the geostrophic wind velocity at 850 mb over the low center,' and move "upcontour" this velocity times 24 hours. The difference between the temperature at this point and over the
low is the advective term. It is negative if colder air is encountered in proceeding upsteam. This isillustrated in Fig. 37.
The four parameters may all be measured objectivel.. Table 2 of Appendix I presents the pertinentvalues. By means of multiple correlation techniques, they were correlated for each cyclone in the data
sample to achieve a forecast of the number of hours until filling.
Stage I of the multiple correlation, relating the instability contrast with the advective term, is presentedin Fig. 38. Each cyclone in the basic data group was entered on this chart. The family of curves was
fitted by inspection and arbitrarily numbered front 0 to 7. The stage I curves give good separation betweenfilling and nonfilling cases. The construction was designed, however, to give optimum separation on the
final composite graph only.
Stage 2 of the multiple correlaton is presented in Fig. 39, and correlates the half wavelength with the
amplitude. Again, the family of curves was to give optimum results only when combined with stage 1.
Using stage I value as the abscissa and stage 2 as the ordinate, the final and composite graph is attainedand is shown in Fig. 40. Primarily, the final graph provides separation between filling and nonfilling cyclonesof Category 1; in addition, it measures the rate of filling. The stage values and the forecast results aretabulated in Table 2 of Appendix II.
The following conclusions may be drawn by referring to Fig. 38:
1. With a constant advective term, the larger the instability contrast the greater thetendency for the low to persist up to a certain high value near 1.-16. Beyond this point,the trend may be toward filling. Insufficient data in this graph area prevent definite
conclusions.
I If the contour over the low center is closed, estimate the amplitude parameter from the nearest open contour.3 If very nearly in the center of a closed cell. assume a speed of 5 knots in the ulirecin of the prevailing upstream flow.
STAGE I
2 \,,
U' +4 ---030 - - 23N N N
>J 100, 8t 2/ N N
N -1- 3b N-
.. ../ _ __,_.__
7 6 .00 4-. /./ - \- 30/i
-,) - . ./ .. I
/
L . 42 8 N 1N 18 I0>. N
~~..,." "24 4 N.JN '
2- 4 6 a4 2 14 1 18 20
I4N STAB Tm T /ES A E P
STAG E 2
N 2 N
30 - / 30.
>7 3 6 N 36
02 4
< 2A5 32
NN
33
30 i 30
2 N N
J I 12 I 2,4 I NN 4 42 30 N15 N N t
n N / i0 %N
65 2
C MNNN
015 2 2 0 5 404->s
70 MBHL '2INT EGSLA
61
COMPOSITE GRAPH (NOT FINAL, SEE FIG. 41)> 5N N N
48
5 _ _ __ _ _ N _14_
30%30 36 N N
,8 30 N N NN4 N-IS-
W 18j . 30 N N24I N N
(36 1 24 \ NN
3 8-3042- 36 ~6
03 48___
0 1 2 3 4 5 6 7 > 7STAGE I
-36- h tar. adlj ar'.aa rqlir.. at filii aga' iI.a
STr % ; V L. Fig, 38. Iaa-tnaitoo'il tnra-11 D raw anl aui- ta ttiw 511anal7Nd aahr- .raida.la to Illt, 71I f-til aim~r.
*t'.t-r ft,' .tjrf~av,-k itt , tr. Dltrinint It-onfwralara ilrff-ro'rro 700 nil. miii,- .INI nial. at tiltt-aail ajtrr'. i.I, i joot
fiflol faaile, vaita-r -.1.. .f I1- . '.tilttraa- aiiiatafl aitafa'' N I- o Ill. (rooma' fri,,, na~'aai (afjac--it owr ?olo t,f Iot.. criil-r
ti- i.lfferencea I- iii.- 4-mtitr.ooot.
Wotilor aqt *in. i.a Ifir. i ga'aa-trnipi.- looliid lo'. io a if,.a-at' t'r -airfavr how. a-cater at 8- till.. ~l' -aaaa ti llttt
ga'rin. Nagoata li aln- a-It,) ac ,4 ad'. a'tiai. Siaca Fig. 37.
ST '; 1- 2. Fia. :11). 7IN)-t i.a ,1'. .aooala'agtia. %taaaaarat ii. 46agre-alatls--A mu . Il,,aa ii. arallaI .,%,,r Ilt,- I.,%. ,ater frtalitfll
ritiga' lint' %,It 'f If. i .111 A . till' irtigi line-. r'a-1. '.a lag. lta.
CO P%! T i' GRAiil( II i. Fig. ill. If;. jilt fall. Ia.llah right atfff Ill -i. ar laa.-. the ~ al 'a will lwrr-oit (Air tat fa'q I-t l i,tar..
air olloiil af'jrlar. If paainrt fallo. '..itlainiala- fanail aa ajr'. a.'o. tliii' maadair s4ffatir- maold fillinag is Iificat.l.
TIlS GH 41If AS 45 lEN kFISED4:, SEF FIG. 41
,t a aly Fig?.. 38. 31). anail t I to, Ci atag.ary I I va~roo. I Iie iia..I it Il . tI I onIra-I .a'.. li aoirim ii paarpaa-mi.aalar ttt powj' it to A t'f af , ,-ta;
fill cange in oathlaar lomrtanitar..
>5 R N3-----4 N N NN N N~ N
{ NN
N N~30N N N~
"30 240 36 NNNII N NN
18 130 N
>NPN
NV N6 30 N >24
3342 N
22 Ns 24.,_N_3
-30 N N
0 __6_18
0 1 2 3 4 67>7STAGE I
F~ig. 411. Saint av% fort hg*. 38, 39. and 44).
2. Withi a eain..ant in-tal'ilih a'uunrat. a lar.'e fleatiie aierti~pe teriti (coldl aili eatiott)
pro mo t es no n lillinw &u th Ile .ai~vci ii Irutn dcrca-es. I liec cia iuie lia, le-s t citlenu 14) t
jiersist, until. ujaaart reaching a jia aiti~a' adliect i~v term (A~arm aaliection). fillimg i., markedl.
It mtay be statedl fronm Fig. 39, that:
1. R~egardless of the aihllitooale. the longer tihe half wavelengthi. tihe greater tile tendenc%
to persist or dirlpjen.
2. If the half waiclengthI is coiilereal constant, there is a pireferred amplitudie for ;wer-sisteitee which is in tile range (if I,)' top 2.5 latitude.
The f allow ing co nclu sion armi 4 Ite tateal fraomi thle coioah i i a graphai of Vig. ti):
1. Stage I anal stage 2 jawaraauatvrs cuantrilite alaaaiit eaiauallN t4 th lii sparatian of the
Thes lle fintal vonilt iaiiim i stilirilir toi cit her stage I or stage 2 conialereal sejaratelN.
2. ( at ego r- I c~ alon ns epja rat ai into ili ing am atain i linig tN pes amid thle graphii prinailes a
mteastire of t lie rate oif fillinig. Ni o aimi'lisime. can lie idraw i a, it)i the rate aof atavwnin forcaIses king, i il Owa nassat1illingm ai flii a'uulaasitechart, thlinigli ahaaiit talf of these
ti'njt~~i'rmtiirtt- jiattrI I I niir e ttliitralit .rt.'i a 11 . aIIu1 . , I a aIa iit'dlt'I. t' I f i t. lijer1ltlir
Irdin fritin 7t it 4 1ti 1 I . iit'. 11 l of t-ur 1n 11 art a .11 _- I IIlo tif I r.tt I I ltreIaItI i f I nt I% It Ia'gu I Iit
To ii rtla t t ctaI i I IIIo of I ' tI it l ec t Ii tat 1 ' ' flitI I i i nn'- if It .1 1 . 1 1t' -. 1 rolilh att n m i, - i ill l I c % 4ii ' t me
lit'l ra 11tui. lift-in ohtriba'. t oltft-~ a itj a -i fro nt -ate t'r Ic' l i . 2ie tt'-t'n i f viiroes vii. I
lviated that -ima r n toi tift 4tl e 1i 3 Ikn 1 iiii ' i ~ aia if 4 iitit# 1 s arinr nuttio vac iir- ',it. h in i,
th- tjir triiti . f t u ll. The ;14tii 4pb 116. 11,1 datang did1 mo lt i- t a na' n c - t'i gtl t ,r if Ih -t'' tlt4 )( I it-c i% tjiiI, q lw't iftI i , a I II-ii p -I I v cl it Itili tf I 7 ait-itt. Iit - 4Ii ia it - I-it 4 if h 1i-4 I I I I iit I .' p o-intl
t lt, a r t , Ih voII(t a of )I t ,ra IIh (I . 3I i iaet' I i i ira i t. t e'IA a i I h'I. d nr I if . ' li or I ia I ,# if tlt n t erer It gitI
ph r i '.eI t(--I)% 1 ct'm n te- i a % I. t a ell Illtit rti''.d) i ii t l ata na d suaccuit tii' ~c~n i fai '~*c.c
fro tl wa ,it., I litif ix hit i tooi n A t I ith eI -jther I t t ~lIi.x t't, ore I icarI j'' ii ixt e t. licit I hlt' r i- ,j r.oar tife, it vr
hit f wa'. ptg l f lecliier a t cixjlr. t'om ni c a li if ilticarl it i . iii'. ltit 't ) if 116 : utagiar rnawa'ekneauM tloiii. m P)r I a ndtcc ,I itvr i a high i-t aih v Ia n ia4i rgi' ttl c'ji iii'a -trictlc.iI one ir Ia rvt'rkncs.
191 t).mti i titi n tma'.i'li'n 11h-%% al ic rti tlc'4ltt% Itti p a itiaft fo r kn , o 1t 1c' riax n diaext.-q i
If It.i% 1,- t tand d it11 .-1 t'.4'lait i ce h at a m xaifcti' it illtriitoliii'a tc off'litit ent Tif ( t'gi v~ilitne -I' d
beeni tiar'it 1 4t i i f orecasIg rai %-- Ilit- are ptr. I lcnttcI i i'ig, 38.io 31)_ anre. lIfIiivr' fin't it ig % I t % iit Itit
tflluc IAxi %, gra 1ih 1x oi ic.itt .1 1o 1 4atIxtia %% ttc'a t trt of v x Ig iictttt n t' i t ttit- jan m ated.d he-re o
A. r c - viaral titnrI iti Ic i%t' % fint'c'xtn ttIhlult fv thit do'' 11iac-ili -. 'Iatgr~ Ic~iltt' xu '
gadneien th fol.11tiwin111 fai. Also, an stnp ' araw iah ct it ihat rapi'dl iii.', 4f o i iagr ll alil I i'.,itinxit't'
anrd alie.gc' i, % practieald ap iiait tuftilt- initta bi them- Iftarecito n alc'r. ~r im laof it
a c A
-l r- -
6 Ti
- ~ 1L.t~ .
B1 - 6
-- ~ ~ 6 .B 5 4 U
U~An
- r-
%1111(k SiiHE [oil FH lIAST~ING( I)EV LOPMI;NT OF CATEGORIY I CYCLONES
iII4 11(l. %IlI NlT4: Sea %ee ~lieif~ii tatutre lorated under nortlaweal fllow .1m700mbs with past track from northiwest.
D ate: line Aiarfacr chart .Tigne upIpe Sir.....
MO0 700
1 r . o. -thle H0.710 4H.ili chartA the location of the sea level low (ignoringthe 3 .iir titne lag l.etwren istrfac and upiwr air charts) ... .. ....
2. At K5() III., gr. stro1.hit itin qtrlvped .,%,-r the I. iw is ........ ..................... x 24
'Iive opt c int ti r s)% er the Is) (-en lter this iit ante.
TInI x-jratiire at this, til~str..ani point I- . . . . . . . . . . . ......
'l'emjwratare ojs er low is .. . . . .. . .
D ifference (adv ret iv e tern ) i% . . . ..... ...
.At sI) miss ilraw line thirmi'h low% center p 1wioicoilar to bait of northwest nlowsoil indlicate 24MI-mile inti-ritalk for 14(00 miles rather side of low. Draw tWiidentical axisi on the 51k).mhi chart with the identical 200.mile interval markers.Vo.ter lorlow the tempieratures at each interval at bsoth levells:
Subltract the minimuom index wIch mulst lie to the northeast of the low frointhe miaximum indles which %ill lie adjacent tii the low or to the actuthwest. "hisdifference i4 the instaiiti, coiiltrant and is ...
A. ith adlvective term and instability contrast, enter Fig. X8
Stage I value is .. .... . .. . . ....
3. At 7(101 ml.. measure the .hi.tance in degrees latitude alng an east-weet linethrou~gh the low center froim the trough to the east to the ridge line west. Thisik the half w ai elength . . . .I. . . . . . .
At~ 7114) ni determinle the mi-t northern latitude and the moat sointhern latitudeif thi. ci intitur tlrmigh the low center, the difference is the amplitude ......
A. ith half wsavelength andt amplitude values, enter graph. Fig. 39.Stage 2 value i I .. . . . ... . . . . . . . .
4. 4 ith Atae I value from 2 abiove, and stage 2 value from 3 above. enter Fig. 41. lir
De(v elopment forecast is Filling within . .... .....................
Nonfilling .................. .......... ..
VERHIFICATION
FORECAST OBSERVED
Sliced .. . ........
Itirection
I nten-it , Fill or Nonhill
HVR7 GGW ~WSN
G 768 1767
77 815I01
764
BTM
679
7L
0i.4.~ onanIfune ra ae
PIH 50L0
57867
67
1.5. NqIINT'
Catcgor I vcdones gencrall% nimoe southcast ard with ,lo'eril of 20 to 10 knots. If these cyclones
ioer..t long enuiunh, hIonie r. the% %Ill recuri toiard th.' aortlhe.ast and thla, I"m a a ddhitional problem
in th' ino eineInt forecast. eliatim ,,f thi. recuri. attlre 'hara,.tcri-ti'. (Catcgor. I 4-Pclones move less
taniforikh than other 0' k-e. mith d vheleratioti often .o,-'arring prior to returvature. Acordingly, simple
extralodation tchnique-- %ork utoorli. Therefore, the ttoenjent forecast requires three elements: speed,
direction, and time of recutr atulre. The ieeld and direc tiin fore'a-te are fir a joerio( of 2t hours, or until
time of recurvature if tlii- i, earlier. 'lh forccast of tle time if recurvature is the nunldo-r of hotlr, btfore
the ci clone turns north of ,.a.t. If reeurt ature do's not occur within 30 hours thei c 'lone is called "non.
recurring" for that forecast o.eriol.
There are tso general lintitation-s to the mnovement forecasts of (Categorv I c. clones. These are geo.graphical and de%' , lmr,'nal. lo%. located in or inneediateli, east of the mountain ranges are erratic in
Ilocll eient t) a ioint of randninv. Acci',rdinglI.N it is necessar-, as the first step in the movement forecast
to exclude all ci clones wfhich are within IMt) miles of the Wyoming.Colorado.New Mexico mountains. This
area has been delineated in big. 2. The location of each Categori I low in the mountain area has already
l.en showin in Fig. 32. The large majority of these cyclones lie outside of the mountain area.
The second general limitation imposed on the movement forecast depends on the development of the celi.
Those ci clones which fill rapidly require a different movement forecast from those which persist or deepen.
Obviously, a frontal wave filling rapidly is a shallow systein, whereas one which is intensifying is likely to
affect a deeper laver of the troposphere.
1.31. .. _-__.
The forecast of the speed of movement for Category I cyclones is dependent on the persistence of the low.
If the cy.'one fills in 18 hours or less, speed prediction is neither possible nor desirable.
The cyclones, as they fill, move irregularly. The majority move faster than the 7fK)-mb
geostrophic wind over them.
If the cvcilonefills in 21 to 42 hours, its speed will be approximately that of the 700.mb
geostrophic wind over the low for a period of 24 hours, or until the time of recurvaiure
if this is earlier. This relationship is illustrated in Fig. 43.
If the cvclone persists longer than 42 hours, the speed of movement of the cyclone is related
to the thermal patterns aloft. In general, the greater the thermal gradient in the quadrant
northeast of the low center, and the farther the low center lies west of the isotherm trough,
the greater will be its speed. The parameters wshich describe these thermal characteristics
are illustrated in Fig. 44. The first is the measurement at 700 mb of the temperature
difference between the low center and the coldest air in the northeast quadrant within 1000
miles. The second, also at 700 mb, is the distance in degrees latitude eastward from the
low to the center of the cold isotherm trough. These two parameters are correlated in
Fig. 45.
The summarized data for the speed of movement of all Category I cases are given in Table 3 of Appendix II.
50-
d45
0z
~40
0
w
035
0
0
0
Is2 5303 040 CULSEDO O NKOT O 4HUSO NI
TIEO EUVTUEI ALE
Fig. 43.___ F_______ graph__ (,r__r___(_aegr c fi- ih ili_ 4
Firem dJp~ .%% 3. th riagim e.I g..l .f I~ thicg 0r 1 ) rv mmeti li t h tin 2f th 42 lecnire
t r i c~ i ii'i i over thl cii piro% cided at'i i Ii cor1 fi reci ,. '.i i iia co rreld mio n cfi ciew si f 0.b00. 1V henl iii i e!d- le i.t i iitI the ccciiri c grim (vow, 0,-,. c~ t I re cwili 100). liqi mv i r. Ice ci crcla ie c efficien t droedjjc
61)
CA-2. NO0 M270
1~fk DEC100- 9
-20Fm.44 ;edfres ps~ri.t~.fr ililn U~gir c.Lnei Te"asmmTeprauet~ferne 0 hemwaiaeI l~ei.fr 11I wIi .*a11 i 'n A .bct e iiies on i . i.i eatiiiorn iti 11 ie
ifth w nir i i i tl,.21 k 1Ia ac as i h (u.-15ga'i heaatace niereso ait..fo
the ~~~ ~ ~ ~ O 0icne ' .n t.i u i ntreiiuottri.ihr nmhes fseI',wahtelttd ieo h o
1.32. Iirs~iin offMtoomen
are. illuSraed iFigs. 46 pandore 47:r contouiseing isrgr nI r'*ormTe omon tha T eaue Diferece is th.
30--20K 30 4050o I II 37
I 33
S25 - -- 4- -- 38 -
4 430 43
co 35 5
3549
35 49
~ 523 30 -40 -33 --- 403 - 40 -
z0 ~2032 20
-J23 2929o 34
0- -- ------ --- 331 36 - -36U 19
0 17
22
WL -~ --- 25__
z r\ r +0.84
00 5 1 5z 53
MAYIMUMV TEMPERATURE DIFFERENCE FROM THE LOW TO 1000 MILESFROM THE LOW IN THE NORTHEAST QUADRANT AT 700 MB (DEG CENT)
Fig. Io. tvor-a .r gra ph bor *r .wel tof ,ownfilling .m ig. .r I c t chne.. Th~e ctirve.. re1,re'.ent ii .recaut .;werds anti thIe ii lmlurAMr..uiua icc.~.luth in kimao for 2t la,,nrK,r intil Ow onu - rectirv attire. Srchlg.tt .
The development tof the low clisals.o impoortant in forecasting tite iretiomn of moot ion.
If theI' velnflsin 18 hours (or less. it in l min erail '% the mnajorit, i dci iate to the
right of thle steering current, often as murlh its 20'. The probahrilitti of mrarked right
dheviation is greatly increased if the ci clone htas origiriated 1)% forming in the sounthern end(of a north-mmuth trongh (see Section 1.3t).
If the m-clonepf'rsists lon ger than 18 hours. the foertrsioaa , e asonable steering,
as defined above. for 2t hours, or wntil t he time aif recui at uure, if this is earlier.
Fig. 47. A" m ri mn d in f, antqw ~ir a l m in- trig vefined f r- di ntrn cu r' . i th 1,.% '1~ h~n,.enua dire,-
Inc1m i1wtrak t ie I wf Iwi h c"n t.. (Ir innan l withn ir ti ac ofur. dt tti,, rm o.tu
514 r7 V- 0% %%I e%00 N
2.1 NV 220E-100
700 MB CONTOURS 30--AND ISOTHERM S -
Fig. WR. ltecr~ lr e tr forreva-t parainmter.. f.r I ategomr I rs e n'. I,.. The 1.,,l' rmm-rattarr 111%, r dwi I ,%* i
Mtovi itg do% it -trrjini mi ,p, ime cont our or'r I t,- Io% tit,- pint1.- .4l.o it l ~the ldm~hrm hio. ifi co-kie~ air troi thle loi, 1,1t
do%~ nltreatn troumgl. i - 2.1C 'I'i..nitar tir iTretw Do i itreanl l. 21 No. t. i. .- d .Itowd, *th1rio'-ove~r the Io%~ aimo tit, hint of it 1wrtmrl..tm..n jmt -tnrtmg to form, T ac l m a mtI trark of Im li, 1,.%Imm i mr~-ian ~~i.of i18howia n..un aturr.
Unie-s filling or rt'mtrvattare inte~need. ,Ieiatmi fromt'crirtg %~ it mttwttr.d for flit- 2 I-lioulr Imwihitli.
Ji 1 40r ii %toot i.i.1,. i iir stie i.n~i .1 ie- fi .ilecrt. b rc- ;~ulatic~ceri130r .. ir cice. I c 110i -i.c i.rii,4 .,gr I 0lgp- ,ii~ieii 1;rc.iiac crlritin
LOWer .\ \cctr
b I.u-
T~iie eC~;peei~II;eei il-tie ~ie-a' la~ (irdret n i rne~ titt i (.ie~i~ i ccne.0hectnri rii~edta ilnin~J~iiii~il.aleai in-ecirct.I- i~ej50ul-
I.~3. ihw nj .00rtu
'lni i iciti~la~ in tmeinInetr-iifcr tnecilmehent-te lne 0tierl cf ~nt cr i eo
ciliie-iiti t *vorwti er .411111111 1 tite tu eiecr h c lii 0ei- li jt c ietieCes. I
ig i'eto). i 6ti cini lrimir' nIece..r n- ieti a tie'I'l "'al 12 :.tt'gc r fi,'l 1- 19. nainaiii ~,- c tee ie thi rtifIcmnticcn icC It'i tr e igin ic g Iirt-iri tietii't e ue.a',il ieii 1 ~ ~ tuci Aj.cac' t i -a ire're anhii~
ije i , . ite iii ile flit-litle if titi. N-c r e i- et cclio~ hiici e iii o no aleing t f eait li-. r.ti' titant (of
4'-tlcvic li tckt roi w.or ithr of 3311u'. fi-lit- ca'.c' 12-qot fit-IInic later. atte vlit-t.III- twr' t ii ah it
Fig 54. n.:1reurvng(atgov Icilon. n (ntaattoFi. U. oteth coplte baneeofan ia~hem ze Nowvethe ow. theactul tackof te lw. how l~varrw..illu~trte.e~unnel aterig. wthot rcuratur, fr a leaut 0 hur0
Th reuvauae~orcat armte. re 'Fejwatre4 vr h.IM . I ( ad ieiwaur Iifernc ldamtpa.
3C te oue.tar onte aln 20 otu .- I ) iue Iad52ilsrt h unrhuino hs w
parm 40r toao06u0au efreat
deelpmn o aprtrbtonwhc 120 all ollw t40" treu' fatema-rs atir. Wtishort~ ~ tieatrtogIomtote(~ln uvs ot fes.Fgr 0ilsrtste70mpattern~~~~~~~~~~11 fo a aeoyIlwntascae4wt5 hra rs.Ti ateni o odcv otog
formationtk and is* thrfr#soitdwt 4r1uvn os ti vdn fot h aata h re
of ev n s ~e. cr s,,et fbti n rec rva u 0 '0i l a s f lo e o e e , a m ir c l r l t o s ibeteentw thrma-cestchaaceritic ad stbsqunt ecuvaurewasfond o hveforcasin
mesreis feciens n r~tin ectvaue a the00 acua te4rtr oe h owaWPh dfeec
b et w ee n~00 this te p r t r n4hWod s ir f u d d i n t e n l n.il o t u v r t e l w h
measurement of thes %acor is"ho n 1nig. 8an 0. hs w aa eesar onie nasnl
grph(Fg.SI uwu1wic has beenE st1 wrmssd atilfcres aeedsae3
75
With an isotherm crest of given effectiveness - i.e., a specific stage 3 value - the time lag beforerecurvature depends also on the character of the wave pattern in hich the crest is embedded. This featurecan be measured by utilizing the stage 2 value from the development forecast (see pp. 59 and 62 and Fig. 39).in which half wavelength and amplitude measurements are combined. The composite graph correlating
stage 2 with stage 3 is presented in Fig. 52; this diagram specifies the number of hours until recurvature
(up to 30 hours). Table 3 of Appendix I1 presents the data relative to this recurvature problem for all
Category I cyclones.
The control group of data was again analyzed for recurvature features in order to test the validity ofthis forecasting device. The results were satisfactory, although no measurement of statistical significancewas derived. Appendix Ill presents the pertinent control group data. A diagram summarizing the com-plete movement forecasting for Category I cycloses is shown on page 78. A sample work sheet for practi-
cal application of the method by the forecaster is also given.
FOR FIGS. 51 AND 52"
OPEN CIRCLES 0 ARE RECURVING CYCLONES; NUMERALS ARE TIMES OF RECURVATURE.
FILLED CIRCLES 0 ARE CYCLONES WHICH 0D NOT RErURVE IN 30 HOURS OR LESS.
SEE TEXT. p. a9 FOR DEFINITION OF STEERING.
CASES WHICH FILLED PRIOR TO FORECAST RECURVE TIME, OR WITHIN 6 HOURS THEREOF, ARE
NOT PLOTTED ON FIG. 32. THESE CASES ARE LISTED BELOW:
CASE NO. TIME OF FILLING FORECAST RECURVE TIME STAGE S/ STAGE 2
8 18 HR 24 HR 4.7/4.2
14 24 (20) 4.2/M
20 so 24 5.4/2.1
21 12 24 5.3/2.1
23 Is 1 7.0/ 3.0
29 Is s0 4.2/0.0
30 24 s0 4.6/3.3
34 Is 30 4.5/ 1.1
41 so 24 5.5/2.1
67 Is 24 5.8/2.7
71 6 so 3.7/4.2
76
00
-25
z
00-J 0I
0
>
a, -5 4 0
00
0.0L0
100
0 0 10IS2253
TEMPERATURE DIFFERE-NCE ("C) BETWEEN LOW AND COLDESTAIR DOWNSTREAM FROM LOW (ALONG CONTOUR OVER LOW)
Fig. St. Forecast graph for recarvature of Category I cyclones. Use of this graph is the first step in a recurvature forecast.The family of curvea provide stage 3 values, which are utilized in Fig. 52. the final forecat graph.
77
7_
6
30 0
~ 4 24 3O
03
0
0 z300
z
0 2 3 4 3 >STAGE 2
(FROM DEVELOPMENT FORECAST SECTION - FIG.39)
Fig. .52. The final forecast graph for the recurvature of Category I cyclones. To forecast the time of recurvature. enter thestage 3 'values from Fig. 51 and the stage 2 values fromt Fig. 39 (of the development section). The resultant forecast is thenumber of hours until recurvature. (Ilecurvature occurs when the cyclone turns north of cast.)
tl~ll2r iHCAST FORl CATEGORY I CY(LOANVS
NoRTIIWI.'T FIPtY. AT 700 MR ... WITH IIA.Wr TR ACK FROM T11 F NORTH WUST.
Refer toYig.Q4. It low is in mountain area no directiom-speed forecast canbe made. See p. 67.
[f low. isnot in mountain &r"s. refer to development forcaat. and time of filing SeFigs. 38.,39 and 40. and p. 59.
It low fi61an 18 hours o less. no speed fore. If flling in 24-42 hours. measure gin. If persisting longer than 42 he&.cast can be ssade. atrophic wind speed at 700 mh over I. At 700 sub, meassure in dog. Bat. the
low. Refer to Fig. 43. See p. 67. diatance east to the cold tongue. See p.67ad Fig. 44.
2. At 700 mh. determine mazinum tern.peratue differeiner between low and coldeet
On en average, speed will be faster than 700. ir in northeast quadrant within 1000 mile.mb Sow and direction willbe 20' to right of See p. 67 andl Fitt. 44. Refer to Fig. 4S.
ToO foroam time ofrcu5tun determine the fore
1.At 700 th.eampercotor otea erloneener
clone ~2 Att t00 loca the dovrnca epeaue ewe the low.Snp 0I cread checonilydto cylnewtkecn
found downstream aloe8 the ontour over the low. Seep. 73 and Fig. 481.
79
WORK SHEET FOR FORECASTING MOVEMENT OF CATEGORY I CYCLONES
Date...................................... Time Surface Chanrt.....................................lime Upper Air ......
700
1. Refer to Fig. 42. If sea-lovel cyclone is located in mountain arei, no direction-speedforeaat can be made by this method. If low is not in miountains. determine fromFigs. 38.39. and 41 development forecast.
2. If low is forecast to fill within 18 bra or les,. no movement forecast can be made. Onan average, speed will be greater than 700.mb flow, and direction to right of steeringcurrent at 700 mb.
S. If cyclone will fill within 24-42 bre, speed will be approximately that of the 7004mbgeostrophic wind speed over the low. See Fig. 43 for speed forecast. ..........
If cyclone will persist longer than 42 bra, at 700 mb. measure distance in dogeea latitudeeast to the cold tongue (thermal trough)................................ .................... La ItitudeAt 700 mb. determine temperature over low and coldest temperature within 1000 milesin northeast quadrant from low.
Temperature over low..................................... ....................Coldest temperature to northeast............................ ....... ............Maximum temperature difference is ........................................
With distance east to cold tongue and maximum temperature diffeence. enter Fig. 4S.Forecast speed of low is......................................................... .................
4. For all cyclones persisting 24 bra or longer, to forecast direction, examine 700-mbcontours over low. If it curves anticyclonically downstream, or straight, move withlocal flow immnediately over low ...................................... ....................If contours curve cyclonically (even slightly),steer within the contour channel over low ..........
S. For all cyclone persisting 24 bra or longer, to forecast time of recurvature, detearuineon 700 mb the temperature over the low ..............................At 700mbs, locate the coldest air found by moving downstream along the contour overthe low (not crossing the trough). Coldest downstream temperature is .............. ............700-mb temperature minus coldest downstream temperature is .............................With 700.mb temperature over low and temperature difference downstream, enterFig. 51. Stage3 value is ................................................ ....................Refer to development forecast. and note value used there for stage 2. See Fig-3 .. 39.........
'With stage 3 value and stage 2 value, enter Fig. S2 time of recurvatureis .....................
6. Move the Category I cyclone with the speed frum 3 above, in the direction indicatedfrom 4 above, for the number of hours until recurvature from 5 above, or if non-rcurv.ins for 24 bre ......................................................... ....................
Forecast position of low ..................................................At tim e.. . . . . . . . . . . . . . . . . . . . . . . . . . . . ...........
80)
2. CATEGORY !1 CYCLONES
2.1. ! NRODI'c/'ION
Category 1 1 c-clones are defined as c% clones with a past track from the northwest quadrant and located
under s.uthwe.t flo% at 74) mh[. but the flow is produced by a minor perturbation in a basically northwest
i1o%, pattern. Ait examle of this type (of low can he sei.t in Fig. 49.
The distinction ietween a mere perttirliation and major trough at 7W0 mb is easily made subjectively.
llowcecr, an objective inethod for determining %hethler a ci clone fits Category 11 is as follows:
I. -%t 700 rob, locate the surface position of the low and the associated trough that is producing the
southwest flow.
2. From the latitudeof the low, measure in degreeslatitude the amplitudesof the contour through the low
at the major ridge to the west (a,.) and the minor ridge to the east (t.). Als) measure the latitude difference
of this contour from the minor ridge to the major trough further east (af). These amplitude measurements
arc illustrated in Fig. I(b).
When a. is less than both a. and a/, then the case is assigned to Category It- however, if a. is greater
than 10 degrees latitude, then the trough is msJor regardless of other considerations, and the ease is assigned
to C:ategory Ill. These lows are not essentially different from Category I cyclones, and forecasting tech-
niqjues are nearly identical. Separate treatment is accorded them for reasons of clarity and continuity.
lit sharp contrast to Category I lows, these cyclones are prone to he nonfilling; cases where filling occurred in
less than 21 hours are rare. Categor% I c clones are found in the same general area as Category I cyclones.
Cateeorv 1! ciclones were less frequent than Category I. occurring less than once per month in the winter
season.
2.2. DATA
Appendix IV presents the data for the Category ii cyclones that were studied, employing the same data
sample used for Category I cyclones.
2.3. ORIGIN
The pattern of origination is not definitive because of the small sample of Category II lows, however,
some statements are pertinent. Numerous Category 11 cyclones originated as Category I lows under
northwest flow. Some of these are included in the Category I data sample; others, for analytical reasons,
could not be handled until they fell into Category 11, though the origin was obvious. Some cyclones origi-
nated as Category II; the first appearance of the surface low was beneath a perturbation at 700 mb.
A Category 11 cyclone can sometimes develop from a Category III pattern. In this instance, the
amplitude measurements which defined the trough as a major system are altered by intensification of the
western ridge aloft. The resulting trough becomes a perturbation and the cyclone is classified as Category It.
2.4. DEVEIOPMENT OF CATEGORY 1I CYCLONES
It would be expected that Category 11 cyclones would develop similarly to those of Category I because
of the basic similarity of the upper-air patterns. This was found to be the case.
2.41. Iniabiljit Conasat Paramneter tSee Section 1.4. p. 56
In aplling tile conlcepit of instabilit'. contrast to thne Category 11 cyclone, only one change from theCategory I itechniquie wits neressar% anrd that was the- orie'ntation of thelinestalbmlit. index axis. lli inference,(:ategeory 11 axes should be aligned pe'rpendicuilar ito thme basic neirtlIivoest flow pat tern which has been dlk-
turbed. In piracti'e, this is diflicialt. CSjbefiatlk ill the eeas with a brtoadi shallow pecrturbation. AX tech.nique which accomplishes almost the samne endi is ito aligni the axis perpendlicular to) the past track of the low.
The instabilit% contrast parameter is not 0'. cr1'. sensitive to small changes in axis alignment. nor to minor
temperature variations. This axis oirienita tion produced acceptable results.
2.32. 850-mbh Teme'rature .4dirctive Term (See Section 1.4. p. 59)
This factor in development is used in the same manner as for Category I cyclones. G;enerally, thc850-mb patterns present a more accentuatede trough s *ystem with the low and a greater temperature gradientthan a Category I cyclone. (;onseejuentl% . tihe advective term is more important in Category 11 eases. Theawtrage advective term for Category I lows was - 10; it is slightly greater than -5' for Category 11 cyclones.
2.43. Half Wat-ength and .- mnplitude (See Section I.A. p. 56 )
Thle measurements for half wave-length andi ainplitude are made. in the saine mianner as for Categori. Icy clones. The measuremuents are for the basic macroo-irt'ulat ion pattern. voinjol-telY i-anoring the small areaof southwest flow (lae to the perturbation. It would ber expoeted that ( ategor% 1I ci clones wtoutld occur
with longer wavelengths, thtan Cate-gorv% I c~ cine-s, .iyivc' the ,.re-.ence of a pertuarbatiotn in the northwestflow to) a great extent predicates, a lonig~r wavelen-th. 'lhis Isas founid itop ieu: uas'rltg half Wavelengthfor Categor% I was 330 latitude: for Categoiry1 cI e'%clone's. L"2. Thje amplitudoe relationship between the
categories is4 not so obvious. with onl% a difference of.-)' between average ampljitudes.
In suinmari the technique for handling Categor. I I c% cliones is similar to that for handling Category 1.
The axis; at 700) nil) for dletermnination of the instahiilitv contrast paramneter is laid out differenth - other thanthat the parameters are measured and utilized in the same fashion. Individual stage 1.2-composite graphs
are not presented. The composite graph. Fig. i. does include each Category 11 case, plotted from theoriginal data listed in Appendix IV. The validity of the Category 11 technique could not be tested on inde-pendent data since the control grotip (see A ppendix IIH) included only two cy clones of this type. For prac-
tical application of the forecasting device on development of Category I I cyclones, the fort-caster is referredto pp. 78 - 79, which presents a schematic diagram of the method andl a sample work sheet.
The investigation of the movement of Category I cyclones emphasized that the forecast problem dealtwith the specific time-interval during which the cyclone was moving from the northwest; when recurvatureoccurred, no prediction of movement could be made.
The time of recurvature of Category 11 cyclones is 01-12 hours (see Appendix IV)-. almost 50 percent actu-ally recurve in "zero" hours, meaning that the track changes to north of east immediately. For this reasonnoforecast can be made of speed or direction. Further, the only feasible recurvature forecast iso that recurtutureuiil occur uithin thne next 12 hours, (this forecast is madte without reference to thermal patterns). Thereafter,the cyclone is handled like those of Category IV and the forecaster is referred to that section of this report.
82
CATEGORY III CYCLONES
R. D. ROCHE AND H1. B. VISSCHER
1.I. INTRODUCTION
The Category III cyclone is one that moves southeast beneath southwest flow at 700 nab due to a majortrough at that level. To determine objectively whether or not the trough should be considered as amajor entity, it is necessary to consider the amplitudes of the trough-ridge pattern at 700 mb. The objectivetechnique has been presented in Category II Cyclones on page 80. For Category III cyclones, measure theamplitudes a,, a,,, a. If a. is greater than 10 degrees latitude, the case is Category III; if a. is greater thaneither a, or a,, the cyclone is also Category III. This category of cyclones is important because the cycloneshave a history of movement across the wind flow aloft and a high percentage of prognostic errors areassociated with a continuation of this movement. A typical Category III cyclone is shown in Fig. 1(c).The initial location of all Category III cyclones has been shown in Fig. 53; it is possible that this type ofstorm may be indigenous to the region just east of the Rocky Mountains. These cyclones occur lessfrequently than Category I, only one to two times per month in a winter season.
The forecasting devices for development and movement of Category III cyclones are not comparable indetail nor in accuracy to devices for cyclones of other categories. Though the sea-level systems are generallylarge and relatively mature, they are often multicentered and lack compactness, and to a large degree thiscomplexity prohibits precise analysis.
1.2. DATA
The sample data was the same as for Categories I and 11; Category III cyclones are rae numbers201-239. The same independent data for control purposes were used here, involving cases 240-267. Tables1 and 2 in Appendix V cover these data.
1.3. ORIGIN
Although the time .elationship between the four categories of cyclones has been substantiated, few of theCategory III lows can be shown to have passed through the Category I or II periods. This is not surprising,however, since the transition from Category I or II to Category III or IV is usually rapid, and upper aircharts 12 hours apart may well miss a stage. The majority of Category III cyclones formed in the mountain-lee area under southwest flow aloft, or moved in fron the Canadian Mountain area aeros the upper air flow;however, the origin is not pertinent to the forecasting devices presented here.
1.4. DEVELOPMENT OF CATEGORY III CYCLONES
Approximately 50 percent of these cyclones do not materially change their intensities within a 30-hourperiod; 25 percent fill (decrease in intensity) and 25 percent deepen. The development forecast is thereforeof lesser importance than for other categories. Figure 54 diagrams the intensity changes for all Category IIIcases, and indicates the forecast ranges for filling, no-change, and deepening cases; intensity measurementshave been made according to the method described on p. 18. The development forecast then con.cerns predicting an increase in intensity-count of 5 or more (deepening), a change of less than 5 in either
3 06 2 .07Fig. 53. Lcatio, of all Category Ii cyclones. Numerals indicate case uumbers.
direction (no-change), a decrease of greater than 5 but still a closed circulation stem (filing), or a decreaseof intensity count of greater than 5 with a resulting pressure trough only (flingtotrouh).
A strong indicator of intensity change for Category 1II cyclones was immediately apparent in the centralpressure of the sea-level cy clone: in general, a pressure of 1000 mb or higher was associated with filling to atrough, filling, or no.change; when the central pressure was less than 1000 mb, no-change, or deepeningpredominated. The arbitrary dividing line of 1000 mb appears to be significant.With cyclones whose central pressure was higher than 1000 nib, it was found that the location of thetrough aloft was a controlling feature of the intensity change, especially in determining whether or not the
84
INITIAL INTENSITY COUNT
FILL 1 IT TO E- FILL- NO CHANGE -> D DEE EN
TROUGH I25
0
00a 0O @00
* 0 0 0 •0 150
0 0 0 •
0 000 01000 0
0°
0
TROUGH >-I0 -10 -5 ±" +5 +10 >+10I
INTENSITY CHANGE IN 30 HOURS
Fig. 54. Intensity change@ within 30-hour period for all Category III cyclones. This diagram illustrate* the ranges for thedevelopment forecast.
cyclone would fill to a trough. With cvclones whose central pressure was less than 1000 mb, the locationof the trough aloft was less pertinent. Two other factors indicated the growth or decay of the storm. Thesewere the height of the 500.mb contour over the low and the 700-mb half wavelength.
In attempts to express the central pressure parameter in a more direct component of development,
numerous upper air factors were tried. Thermal patterns and contour configurations produced two other
possible solutions. Tests on independent data were indeterminate however, and moreover, the results werenot superior to the simple technique shown above. Therefore, the following procedure is outlined for
forecasting the development of Category III cyclones for a 30-hour period:
1. At the time of classification of the cyclone as Category III, determine the lowest central
pressure of the sea level system.
2. If the central pressure is 1000 mb or higher,
a. Examine the 500-mb chart for the location of a closed system at that level (shownby actual closed contours, or definite easterly winds, or reversal of north-south height
profile in that area). If there is a closed cell within 800 miles of the surface low loca.tion, dwsqiug Kill! mr.
85
Fig. ~ ~ 1 550carnn fdsac pcuata 0 bfrfrcsigtedvlpeto aeoy11lw we eta
prssr 174 7or th n10 b. I hsils0ainteu0otu itne sgetrta 20mls
940 600i
RIDG,u
500
960 TROUGH LINE
SFC LOWPo3tTION980
1000
40"A
9 00
120, 110, too"
so* 0 loo 0 .600 Soo,T'jg WILIS
STATO,
300
CA3E NO. 2225 MAR 1930 - 2200E700 M8 CONTOUR PATTERN
Fig.% The meaosarement of half wavelength at 700 mb for forecasting the development of Category III Iowa (with a centralpeamin ImathanI000mb). The wavelength measurement bere is 12*.
87
(n >1200 ----.. - IF CLOSED LOW AT 500MB. I/ WITHIN 800 MI FORECAST"2 S DEEPENING: LOW
FILL TO TROUGH CASE NO. 35- 4) (400W)0 z 55- 40 (800NW)
-- J59- 0 (600WNW)1-I 1000 .. .. 66- 0 (500NW)
II-01 -1
0.0 0NO CHANGE
400 F I L L10Z 700 X
MI 1000 MB 1005MB 1010 MB
LOWEST CENTRAL PRESS L.SFC) IN LOW
Fig. 57. tDevelopment forP(ea,. graph for (;ategot, II | rrnes .ithc.-.ntra|pri*iurr IOO00mh ornmore.
b. If there is not a c ed low at 500 mb. measure in miles the distance up-contour
from the low to the edge of thle northwe , the location of the contour
trough). This measurement is illustrated in Fig. 55. Enter Fig. 57 lsith this dis-
tance parameter andI the surface central pressure. Forecast itntyhanges inaccordance with curves on thle graph.
3. If the central nressure of the surface cyclone is lower than 1000 mob, then at 700 mb,measure in degrees latittude the half wavelength of the contour pattern along thle latitude ofthe low cell from the trough line to the eastern ridge line. This is illustrated in Fig. 56.At 500 rob, determine the actusal contour height directly over tihe low center. Enter•Fig. 58 with these two measurements and forecast the intensity change accordingly.
The forecasting graphs in Figs. 57 and 58 contain the entire data sample, including tihe independentcontrol data. Tables 1 and 2 of Appendix V present thle specific measurements for all cases. The signifi-cance of the graphs is apparent without statistical evaluation. A sample work sheet designed for practicalapplication of this technique is presented at the end of this section.
1.5. MOVEMENT
The prognosis of movement of Category III storms is important. As pointed ouit earlier, errors in thisforecast are most common because the track of the cyclone is across the prevailing flow aloft. Unfortunately,the majority of these cyclones. while well-developed anid covering a large area, have a flat mti-centered corewhich makes it difficth to define any one point as thle '"center." For this reason. the movement forecastpresented here will deal with the primary-track of the cyclone and not with the detailed prognosis of directionand speed.
Fig. M8. th~eto;,ment forcoAit graph for Category III r..clonep w.ith central pressure less than I(00 int.
An idlentical iimenaent aniii Isbe performed by (eearge (Pi) to#) in connection witl] a group of
cyl nesling %oktae~stiarel across tlie- upper air flow%. Essenitialli% this anali sis established the fact
that the fiutumre path of the vc lciac is to a large degree depenvdent tipon thle thermal pat tern in the area at
700 nib. Thte present iniestigatiom has sheii that the deci emaent of the stormn is likewsise important.
If the ci clone is forecast to fall (based on Figs. 17i aid 518). it should be assiameel the track will be pre-
(lominatat Ii smuth. regardless of ticrutial patterns aloft. This alilear.s to be avtotrate ihlen falling to a trough
is forecast, isitla lesser significance when onl11 slighit filling is ~imo eel. heis eases are insolied here, less than
20 perent of the data samtple. Figuire 5() sliecs s an esample and the stibseepient patht of a Catego rv IIIci clone that filled to a troungh. It is ceemnii for the path tio be along the edge of die motuntains. It should
be borne in anind that this imeaaactt is not I% pical tef Jategori I II ci clones ic tit) d not fill.
Categori 1ll ci clones, fiorecast too dleepen ior to remain i nchanged are more celatnion than those forecast
to fill antd has a different pat tern of imoi elit . TIhese -sints mve sout heastisard across the flow
pattern to thie sotthern edge' of the isetliermn rileeen (referred to as, the thermnal crest area) on the 700.mb chart
at the timec of classification. thence rectarvitag and "steeriutg- %sith thec 7tN).mbin contour-flow at that point
in the pat tern. T'he ci clones fretinentl'. maintain faxed Iisitimis relatie eIo the cerntoiar-thernaal patterns
whicht are translating with the wind fleew at 700) tai: lacmeser. iii. instantaneous picture. i.e.. the locationof the thermal crest ton thte chtart for tlte time of classificaticen. gives higll reliable results in showing the
future track eof tlte lois. An e~anaple of a deepening Categori IlI ecione following this track is givenin Fig. 60.
89
alo 00hown.1
90
________60*
_0_0-
40'
AND ITHERMAL
Fig.~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~R 6. A a lofaCtgr IcyiefoeatodeenndtS Tk Nt th prnune isthr
rub . adthru aleret F om a sn psh t" vi wp in, hecylo e ov s out itoth ces aea an t e00eWvm.~~~~~~~~~~~~~ oin wihte70m otusovrtercrauepit
91
In forecasting movement of these cyclones by the above technique, it is necessary to delineate somewhat
subjectively the thermal crest and the isotherm ribbon. The general rule is that the southern edge of the
ribbon is at the isotherm south of which the spacing is about double that between the widest spaced isotherms
in the ribbon. Fignre 60) illustrates a well-defined riblon. It was found in this investigation that the
thermal crest center is a fairly accurate point of recurvature; however, a refinement is possible by considering
the original location of the cyclone. If located south of 35' latitude, the cyclone will recurve 200-400 milesnorth of the thermal crest area (and in these cases, the ribbon is usually poorly defined); if located north of450 latitude, the cyclone tends to recurve 200-400 miles south of the thermal crest area. Cyclones located
between 35-45* latitude recurve very close to the ideal crest-point.
Earlier, it was noted that Category III cyclones were often multicentered. An investigation of this
feature proved interesting although not especially helpful. Cyclones located north of approximately 45°
latitude divide into tlo cells when recurving, the primary cell behaving as described heretofore. The
secondary cell usually remains in the lee-of-the-mountain area, and must be treated as an independent
cyclone according to its category classification. lowever. when the Category III cyclone is located south
of about 350 latitude, it does not clearly divide as it recurves and for all practical purposes it remains as asingle cyclone. In the 35-450 zone, recurving cyclones may or may not leave behind them another low
pressure cell.
As mentioned before, the speed of movement of Category III cyclones was not amenable to treatment.
However, a general statement may be of value: Category III cyclones will move rapidly (at the extrapolated
speed or faster) until they reach the recurvature point; thereafter, rapid deceleration usually occurs as the
cyclones head northeast. A sample work sheet is presented on page 92 for forecasting the movement of
Category III cyclones.
92
WORK SHEET FOR FORECASTING CATEGORY III CYCLONES
REQUIREMENTS: Sea level cyclone of reasonable atature, located beneath aouthwest flow at 700 mb. with a past trackfrom the northwest.
Date ................................... Time SFC Ma&p. [Tine Uipper Air.
LOCATrION OF CATEGORY Ill CYCLONE. .. . . ... ..DEVELOPMENT:
1. From surface synoptic chart, the lowest central j,re.Nore of cyclone is .... mb,.2. If central pressure in 1000( mb or higher, mark position of surface lo% on the 5(X0-mb chart, ignoring 3-hr time lagbetween surface and uppe.r air maps.
(a) If there is a closed low at SOO0mb within 8100 miles of the location of the suirfa!'e cyclone. FORECAST DEEP.ENING; OF THE LOW. Yes or No.
(b) If no closed low at 500 mb. measure distance in miles. at 500 mb, tip-contour from the low to edge of north.west flow (usually contour trough).
This distance is mi.(From 1.) Central pressure of low is........mb.
Enter Fig. 57 with these two values andi FORECAST Fil~lIN(;. or NO CIAN(CE, sindicatedl.
Forecast:.
3. If central pre~sure is less than H000 mi). mark location of low at both 700. andl 500-mb chartq (ignoring 3.hr time lag).(a) At 7W0 mi). measure in degrees latitude the half wavelength,. mra~turing along latitude (of low from the trough
West to the ridge east.HIALF U.AVELENGTII IS . ..
(b) At 500 mb. determine height value of contour over low center in hundreds of feet.
500-mb HIEIGHT IS(c) Enter Fig. 58 with (a) and (b) values, and FORECAST NO CHANGE, or [DEEPENING. a- indicated.
Forecast:
VERIFICAT[ION: Initial intensity count
Intensity count 30 hrs laterChange in intensity: .Class
MOVEMENT: From Development forecast alwo~c, low isfilling or nanfiling.
1. If low isfiffing (either fill -to-trough. or filling), forecast movement of cyclone generally south. No speed forecast is,provided. Forecast.
2. If cyclone is nonfilling (either no-change, or deepening), locate cyclone on the 700.mI, ch~art. L.ATITUD)E OF LOS'is ........ .. .
D (a) Examine 700-mb chart for thermal-crest areas. Mark this 'recurvature area" on map.1 (I) If latitude of low is north of 44%, move cyclone along shortest path to point 200-400 miles south of recur-R vature area. Thereafter. recurve low wi'th 700-mb flow over this point.E LOCATION ........ . .............. .CT (2) If latitude of low is 35-4%0 move low along shortest path to recurvature area; thence recurve with 700-mb
I ~ ~~flow. ...... . .. ..
0 (3) If latitude of low is south of 35', move cyclone along shortest path to point 200-400 miles north of recur-N vature area (usually poorly defined in these cases). Thence, recurve low with 700-mb flow.
S (b) In general, these cyclones move faster than extrapolated speed to the recurvature area, or point.P FORECAST SPEED ...............E After recurvature, deceleration will occur ast low becomes "steered."E FORECAST SPEED ......................
D
3. Cyclones north of 44' usually leave a well -formed secondary cell west of them as they recurve. Forecast this secondarylow as an independent cyclone. Cyclones suth of 35* usually do not leave a secondary cell, but recurve as a singlewel. shaped cyclone.
VERIFICATION: RECIIRVATURE AREA: Fom i- CA.s,r ...... A C'IIA L
SP'EED) before recurvature FORIl E( ASTI . ACTU ALSP'EED) after recurvature FOR ECAST -ACTUAL.-
93
CATEGORY IV CYCLONES
H. J. SHAFER AND P. W. FI'NKE
1.1. INTRODUCTION
liv definition, Categor% IN c. clones are l,-aled under southwest flow and are moving from the south-
west. These cylones are .oinnion over the eastern half of the 'nited States anti are generally regarded as
deepening ti pe storms; they ot-cutr as frequently as ten times per month. For the purlIosem of this study,
the following definitions anI requisites apply:
a. The surface 'c lone is located under flow from the southwest quadrant at 850 mob, 700 nib, and[IN) ml,. Flow from north of west over the surface low precludes treatment under this section.
b. The history of movement of the ciclone must also be from the southwest quadrant for at least 12
hours prior to the time at whii'h the forecast is made.
c. No attempt should be made to apply the-e techniques to -secondary" type storms until such "see-ondaries" have become established entities (i.e.. a valid, separate and chosed surface circulation
has existed for at least 12 hours).
d. While not a requisite, it should be noted that no storms have been included in the independent or
dependent data %hose position at the time of forecast was west of the 95th meridian. It was
believed desirable to rule out as far as practical all possible orographic effects.
In contrast to Category I cyclones, which display a general tendency to fill, Category IV cyclones
generally tend to deepen.
1.2. APPLICATION
All forecasts are for a 30-hour period which begins with the time of the synoptic surface data. In the
section dealing with speed and direction of movement, the forecast values will be the 30-hour average speed
and direction. With some cyclones, frequent accelerations and course shifts make application of these values
for periods shorter than 18 to 24 hours questionable.
13. MEASUREMENTS
In studying cyclones of this category, considerable use has been made of the areas of cross-isotherm flowat 850 nib. These areas have also been called areas of "apparent warm or cold advection." It is recognizedthat these are not necessarily areas of real advection. The area of "apparent warm advection" at 850 mbis normally located in the northeast quadrant of the surface low in question, and the area of "apparentcold advection" in the southwest quadrant.
For simplicity of measurement, these large areas of cross-isotherm flow have been further defined tohave centers of action, designated A. and A,, for the warm and cold cro.s-isotherm flow respectively. Asshown in Fig. 61, these centers can be located objectively. The position of the surface cyclone is markedon the 850-mb chart. Contour line# south of this low position that are part of the 850-mb trough systemare noted. The forecaster may use his discretion in selecting one contour north of the low position if it isclearly part of a broad belt and channels the low with the next higher numbered contour. In the case of a
closed contour system at 850 mb, the innermost height line should not be used. If the system is flat, it is
94
LOW -50
- A.
-00(
Fig. 61. 1xication of 1., Mt0i nit). .m rio . .-r- -Iwrni fl-. on ii e m ,mdm-m..1 em nt mar ra nge- fr.-III at.. mt Ito 11I or
an average. temjwiratur of aimma t I In I-m -t. i.. p.,t 1. ! iii l .rt. pm mint It and Ia are (a mid the **ceta rr 4gf ra'.it.(or .4.) of the tria ngle i- the km lant-- at V N.-me. that thme vmi,,tmr .mi the, -umhr-.a- i at a v aidm mane. -mnce it doemc not ..xtendthrouigh the trough line.. The in-ole0-- .l.... ti,ta r i- mmml mr a .mlmld hrigtai.
advantageous to draw stjplilmeii~tar. ItitI-fiimmi cmmonor for greater detail. ( Note that if one suchl inet is
drawn, all must be drawn.)
Usually 3 or *t contours %,ill niemt the aliove reqjuirermnts. I )n eacht of these contoutrs. trae back to
the point where the wartre.-t air ik mini-nri col andi note- thtis to-in ra t tre. Then procemi downstream aloing
the contour until the indicateud Aariti am1'eemtimmn ce'iases andI recoinrd this tenllwratttre alson. Comipute tle'
average of these two temjmrattirm-s atintark tite Isiit errmsinnding to this average temperatutre oil thile
contour. After tite operation has bmeen marri-mi out for eat-i of tive valid conntouars.connect thle pioints b% lilies
to form a polygon and b% ijimial olmlmrmatimmn lo-ate tite "venter of gravit-, of tile IN)l-. got). Propier weight
should be given to a cluster mif pioints if onte eiiists. The center of gravit y of tile polygotn is definedi as .4
Frequently the average ternperat ures will fall on a straight line and .4. will be tile "balance" point of lte
line. A, is found in a sintilar ttannter excepit that the contour is followed upstream from the warnm terviier.ature until cold cross-isothermn flow ceases. All measurements in this section are made in statuate miles4 and
in centigrade degrees. Troughs are located as nearly as irnsoible by use of the wind data.
500 MB TEMPERATURE DIFFERENCE1000 MILES IN NORTHWEST QUADRANT
Fig. 62. Deepening or filling. A categorical forecast can be obtained for any cyclone whope initial intensity count is Iss don, IS.The ordinate, the 850-mb temperature factor, is illustrated in Fig. 77, and the abscissa in Fig. 64. When the SO0.mb trough lineis greater then 800 miles from the surface position of the low, measured along the latitude of the low, forecast a filling tendencyin the 30-hour period.
'H,
00 i000 m, ,1 000 M,
Fig. 63. Trough sharpness. 500 ob. Measure 1000 miles east and west of the 500-mb trough line at the latitude of the surfacelow. Find the maximum height difference BA and AC and add. Asuming 200-ft contours. in this eape the difrence BA isabout 700 ft and AC is about 500 ft for a total of 1200 ft. This value is them courrected for latitude by use of the table onpage 20 and becomes the trough sharpness.
1.4. DEVELOPMENT OF CATEGORY IV CYCLONES
Early in the study of these cyclones, it appeared that deepening and filling should be investigated in
relation to speed and steering. Although no direct results of this kind were obtained, a relationship was
discovered which enables an accurate development forecast to be made for certain of the low intensity
cyclones of this category.
Figure 62 illustrates this relationship. It can be used to give a quick answer to whether deepening.
no change, or filling will occur during the 30-hour period. One of the parameters used in the figure is called
the 650-mb Temperature Factor. It depends, to some degree, on the phase relationship between the wind
field and the temperature field and alo to some extent on the strength of the thermal structure at 850 mb.
This parameter is discaswd more fully in the section concerned with direction of movement (p. 116) and is
-250
A~ - 20*
~150
-5
SFC /0
/ LOW/
Fig. 6M. Strength of the temperature firtlt, 5004 nil. Findl the maximum trmlwrahure ,Iifterec between the position of thesurface low anti an arc Pool) mile., in the n..rtlusnm quadrant at 5004 ml,. In this case it is ashont 2 t'. This technique is also.used at 850) ml, and 7)1M) ml. for the determination of qwpeeif ofvemnent parametce.
sho)wn also in Fig. T77,. lThe s.econd parameter. alon.g thle ai- is i~t, iena~imotm teitwprature gradient
withbin I00 mN)nile4 inea ~ured at 100I itt in tfl,.it- nort t1 opi adra ut fromu flit- p. u-it iof of thet center of t he
surface low. rltliS meastirement is AIow it iii Fig. 0 L It has liveni foonti that ft- relatiomnship htweeti tihese
two p~aramelters is valid tutu for t*,.i..nes of inall initial initensit i (i.e.. viielot- Ahose initial ifltenfliti, cottt
is less titan l) For these low intensit% c ' clones. it apjwears frot Fig. 62 t hat a prime reipisite for deetien-ing is the puresence at .500n) of a broad. steep gradient of temilierat tre to ft, tnrthwesr-t of the surface low
with a marked tongume of cohld air to the west of the 810-Imlu trotagli line.
It wouald I1e exiiected that fte tirctalation arouind leejuening cyclones wottuld be such that warmn anti cold]
air would he brouight into flte circulation around tife low. iThis implies that ativection. prttjNortionfal in
intensity to wind sli'etd and temaijerature gradient, woldil ive inicated on tiit- chtarts. Emu'ellent results
were obotained uasing a variation (of this technique at 850) ml. on large intensit% c-.clones (intensity greater
"See page IM of tie Introdluction of this reptort for a discuission uf intensmity counts.
0 -
H500 M 1 500 M1
0 B A 0SFC-.. C
"" 156 200
Fig. 65. The 500-mb temperature factor. !siragure 500 miles rapt and wsess from the 54)0-mb trough line (A) at the latitudeof the surface low. Find the magnitude 0 f the tempierature difference Itissn pirnnt Bhandtittxiflt C. The 500.mb temperaturefactor is this difference prefixed by a piwitive -t-) sign if the a-older temperature is at Bt andi a negative (-) sign if C' is, colder.In thia case the temperature factor is about T 7.
titan 10). However, the advection parameter (to lie explainedl later). %slien t"edet ott ciclones of lesserintensitv, showed increasingly poorer results as the intial intean,.it% decrea,.-el.
4lithough application of the 850.in advectile Irchniatite to suutall storin. cs-tns valid. small intensityi
lov*, that htave ill-defined temperature and flow chtaractt-ri,-to-. touetiitlt- incream.e their t-irt-tilatIioit 5 or
(p titne!. %sithin 30 hours. More mature sttorms have stronger tt'mjw-rature antI %intl field,., therefore thefollowing rtules may be stated:
1. TIhe 850.mb advective measurement is more effective when alppliedi to eclones of large initialintensitv than to smaller lows. It seems reasonable also that the energi reqluiremtents tieces4sarl Iodoutble the circulation of a cyclone of intensity .5 %ill not be the salute as thost-e needed to) tolotle a
size 201 stormn. It is possible also that there is an inertial piaranett-r ishich i- priojoirtiuual in 'Amtne
er Ito the intensity of circulation.
2 . '1winitial intensity of the cyclone is a paramever in itef.
:1. C iclones of small initial intensity will not become major. intetuse storms unless the character of
the 3t0.rtdi trought andi assoc-iated termperature field is sharp. well marked atnd rt-Iatiovel!, strong ingraient (tor potentiall,% mo). If the 5110.ndtb rough does not exhibit these chaaracteristics. iii. %rtak
94)
Ce% cicuic' 1 iIl Ilect el. 1 .c i~ I II t Ia ll It, ilse ,1trin ele'spcte fi era ile clli itjIcli' at I850it4 ) . This resultis ini arreellclt aitl Alv-tin )l V- ) 114) folliil that thle- delelealenut ecf 4ci elotas is niaailio a func'tion
af high It'e piia ramters
As a possible' a'crollary to tlit- rule almole. the f Ioieiiig %%as nlie'u: all cocloiies iitli large initial inten.
sit i coun rts nict flie, crit eria o f roetc 3: thecre foe rctIlit-m- crieria ram Ii'c le'ii oe' c in fo reca st ing their develop.
mlerit. ThI'woation dael illtlliiti cef Icc Ici i eli d 'etiec ar- ftl e4t iliclatecai cf their future dieveleopmnent.
lTe edjec'eti foeceast ing techaiec fc r de''elecpttenat ofeC :ate'ger 1%* vc lenes is based cn these
three ptliuits
I . Tlhe intil i tenlsi t c f flt-e e'iretihtin ri, a parameter ce cototi toc, all stoirmsi.
2. Thet low~ Ic'. I (854 -m 14) d~hcl i e' ei neduccr aien ts gie'- flit- Iw celtia ramvi'ter fe r pcredeicti ng dlevelo p.
merit ccf high initial infensito '. tcrils.
3. Thle high le'e ci100nb pa44.111 lramaetIers art flie, best inilo r.s ecf flie' faa mare dvc'' lpcrcae nt ef c% .eI cne-;
with lowi intenisitIi at tflit, hteginnling elf the forevast iterioce.
t.; o JF:ct'tv; f-E 114 %tl pmt TECHItQUE 1FR PREIt:uCTIN D;ttI-A e 1AWN.tt<NT'
(:oni der lelt eff~ort %.a . e'~i'eed iii eo.ecocmng ccijee'ti' nirle'asiire'' fccr flt- e cfiniion ccf tfleit-~ c
C. A phase relat ionsipj ecf tfleit- %ina trocaih ant] tile thc'rtial t reaigi.
The "treouagh slidrjcnes- i.% iprciicer1 ic li I fcctlie- a'v '1 4lt'i vi rca'dtic 4 .atrc - [lit- trotg cli t~le- at ft liaIi talet
of the icirfae leow. It is ticaseireci llet'iidicall It% rtarking flit- trccgit hinte, al t, latiltitle ocf tilt-' sarfae
low anti neasalring 14))4 niile. ca-t andl iset elf flic, trocaghi line at tile~ -amal latitude *-e I ig. 11eA, lT'e iaiglt
difference in feet be'tmoeeni tit- ex'tremae ijestenti iceint and fiti, trouaghi lilac i- acldlce fc to e' Ilicbighit lifTe'rtc'nc't
folundl simtilarll 14MO4 ililes ea't. Ti i m t~ i., thicoterrectede fer latitudcec li-ing lte tabcle ill %ilpenii V.I
and is (if-fined a-, tlie 't re cigi sia rlcne..' Inc r-e n'e'. %4- c I . a hg lire p rc j r1 linl Itc fte ticorth ii ce ii 1 dent
offlo 1)wei st af thle treouagih an falt-e sem litacecmponeain at vast af tile t r cagl. a ticl %i enl adtied cl t et be. thle ret'-i t i ai
figaire be'tccmies jlroltoertionral toel fsrengt (of flit- c'i'lclie virrallatiour at tlit' St)4'tiic troulghi at flit- latitue
of thet loIw.
TIhe stre'ngth (of elft- tetiilc'rat lire fit-ie] is flit' pcarauter preiccasic llse' ill Fig. 4a2. It i. dtetcramin It- i.
swinging ant arte on fte 34))-mil chart frct the 1 celititlt elf flit' sairfaqe hcw. ven'lter 14)) maile% ill ft'e tnorthiwest
quadrant eof tilt leiw (Fig. Ot ). Th ll d'axiail tellieratulre ehiIfe'rt'nc bet im- f'lit i cesit itt ocf flit- lecw antie
the 1IWO)'ile art' de'fine's tlie' strength eufthe termice'ratiire fi'lei.
Thie tird plaramiter felr tlie' 54)4.rb icirface is analelgelas it tlt' 851).nul tt'e'raftte fa'ttcr adae is callede
the 54)4).aa tt'tilt'ratllre fator. It is foundie hay againi mtarkinag ft'e 51)(1)-it treoughi at tlit- latitudite of thle
stirfae ' elelale' antI nit'asalrirag po~ints .50) inile'e e'ast and ise'sf l tiefrocighi at tile same latitudle (stee Fig.
65). T[he terioe'ratulre differenie bcet wteen tlie, ex~trtee wtsterrn and easte'rn Ipilits is thlet' manaiitialde taf til'
torul hMra lire fat' t r. IThe signI is eetertminede I% neating 14hivh c f flit'- t'nl r flare'- is f lie' ecoldeltr. %t 141 las sun
is. icrefiked if tflie' coiler te'raliaeralItart' is wsest and a riegative sign if fte uis eter air is A4e.st. 'liii aiiaslireaaiti
Ills'
uiE
Q --
'I L)
u~ It
Lo- M
Ul +
01000
0SqqL
00000*
0000,
0400',
00000'
.0000,
Ea~
00000'
E~ -A
++ 200
F.g. 67.Th 850-mb advective factor. .4, i- denoted by X. 'The line IIH is conntructed 3010 miles on either nide of N such thatLVf ins ormal to the flow at X. 'The height difference DH1 (in feet) in found and corrected for latituds of .4, by use of Appen-d ix V1. 'The i ne .4C is alIso (J4X) miles i n lengt h a nd is construact ed perpendic ular to4 1) B. The magnitude of t he temperat uredifference from point .4 to Cis recorded. 'The product of the height difference 1)1 (corrected) and the temperature difference Ait) C in dlivided by the total distance of the surface low ito N plus the distance XE. (Note: the dlistance XE in the meridionaldistance in miles b~etween tile latitude of X and the latitude of the surface low.) TFhe quotient is detined as the 850-mi, advec.tive factor. In the absove czample IDB is about 'j4KI ft and .AC is about 12'.
depends partl% on the phase relationships of the cold tonguae (if present) and the trough. and it furtherindlicates to some extent the, strength of the cold tongue. T'hese parameters seenm to give auleaitiatc definitionof the 31N).,nb trotugh with respect to flow~ and t herinal rharacter. A~ compojsite % iew of the 500.tilb measure.ments is shown in Fig. 66.
T1he paranmeter chosen to represent the strength of cold air ad'.eclion at 8510 utib needs considerableexplantion. In an effort to redutce confusion catised 1h, large imnbelrs of iorkitg graphs the 1srtwes liabeen reduaced to) several mneasuirements and several mathematical mnanipuilations. SWhile it nayv seeminvolved, in actual practice thle arithrneoltvil uoperalIions will not be opi r1, cuminbersomne for a forecaster workingagainst time.
The first step is4 the location of the area of-apparent cold advection" and of the center of gravity of thisarea, A., as described on page 93. Once this center has been found, a straight line 600 miles in length extend-ing 300 mriles on both sides of .4, is constructed so that it lies normal to the contour flow at .A,. D~etermine
102
N T %
T~ Y
I-
0 0 0 00 -400
N 0 0 toz
(133:1)~~~f SS--kVH W£~IL 0
301.t
3O.A 100
80I
0 70
U
z 60
U
410* 0
30TALITEST
0i. . ltenii .r aa.tae . Itr e mjjlitn ti. h l.io n th ai.'rmreiin th rmnt ,th
tenwatir ii a.I .mgmh r.I ae t.am i iemrem ndh i. i.. iirUeti h ih n~
th egt ifrne nfe lc er tet reiaisoftebN)nielne liisdfeecei2hn0orce
exrmte of tha 1in is determined.
Two. v4 nrales hare now beenr obanfrA. Ene h la valuet, opo -rioal tod the windflo ae-ndn one piroptotnathe ldtemraure Fgr 1)adin r therd.Recfowd t Thshieormer usilt'h~ aver-r oteigtlns
lter heigt2 derees infetgre A the frteation. thes twomil lnes arei dnifferpnie and then forecter
faovi the esultA as represnting the trbeinho tpenix VrsIsThe rntin lwirguprent prootiona adton tl
thepnt offoAr,. dsee tA(i.)
1014
%c' I i v s% lo p Iit' ilet it itt iogi Is h I nio dou Ii lo rett giizet it I lt tif - I i itit - ir ant it t ier thait It'ross-i~o hi er m
flovo (t'i ld or Aarti) ia c'o nsideirabIle 1 ta ring oil ie i lit' unt of v *t % i coit' s% -t etis. It set is rea sonablie
to call ton nplitt e-Jierit'nt't iii itt's ltpilg dii- ideia ftirther. 'Therefoire. it ;s a-,iiet lbtat for dltepening
to tatlir there is al tittitlnl ditaiute frotm the t'~ tlonie for cold attlectili .A tik dlistanc'e (fromtfltl- low
to A,) inc'reas~es, its a ffett I ol in the (Ieet enin g o4 t h I I ie i s. Fin pr it I litI de're a es.
A !-ettiit factor voitds reswt'lto tt' psit itt1 of thel 1ItoA auitl A, i- t heir relati'. locaat ion on tile- map grid.A ga in c'alling )tn expenrie.nce. it is nifina k rtecoignizedl that thet mot? acti e ttriing occueir- Aheliti thie ittit
ent -.i ,thitrn flow1 is taiking plate tto filet wetst or siiti4ef hirtlier. a- thlis appiarenit aottIettitin mtIes
tt a ;ooitioniti mitre to tlt, stitll of filt c lelont. thet stoirmi ii-italt attains4 mia'iniitl iiiten-it. a nd th Iwtt'ten.
ig, dec'reases*. Recotin filrgte pos~ itin of A,* relatIive tfile 14v t1 i iili be l one it ti* ithI a Ii netar nea -ijre ment
anti a i anle. ti t iweIt'r.tii %o5 c4ttIttallme netedtess itoin I'lita It in ii thet co4 ill alt in . lii *teat .lhr iii n a
dita w in st aIfute mliles lIset % eeni the latIittie of A,. at I Ilte liti mlt' tif Ithe -tirfate lii,§ i- -iI titim,tLt 'A~ hien
A, is at a tatitiuidt north oif ft-e lo%. fl4'it- i-tane is taken a- zert.
c.t'clone. ll%it I lies. tif tIhe Ita ra mielers ha' %te loviin 14ti --Itt I ed m 1 irica I I % . keloti'tig in itiit iii thei t et' in stui
as t i r t t mn a t t ' . f i t - it ' 1 i' g t l i i t ' s t i ' .t r g e t i t j t 1 4a r i * t t i l t r i g h t . T h a t i -. im r i % e t i g h t i - 1 4 o i n a. . - 1 t r l i l v o i t i
loa111 initial ilittiit% than toi a stitrli voit t ahlighi ilittnsit' . (.inI tr~t'lf til t'e fouirth graphl tialina the
8S(iidi atth'ttile factotr as all orininate'. fit'- 14tigiiht' 1-Ip 4)14p11 tit Itlft titrr'it g1il ing: 111,M111ti1i1 %Vii11llt
'lTe ft met a-ti ng 1trof s'tire is tot tent er .'. n-t't tt ii lt filt' piarameitetr, in tile graph ;ijtiiwn the tcommoinif
to'-ft ire thle tend o f t.e t'rii it: terteftorte fill in~g qtnrig the Iatter liar? is not pI rectliudetdt. %. ait frietr aidi to
the' ft in t't' -ir. a tiashed~t I line t'itt ls at rii- It'e filial graphil anutdi differet' i ate- delt''tn in ig a il fill illg -ftotill
All stornis %hoset finl enltr% falls alittie ft#e dtashedt lint' vill lie forec'ast tti tttejen andtiIhiose bitliih will herforcast toi fill.
Thte matoinum initial inittnsit Iof a t'%loum i- atit 21 anid tflit' grapihs hav lt* e cu'i, iit tiff at th loo wint.
Whien a t' l ltnr's intensit I at foirei'ast ft l is greatter thtan :N. the ftoret'aste'r shotuldt a--ujn tIhat I t'rl, little
further dt't'1ining will ensue antd foret'ast a filling ttrittt'nt' for t'e e'nd tf tile 30.htiir 1 ieriodt. TIht coirrelIa-
titin t'tflit'ient between fouretast anti oblse'rv.ed initenisitie's wit reiet cotnsiittralil If li t I .tuns w4hicth
prtedic'ting 37 ove 27 is qinestitmautlt sine' a major stotrm will mvn'tit in e'ither tcas.
ilitng at.irm-o are itItse that have' an initial cmemin grteatter thani their mftensit at It' t'rti end 31) bontittl. '1114 a cti %ettit whichhailinitahI an intenpity to(21 antI at tile end tif the 31'hir tterim ad itl i"Awt f)t tlil-ti I. iiAitttlit'o clatssedl as a tiller.
OD N
+E
N +Na
+ +- -
kl~l)W~lRinlb~dV31 9Y 00 a.
l~OD
0 0-
___0_0_0
0 OD
_ _ _ _ _ V~ (0IJA3VS4OI
107
NN
NN N
N go
NN N
o0 -i MZ -
r'JN N V
- 40 f4J
TZ a
44*0P-
-
N 00
I L 0L 69'89 S'Dl VgO0zi S1IH'D3M JO V4r1S iz B
A lm et ii musizit ie ii liet raise re'gard inig d ie Sf4 cl enct of thle 1t II).ci t roulghi it ii rr~ cwe t ie) the murfae
si ste'ici .At thu.'. (hirinig thei %inter seasiol, lhe tiller t rotigh assocciatedi with thlie surface S. steli %ill remain
sa tie 'ii.% 'or ret ro gra de %h ile the surfae loI i nioe oi i. lIt general. this ewe ers idu vilin tle- 500.mbtroi gis it -agreal dist a glee frontu the sucrface Io%.w lio 114e er. ill thI ese casest lee a lsc~e mhodIe fo riecas~ts too
inich ii it eie ~i icjtie n. TIhere fo re, a seia rate rule leas Im-ellili dee I alnil shie in lwh a li lii' %h en tihe dil ta ne
fronti the leu to thfle 5( W-nib tcreouegh is greater tihanit8 110 miles. Tlie fo recast er shld mclneastire tis distanle
its a stanudar ni jroeduilcre w c o nti ig the 5Wt H I-rn jaite rs. TIhe rulec is:
A hen thie rast -west distance bet ween lte- 4lrfai'e low Jcitil and the 50N)-ib troueghe is
greater than 8(4( miles. thei values ocbtainedl froint the weight lines on the three 530t-mih
g1raphls (see Figs. 08, 09e, andl 71)) should bei divided hi. two befocre summing w ith thle 850.
nii) adi ectiie factor %eight value (see Fig. 7,1) anti jcrweecling to tile final graph.
If thle fiireivesler k niiws for certain that lt e .1(N)tni trecugheI will fadle ocr retroigradle. it wicild lee- adeis able
to redlice tihe fomrec'at miaxinikini icitensiti% ialeie a nioicinal amoeunt. It alcjwars that a few eof tihe "nii!.ss
(i. ed ii c thle fincal raicih) were duei tic tic erratlic moue nie'n s icf tie 54)11th featolre.-. Ulthlouiigi it i! no t
literticlehit ticludlee thle lineignesis ocf lice- Icicher IerI' trouighs at this lttle, it is ccrtainl.% nece-ar% that this
sheouldhli e inludedi bc as a c)aratieter inl feiture resea rich. Tlhei i ndlede n .lt test dlat a conn in g~i 33 ia -i' iliiri ci
lte' winit er o f I i)l 52 ' ieldeil a eecrriela tie ct- i'cie ct lire i'i fi cla m idi oe cd.' einxiiaicm inte tii t '. o f-4 ilhi i a ii a I eraeet erro r i f 2 .90 ii I. A sa njcle wAi rk sheet is lire cde on ie l ecija ge'it )for tile tim oi f Ilite- fo re-
ca~ter and c - ' also) as a stimmary icf the icjs'raionct whichii ul luelit c- fulicewed in arriving at the delecenirtg
or filling preegitois.
1.6. We I-A:MENT (OF C:ATEGORY IV C:YCLONES
Sicme icniclusiomns 'cncerning lte ntil 'ent ecf (ategecr IN"s ci clcs hia-i ibheen miae in a jere'iicinan-,
repo~rt on thiis research. Since a number of tile re'aers ha~ e seenc and ajcplieel ;carts ccf thles-e lrelitiinar.,
resuilts, it is jcertinent to remark that the treatment of the ediriectien icf ninetit has tierg'ei miajor
ehanges. The loart-i 'cncerned with spteech remlaint uncthtangedi. Coniidt5 a liilt-i iusi has again livenc madie (of
are'as of cross-isoitherm flow as a forecasting lcaranitteer. Theii rieader is again r'fe'rede ti age i93 for a dis.
cussion of the method of determining thle center .4
1.61. Speed of AMoltwnent
Numerous methods have been diescribced in the litieraturie for Icreiiit iuig the slicedi of tili icienit ecf
surface cieclones. Exp~ressions can be fein i ch as "$erfae licws sile it i(ii(P) tic8(4 wrei'lt icf tlii- 700-111b(or 50)Oirnlc) flow over them." In case icf iilent 'cntoulr fie'lds ecr closede si ti'cts icier tile semrface ventier.
the ajcplie'ation of these rules becomes dliffiult. In thle icrice's if til' inivestigatiodn. it was fcundti that lows
which are far removed from the center A.~ generallyc move faster than lte lows whiich are located near it.This seemis to vecrif% the finding of Geiorge (ii)IQ) that lows tave a "jcrefe'rreel jco'itieic" witli resjicit teo tile
thermal and icressuire fields, and that licws whiech are some idistace froct tlii area icf inicatede warcm aevec.
lion tend to accelerate to a position more favorable for continued cyclogentesis.
The first oblservation may be stated as folows: the sliedi of lite sucrface eie'lone is roughly prop~ortional
to thle distance ce'iween the luiw center anti A* ... ( )i the basis ecf lite' lcrueeiitg stateme'nt. ione' %ild assime
Fiat thle steee icf micvement of .4. would ha ve all effiet unl th slisedi icf tile stirfaic' low entelrs. It is
bit
WORlK SHET;i FOR( CB(ATIEGORiY IVCY LN S
I NTENSITlY
D)ate Time Surface Chart T imie Um'pjr Chlart
850 7~ 0
1. F'rom surface chart findi intims-itv c-i mit of loiw. (Ai eriagi dii ItIeInpiressure Iietusern center of liw andi thr fiur cardinal ilirection it'At 1-i11t-NM4) miles from eitter.)
2. Latitude of the surface Iiw. . ...
3. Trough sharpness. (Diffrence in height in feet at the latitude if low lie.tween a point 1000 milesa west uif the trough and the trough plus the differ.ence using a similar measurement 1000) miles east.).
4. Correct (3) for latitude .
5. Maximum temperature gradient 1(NN) miles in northwest quadrant fromsurface low- - .
6. Temperature factor. I)iffrrncc in temperature at a point 540 miiles
west and 500 miles east of the trough line. measured along the latitudieof the low. The sign is positive if colder air is to the %est
7. Distance in statute miles from low to trough along latitude of low.
8. Determine position of .4. and record latitude of .4,.
9. Construct line perpendicular to the contour flow over .4,. anti measurebeight difference 300 miiles either side of.4.
10. Correct (9) for latitude of .4,.
11. Construct line perpendicular to (0) and measure temperature differenceat a point 300 miles upotrerm anti 300 miles downstream. ... ..
12. Multiply (10) times 0 1) ... .. . . .. . .. .
13. Measure diatance from low to A... (Statute miles) ..................
14. Measure meridional distance from latitude of low to latitude fer .4,...
15. Add (13) and (14) ............................... .............
MI Add a.b, c,(or d) and e......................................
(g) Forecast mazimum intensity from final graph .......... ... ..
COM PUTATIONS:
I ~N,
tJig. 7.3. %% Ind comtmne'nI. lt.r g-tir-pic %ind~ niia-ir-I .mr"- i. .ing N fi~tiijh 1. *-ii n-pri-et. t.% titi
ii,riiul I., iii. tine frmtn the lii.. 1,, 1, anmit iiig III,- %.mdt .ip.ni-im a iii w.) b-iIrreviii- I.1.% 'li unengheight tine..
rvas4, table alt t oIo a--ni I I tatII tes .et tif -1, is protlmirIt it itIa to t ic ratic i of 0 fl A t I..I iisrter. sim-e. thitlow4 itidit, tim t tio% ttartl A_, ouu fte etiliiileit ilt4ii altin, fltil line fromn il lti tmit) I teie lit cnsidered.
T he ,.tc'id obI siterlatin i:tihe spee oft Ihe t i*iirfae ' %c limise is 4 1 ro ibirt it 1.t ii loie tctompliiwt ofit flow
at I V, Mlom the linec l6etiien ftle IIIi arid A, Tlhe third factolr relatedl 1) sped is n1otet iii if1n4Ibetitin of
flit thermal field at fl i 3. loter st and a rd siirfae. A lhen it-e isth ierms are- packed i a oig. in le t rackL. ft iir-face It,%~ miie,4 fast amid %d ien ft- tenlit-ralure field is %vtaL mnid iduering. Ihli- nhit 1.41%. Tlhei %treigtli
liast eIfimrts ft a..iiiate ft le d ofe ii %% it tii- itl loplwr im it hai e iieen Iarget'ir mnisvesfl ( Paliiir
l1918) iiee4aist' (ift tf ltit eesiti for choittiig tlit- itini at at 1 articiilar spitt. ii niai vases. tlit, niagniiiii' of
fh itid ljwctl diiyle.- radjeali' t.'.er f.,ir'. 'ia'.rt dilaocv ie' anti it %ioilil be fo~ritaitoti. if tiet# correct value'.tcrt, e'im-ei. hlowe'. er. inin he'.a trilg fie ..treniii 4of tile, teltt1 era tizre fieid. lte- magnitude of tile thermal
V.~intfl ct nen"'lti i. taken intop acciint anoaial..gin iti nitleiiare'o air lranlotsl r r a considlerable
s.oitnije. anielitilg ito an irltegrata..ri of the %.inie effect.
TIhe third tber'. .tioi i,: Ow t'.rve'tiof like- siarfaiee c .% 1411ie IS propmortional to lite- strength of the tem.-petratt ire field.
Ili ?-mmniiar% the simet oif ( att'gtr% 1% cicoiies ila\e heen shit.'n tit ibe eiircctIl proportional to the
2!. The ftretwili id I10'.' t.'er ..
.3. TIhe stre ngit (of the t herm fiii rlde alom lb te track.
Thet fir't opeMratimit i. to) determine ii. ltwatjtim iof A. at 8.)j) tIII). r'iht' ala-tance in '.tattute iles. between
the .urfat'e It,%.' anti A , i' the lirst parameter.
The !wtom p nljarameltter is. the~t tttntilt'lt 4of tihe geo'.tropiiic %ind at A4, in kntits along thle line from lte
it.'.' to) A, mwe Fig. 73). It % a- foiunl that thet llll.t tim-fcil metasulre of thiis vlaite is the sunm tof t hese corn.p4)lellt s at 851) and -IN4) inh. Foolr tii nlea..tlrreilt tilt ilot-ititin tof tiit# 8.0.nlic JI.u i'. miarkedt ton the 71k)4Imb
c'hart.) \t'gata'.e %.alies tol this etllllotmett are ctntelttt a zt'rf. This. oo-vtorrs A!en tilt' pti~ton . falls
itilin a clt..eai lI) at either it''. it i'.. lhoisever. e'.treil,% rare.
Tihe third plaranmeter ha.. alreadl l'tl tlbee "dtsribitt n lte stetiton ttii tie'.tIteflt'flt (p. 99 ). It is the
ma'.im tenlherattire thifft'rent'e iwtise'ite 1;s i tion of the '.urface It(',% anti a i 1)(11-mile are in the north.west quiatdrant front thiis p~ositaon (stt ig. 0.4). li lt' .1411 at 8504. 7W)4. anti .501 ml11 arte atidet ttogethe1r and
tile stum is Ilseti as a p~aramleter.
In stlmmarv, the following parameters were selec'ted:
1. The tdistance in statute miles from the surface lmw position to. the center A.;
2. '[le sumfl of the components o~f the geostropilic wind in kntots ton a line connecting tile surface
itow to .. at 71X) andi 850 mb.
3. 'T'e stin tof the max.imuml templeratulre differen'e, in degrees Centigrade. between the sturface low
pttsition and a I000.mile art' in tile northwest quatdrant at 850. 700., and 5WM nib.
'Te obljtettive p~ro'edutre' in determining speerd is tt) enter tile valties of the above parameters in thle
mutiplet cotrrelationl given in Figs. 7.1t anti 75. The ptrocetdure is:
a. Enter alontg the ordlinate of Fig. 74 tile tdistancet. (1) abo~ve. an(I alo~ng the abscissa the temper.
attire sum, (2) above.
1). Exitract a value determlinedl by tile weight lines.
C. Car value, (it) above. to ltle o~rdinate o~f Fig. 75 andt enter along lte abscissa the sum of the windconhliontnts. (3) abo~ve.
d. Reathie forec'ast 30.hlour sp-ed in statulte miles per hitur frotl tite cuirved lines.
Fig. 76. tnnqtantaneeou% cmieteor otirring. T6.s iq generally taken fren e ir70(-mt. er 5(0-mi, Surfacei.al though the techniquae ali.o applirq te, te- eerminat ion o.f thle d1ire-ction cc ofe dlo at . %shich i% 850t nil.The inctantaneceur steering im the average of the dierecteccnm of the tangential liii,-A at .A anti B, the dasheiline being normal to the flow.
The solution is not time consuming anti the entire operation can be accomplished in 5 to 8 minutes.A worksheet is included on page 11 )as a guide for the forecaster.
In previous preliminary reports somec explanation was given to a special type of cy-clone called a "cir-cling" type of storm. It is felt that this term falsely implies an unusual trajectory and therefore the namehas been discarded. These lows will henceforth be termed "Special Categor * Cyclonet" and the forecastmodification concerns only the speed of the storm and not the direction. They were also discussed in thesection on cyclogenesis.
The special category cyclones are usually of high intensity with both contours and isotherms havinglarge amplitudes. They are defined by the character and strength of the thermal field at 850 mb as; follows:
A special category cyclone has a temperature field such that the amplitude of the 850-mbisotherms is > 130 latitude and the half wavelength (east of the thermal trough) is < theamplitude. The "ribbon" of isotherms associated with the cyclone consists of three ormore 5-degree isotherms.
D4 %N P 141 I It IPO
)II iii. "in, Ito Iar i- Air
S11' I D:
I. I -.. at,- I -it ;t_," ivii, iand tr.ai:4fr j44 n 44444 , 1 ., 7,01
2 i-t.am c fr,on~ 1,.% 4. 1 .4.44, mi414-I
%I. %ono 1, Ili I., ra I or,441,,T.444r !I.44144I fr.i j rf. 1 I. in444 aaIl rin t --
ra v i t
a I ..... t..~lo- ii~ .m4 -- n imao- i n4, Owlm nn1,
I4. %.Idj 4 '411 In _'
7. Hr,-r %.Ana - in 2. I 41 4, 6 .-.. w Iow pap"114 G. cm, .- t 1"4 4 I11
14 (.I,-, k aiitmai... -.. 4i-Orn,, fr.- .1a ca-u 4-4 44-%1 1--v If .4141;14444411 I%
SIf -4,-i, 4l wn4 4444 4.iffi la 4.1,4, ilt-tt~rnmw at4 7410 and4 .7,~40 tmiI and44 the
I. ti-rd ii. 44444' 444.111-m-fa nd Ill .141 . .......11.1 v.' m -n I'l 444 I me 141'j.41144 g 4111' -air.
f4ace 1444ls vvn4'4 4 isth On, v,44,f r1 ,. -
it line4 a,miil-4lig the .lIrf.vIo an44 dal fll,- 4-voilcr . I , mill it lIII%- r.'.4=itirc-ing tilevoutou.Ir I],.%% at4 I. The' hi~jv4Lt is, the. Im. oIf fninre'Il ,m u44li.)
%II;l VII FNTO
%'11\11161 \1 IN H NSIrY
600 MI~ -- 0 M
A 0 SFCBA \ a- LOW .01 5
Iakn- hf ti thr a fis Idrs. Ti r akina-sir c.551 ris1- s- id i.t) if tliV~Sn t t r ii cii Iscr t iii. it ns
stormas. Fosr tis reason, it has- been fmsnr that idreit a Irn fualfill- tit- rvsietrvint-i ss(a -jso-rialcrategory
cisclone a oaI ire of osne -ItaIf sof tit- ustira I fssresam-t -I se-ti Iprso( I kit ee- tI ics Ise.-t resti It s
1.03. Dir.t-:itn (if Almmsent
It Itj belen rt sr-re ft-s isoin ie l ite that till-,~ i tt a nesm sr T 4 -mti c st t ir steerng iti sier tire- srfac-e
l.iI5oit5 l5is itiist ttl ti l~la . e- ita rcni-iiail acittrae itdicationt iof iii fiaitre intsiest. Tis psarameter,
-iin intJg 76. ha,~ thters-fnn- Is-ett inte-gratedi irili tirt- osijestiis% -lirt for all (of tilt- ( aegrn IN' s-in-Ines.
lirre are- Ii iitt. of sr il -s. % I-itr it i - sliffillitItif tsr ie d-tIt- le -t Icon tour sit -rintg so% er tirt--tanface s-vt-lone
(lit- to) riiflrris nsof Ihe field aloft tsr ii ihen at-i spsed I i it t it tttis it it tt- oier IteI sttrface low5 s-euiter.
lit ca~s.. likse ~tese, sir ihent 11itsre i siiis doub ts t ilt- stresrinag. it is ash im-aisi tso .selecst tihe stecsrin-, direction
at 5(M) til.
It Ihas al-sr lis-elt 114,ti4A that tin4- orienrtationi nsf tilt, i-stiertt fil is imptoirtantt iiitir regarid tor tit, frtrre
track oif tilt- -iorfais- q*et irr. % ttteas~ triti it ich it art ial, de srflines~ ihi o rienrtat I in iIt- itthiraved in tile
d ims-t -o-sitn ofi I-- oiti itg an tsl li.. I I is tilt- 8104-itt1 isttmprnatturs- facntosr (p-cc ig. 77). an ts inie it is a iras-
tire sof t tt is-ora irs at s-sinta dsi ttancs-s acs-rs t itt- frsstag itit- amtp litudrse an tti t -Isigth itof tlit irs-rnr1% are
lpartialli dinied. Thalt is. foir tit shoirt iti els-irgtti i Iis i aias of tit- 850-orhr titje-pratre fac-tor will 1weismiall Josiii - osr ittgairt ii- antd for lilt lasIrge- % im-legth Ir tsl- iaitos atre gs-israt largs-.
NORTH
+9
+8
+7
+2
-40R LESSSFC LOW
Fig. 7M. Template for % Ulie., .f It I -r nil ritilii ttre fai. t. r < III 'I h, rnter lif the template iAplaiedI on the Piurf ace tin. l-l4 iG %itli dw %rrlicdIal' ..i,,m Il i, rIrod thlrqig thle tion center. I'lefofirecti l u itdr I ltrroniowd1th Im, 111 r. 'I i te 1,- -1r I-, tic %a.~s~~ lu i,of the 814t-mh tern.
Ileratlire factoiln tile 1w-ri1,Iif-r Ii, 'Iirtgrim % .llli-ll III-, lin-. ,~ gl%,li in talmlaar forma on p. 118.
It % as feiUne thtat leaWS 14111) -mIlil it wi' 4)r tiegat ii. i altar 'If 1 lic 85oh ltlatuntm-rat tire factor tend tohave a tuore doiminant eastrrlo, cni eit it)a their track. and ci clonrte % ith large jlsitive values had amore neartlterI% compo~nent lf ieation. The %ati of the IO11-nil, temperat lire factor has been c4)tttifled with
the instantaneqptas 7tWt-nil cecteatir Ateristg ocaltr tile III14 center toa eleterimiuc' the. feture direction of mocvetment.
After tile valuie of tile 850.mla temptleratuare factoar has ben determiuned. the forecaster proeedes according
to thle magnitude of this %aheae as follows:
1. 850.mb tern jwratre factors < + 10. S- sterns eof this t ile generall * hta t a large easterly complonent.
The tenmplate, Fig. 78. %as designed cinjeiricallhi attel valties of temnperatutre factors fromn negativeto +9 are marked on tile lwrilller% o~f the qeiuaerant. The table iii %pj-nehix VI gives the values
of ties' sints in dlegrees e'ast oaf noerth andi maa be oused if loreferred. Thel tempalate is placed with
tile center can thte looiasitiime eof the searfuehac 14P %ilt the 0' line placedl along tile meridian titrough tile
low1. A dlirecetieon is then ele'rttinecl 1) * tihe center andi a poaint eetrre'spoitilittg to tle tenptrature
factear mtarked canl thle jeriphierv. A lute' is edrawn jeointing thtese two poiints. A secondl line is drawn
through the low cente'r 14 Iieb is the eirectiont of the conhtour steering at -,(X0 mla over tite low cetnter.
The angle madec b% tile twe, lites is laisee4teel anti the bisecting line gives tile 30-hour direction elf
movement. An identical anslwer tan he' eobtaitned h% lise' of tle antgle given itt tile table berlow.
T'his anigle anmd lhe 74M4411. iniit crinmg amigIc (mena otured. fro oni orth) are a vera ged andoo t 1e restill
giv~es thle 30 -inour udirec timon oaf imanent.
I~ tn
44);
2. ~bnhtemnierature factor > 4- 14. As see n in the earlier section on development, large values ofthe 8.10.mb temperature factor generaII.% indicate delienimog. These storms haie a dominant north.
eriv cornponent. The center . is utilized in forecas'tin~g tihe dlirecticon of moit-mient of t hesec, clns It %as stated earlier in the di-Aisionm 'of sliced of mbovemnent that 1014s tendedi to he
directedl towardi the center A. . ando t hat the inooiement cof . ha-s a coomponent in the direction of
thle flow4 at .A . Therefore the low1 its.elf wiill have a coiniooneflt in the direction of tihe flow4 at ..The direction (of coontionr flow at .A * is meas~uredl on lhe 8 50mbi chart and is. combinedl %4ith the 7009.nit) instantaneous steering ovler the s-urface f)14 1isitinf. The angle determined by1 these t141 lines
is iseeted by a third line whiclh is choso~en as the olirertion of movenhent. TIhere is one excepotionto the above procedlure. 4 N-ainl . wille iii the lieri iiery oof a clos~ed loow or %4ill hoe sit ja tedSUCh that thle floow at that pooint is ie~t oof neorthI. Iii va~es like thlese. due neorth iihoiduaIwht arboit rarily
chosoen as the dlirec'tion (if flow oover A.1
1.7. STEERING4~( INDETEJINANT
On seome ofccasieons. the steering eo, er the surface low center is i neletrn imoa ble at both TM4 and .5k) inb
(or tihe directieon of flow1 at A. is diflicoolt to dletermiine delii t~o ihiihuiemoce or 4to e~tremely wea k gradiemnts. In
these cases . thoe jrot-eoure is identical tao t hat just de-scribed excepot t hat a line joining the surface 140w and] .4.
is substituted for the 7444-mbl (for 51)4)-ijih) steerimng ocer the surface low liositioon.
Vse of the aboove metodms ion IN4) cas.es' of ohejoenlemit ihita ill the 14imters iof 14W) 478. IM) 141). 1010 10.
1950- )1 ' irided a correlatieon coeflicient eof .11. Thie test oof iuileleneent dlata c'oosstedl of 33 cases edurimng
the winter oof 141151 -52 % ieloling a ceorrelatieon coeflicient oif .72 and an aiicrage error cof 93 degrees. A work.
sheet. fion page 115 (hootteon portiion) is inelenled as a guide for the forecaster.
IN'~~ F* 14 ) )1;C It,-
Ivtcitatke 4ihliq itii~ i tilt, erobleleni tif forvic.ting lit- feature 1iee)itimie oft antiec ci ncs for 2 1-and 411-hour
jce-iiel iia ecoe reacihedl. Tii -.eeiiititiili/'- tilt- Ieiiii jat te-rn at 810 Fill) toe determine tilt directionoit iiitcemlett aned a owe~maoein %jind locede jearalieaet at 7041f iniit) determeine si1eec41i ce itflen~fieflt. Using
inelejcI'iaeli It iel ata. II it- a% erige 4-tteer iii p -,itie it I-a 24eii iil feet a 2 t-liecr jeriepelI iii ) I O iiiI"~ for a 4.8-
hoeur lwriode. In tii iiea~eti!_aion. a total (if K.7 ca- %sere talmilateil tier tilt, fifteen %%inter niocnthi, (Necll
iet-r thrietwl Ma~rch) oft 191- tireeigh 19.7)(1 fir %siiii track- 4 at lea-I 18 ilielr- couldl III. iiitaiiedc.
InI ill% -1 i ,alii i h e -eriwi~ Ief c, Iel anit ie 1,lee11ic- %it h tile- 71 I-inhi lo%%l, ( ;ecrge (I1') it)) fecund tile "iso-therto rile~i*e tII Ill- if 1 wiciai .ipeiiciaece. I .iii, t Ii 11 a teaite caa-. in tile- first twite %ears oft the
saniet p eriod eelsvre ria,--i lie l aicco rdling ice tile- lmci ie en o f tlte -erfai-ce nter reIa tive te) thle isoetherm ribbon
at IN) mue andi at K:;tl) fill). It Jvel,,Im fl i t t i t - ii-ihiatijun rc-lati e tee tilt- 850nhe isothtermu rilihon was
rater clear-cutt ani '-iie ile. li .-A edit oef 51) i-I-c fallie, iittie focur grieljs. Tecntative- A)tiatioens toe the
proemi 14n if li ree tie n e if nei emeni lt we rc e eie c fC er eifh eof thle fo ur It. Im-,. Tlhe re-sult ing met hodls
11M,~ liti, 1 -ii t te-cli li, lie cit urlfae i. K51t- andii 71 I.On iii n a je i.e..- all tire gni i,-v a re madie fro m current
n't iic iia t ria I am pi Ija t pli!i tici- d rt* noit (c onidiered .
m12. ~I Imtm ot e .%Nrit1c i ie s
1 .21 PIjrectiwie cef 11(mirtieft
Fier-711 tir' cui 82 -heelS tiit- teer lcaic vla,-iicatiens (if suirfa-ce lhigh ce-nte-rs relatis e to the isolienn
ril il at the', 81 I-en stiltface. In.pe 79~~ ). tilt- anrt u i'c-oe i ocat iel in the iso t herm niilei en. istiali i
it it%, tis e euIce 5' 1( i-itieri-re iecithie-r sie. lle .A ihighs inoec parale-I tic tile- iocthirns cit this "snap.
shoet iiitoe"- tier thei first 2 1 hecicr- anti -Ii,,htl% ticsarch %sarne-r air during tilt- -eceomel 2 t lieuit. -A) that thle
path ileririg tilt- IX-liccr jeetiiie is a snmoothe curvc-.
In *I)Il It 1 ( Fig. 11). the antic'' elcine is liicati'd seceth cit the iccthc-ree ribbocen andl west of tile thermal
troiugh. Its eI~cficipe-eee is iletec t lw isethettinibo iciii on a path that is parallel toe an c-~tension act tue isotherms
east cot tile- thtermial treieegi. I n nii-t T.s Im It cas-s it was funde that tile track tier at le-ast thle first 2 1 hours
%a., abucet ilie-ncliri-lar toe thet- 8501e -iti c teccars. Thlis t- li ofci high was feound to lbe mncst conmmon to the
Trc- e stern Goelf lif Nlc-icii area.
'Fujie c highs (Fig. 81) are loc-atedc north of the isothiernm ribbon. The mocst common synoptic situation
for this t~ pw is when an antici clone colmes into noertha central Unitedl States fronm tile Manitoba region.
TIhe highs moeve across the isothe-rms towsardi warmer air un a path generally paralle-l to the 830-mb cotetolirA
bent with soieee- te-ndency to c-ross toesarci higheer numbie-rede contoulrs. As in I'~pe A, the track is uesually
a smothi c'urve throuaghcuct the l1.Ieeceer iwnieiei.
In T% lpe 1) situatioens (Fig. IQ2). tltl- aefite-clonte is lcatedi north anti east of the isotherm ribbon, with
applarent warm adeltion tic due- noreth. A t% p icil c~aeeipli of thuis cotnfiguration c-cuers with a surface high
centered over tue plains states. a cloesedc high or strong ridge at $50 til) over the Rocky Mountains, and aclosed low at 850 tub ove-r life Mississippii .ealle% secitIeast of the stirface high c-c-tter. The track of a
Tyvpe 1) high is iie-riveneliv-ilar te the thierimal treough and generaly palrallel to the lte.t)-ibh contour lines.
Fig. RI). Type A: Surface high center I,cate benth the 85)-m i,,therm ribbon. nI t ovf th thr-mu trolgh I thrme to the ri hours awith wc a Plgh rtenynof ath iarherai rng the ther. :
ma ouh.
i21
SURFACEHIGH /CENTER L 0
//
7- /-~ 24 MRS
-/
850 MB Z8
i- 11twriv t,,% .ardJ % .rit 'r air m ao .i i htJ : , ,r.i11% pa.rall-, I I,, di, ,qll, r- 1,' 1 ,, rh ' ,.
SURFACEHIGHCENTER L 0 W
S /W
"--.- 4 HR
050 MB
Fig. 8. rvlw. I): Surfare high (-enter Iorat,. north anI ra. ,,f the It,4).ml, imrtherm rihln. Warm ad-vl'etin ii apparent ntorth ,fcentrz. It m. vo on a path ierediwluilar to Ihe thermal troviugh and approii-mately parallel to the conttmir lines.
Io cases were found in which the high ceulter was loceate~d umnder closcil iso~thlerms and contours at850 11111. 111 iboth c ases. the surface center renmained zearI stationery for .18 hours. A few cases % ere founidit) %is II th 1wClassifCat it'l 'As siierdlerline bled een T'l'j A and C . fin these cases, the track followed wasa coinpromise' direct ion btet ise thait of tile ~ iothernms anit that of the (' n totirs.
1.22. Speed of .oIelle'ft
A -earchm for other useful piaramneters was thlen initiated. It wait apparent that some relation exstedi
bet weenI thle sliced of the ighi and tihe flow aloft over or near thle high center. A~ prelinminar% ceck was
rimace tising Ithe (ibscr'rd eelin icceds at 7WX nib over thle high center. In some cases, this pro ied a usefulmneasure. but in mil% oithers th 1w -d h igh1141ed ('emsieleralblv faster tihan the observed wind& 4ier the center.This led to an examination of th w maximumn wind sjweed at 7W0 nb transverse to) lte culrre'nt fHow adjacentto thle surface high (-enter, andi finally to a useful correlation between thle maximum o~bserve'd wind, its dis-tance from thle high center and tile speed of tile high.
Figures 83 and 81 illustrate time mnethod of determining the maximum observed wind speed. The
-urface tXasition of tile high is- plotted on the 7MN-nib chart. andi throuigh this ploint a line is draisn 1,.'rpen-
divaular to tile conitoiur line.-. Ihle# first definite in d maximum that falls along this line is selected as the%alue to be used. Fi'gure 831 illustrates lt- usual case where a maximum of wind slieed lies to thle noirthi of
the high center. Thie mnaxitnum wind in this case is 415 knots. rhle secoindl paramneter. dis-tance from the
highi center to the 1oinrt oif niaximnm ind. is 6.2 degrees (If latitumde. Freem tile grapih in Fig. $5. a forecalst.joeed iof :31 miles pier hour is foutnd for t is examnple. Ini Fig. 84. the maximum wind slic.ed (f 30 knmots is
ineaur'd oler the high center (dis tance 0.0 degrees). Froem Fig. 85 thle forecast sileed would hee 27 miles per
hour. Note that in this examiple thle ioiiervei wind speeds decrease as we move aisa% from tile high elater.
In Fig. 85. thle distance fromn the high center to) tile jrnint of maximum wind is lilt tted as the ordinate,
and thle maximum oiacervd i m a lt- ahesci.-.a. 'The sjwoeol of the highs in imih for 1M hojr-. is ploitted
beside each looint. Th' distance, for convenience. has been expre.'sed in ciegrues of lat itude. alt houagh if
desied, a scale oif statute mniles mnay easily bie substitute(].
%;here doubt exists as to ishetmer tol use a value taken liver or nevar tite high center. or a larger v alue
taken some distance away from thme high center, check thle spierd graph JFig. 85)) aInd use thle oine that gives
the higher forec'ast spe'ed. If obm-rved winds are not available in aim area %shere the .pao-ing cef tile conitouirs
indicate lte nmaxinmum to) exist, a imicasureel speed may be used, but should be re'gardedl as ani estimate.
The following moificatioins shouimld be applied to the forecast spiced:
1. If time high center is withime 81M0 iiles of time 850-mub trouigh line, measuredI in thle diirec'tion of expeted
meevement, 10 miles pier houmr shouild be subtracted front the forecast speWed.
2. If tile high center is located livbeeath a nearly wsest wind associatede %ith a broad, flat trougj-h at 700
nil, use one-half tile foreecast sliced. (A. goped test to apply in deciding whet her to uise, this rule is:
if it is dlifficult eir implossible tei draw a distinct trouagh line. then tile coerrection should lee applied.)
3. In Ty i1- C highs situated in Canada or in time northmern United States. 15 miles lier hour should be
adeld to thle forecast spieed (from Fig. 85) for tile firtst 24 hmours and 5 miles per hour for the second
241 hoiurs.
41. With highs in the Roicky Mountains, roughly west of a line from Big Springs, Tex~as. to Great Falls,
Miontana, the speed graph shoumld be mused with caiution. although it ist still the best tool whmich has
been found when used in conjunction with thle rule given in thle next paragraph.
123
DISTANCE TC MAXIMUM WIND
SURFACEgHIGH CENTER
700 MB
Fig.9.3 11 t ),- 11. IL II I wil I fI fr ir ii r
SURFACEe HIGH CENTER
700 me
Fig. 8 I. The (I'114 %fri 11 Ilat uionuan im ni- -- rclt'tl tver te ant' titcy'clonel center.
- 10,0
a /10 /36 428
--9 -_ _4_z
x 33
/ / .40: 38 ,
0 29 / .29 46 "
44C 6 -f 4C _
W 146,- 2,- z243
.429 31
3 20 __ 30 I5I/I -w '-4 -5
*22tj 2 --0
z
- 228 32 331 42 33 3j47 140 1 1 52CO 0 L - a d 0 723 15 20 25 30 35 40 45 50 55 60 65 70
MAXIMUM WIND (KNOTS)
Fig 1t. Thr relation It,.t, e.n the antlivloq- renter. i.m .iatance to the miazinum I wind in the adjacent current andth, mazlcrmllnm .h,. The family of -urve, mrapuir- the Piubis-,Ulent owri. of the anticyclone in mile" lir hour(Ilarge" tigir-). .i nt'rakl hin iath lehwiltri- of anticyclones.
'The lmt-iln of the 700-nib trough line ipr.vd very useful in forecasting the formation of high centersin the, Texa.Oklaliomla area following passage of an mP cold front. In a typical example. as the cold frontiol-i., off the 'l.xas conast. a ridge front the near-stationary Rocki N ountain high spreads over the areai-hincl tihe cold front. alid remiains as a ridge only until the 700.mb trough line moves past the Texas coastinto the ;ulf. A ic.d venter of two or inre isobars then forms in the ridge, and tie movement of thiscenter call tIhen be predi'ted using the methods previously described.
1.3. INIDEPIENIiNT I)ATA (:EIK
Forli -4'illit c'aw%, of anti-ihclones dulring the winter of November. 1Q950 through March, 1951 were usedas an infh-loio-uihnt dala chIr-k. i)itanrc!- and spe-eds were taken on a straiglt line path from point of origin
to the 2 -hour imsiticen and tlhrnr on a straighnt line to) tie 48-hour i msition. In defining tie center of ahigh. the. cntler of % n Ieir was ued Ul. lioint of highest pressure could not be used since it was foundto ihift aioil fronl mall to inap sonetime ai muic'h as 2X to 00 iiles within the innermost isobar. Tables
4 and 53 sumlllarize tile results oif this indepenilcnt check.
Tablle 1. Ir.-qc mee4 cti-tireti i .cf q.p.ere -rr,.r. (ment.Ie
Frr.cr 1i 2 3 t -, 1 7 81) 111Ii (1%,-r 11)
2.1 Mar% 3 31 F 7 t, 3 31 2 1) 31 21 1
141tIccurK 2 1 2 8 2 (1 , 2-
Fromn Table' I. it il ie 1w en' that for 2 I-biucir in,)% vm~ent-. ."ito ltericoct cif tle f, reca-t -1w-eel we're -) mile- per
hoi ur ocr l'c in e'rro r. an id 77,7 pec,'ent were 1) ile'. per how oiir l e -, in erroer. lee)r l1t- Iceeecr ccc c'iment -. be2
imwrcei' viere 5c iles jor houir icr lei.- in e'rroer, and K.c jce're't virre Ii ll o- lm~ lcceir ocr le'- in errocr. It A~il[
lo noctced that the fervciat 1 ierikl are -orne~Iat mocire accinrate for the limucr ;w-riodc thcan feer the 2 I-hcccr
lieriodi. ii cant iecrhiaj- lie aiiccunted for hi% erratic arcelcraticcc- v ii are- i'ffe'etjie iltirine, the 2 1-Iiceer
lceric ee. butd %ic h tend it)c avera ge oit o v er the Wc 8-ho ur jicii.
''muId 5. Friminicy diptriceatin cif immcitiien rror c.
101-200 13 I
201- 3W
3111 --UM) 1
401 -5(X) cI
S01 -4100
( he'r 6W0 2, i
Aeag Erroir 2605 M i e 140) % OCR
F~romn Talei' it c-an lit -cen that fc-2 1-liur 1weriodil. 35 otiat of Il8 fac'.ir 7'3 1 ~cent Aere au'cucrat
% it hi 10) miles-. and that thle ave'rage liosituccn errocr for th lW ca-u'- i a - '26-- mil,-. 'I'hi- mc'am- that in
a neajorv c f cf a!-is. the fi rtwea~t jH cp.itic n lies~ %it lin th e in nenu e cli -eel i-eelcar, leor the 18.hc ur h4'rio~.
31 I eit ofi 10c ca-!-. or 0c7 pecent aure' %it hin 0111 mIci I.'. Thei'c rr'la tieicci cc efiiet foer 18 .hcur -j cetib tci ng
inoet-'iceident data was 0.63.
1.1.~M V1't Iil I 'it N G
'Ilit- idrti f miettrilogicaI lilt ramttire conierninmg tilt- relation of iijiper ,air cormteiir andlmoleri it
termm Itt tlit mmit~timemt oif iarfaie cilil frmni' indiicates less interest iam fiirvca~ting lilt- 1pijiii id ofelid frntm,
.Ste') 'I Im %~ ,riott- pitt jalled frttikial rt-feretitt poitu.) oil the -iirfa-e front were
st-lectedtl. uiall% tlijthu i ittl~stiit lilt iiti itt un -Jf the cttitirs~ %,itl t surface front.
Stepi 1711'r. Thei 7410t111ii1 ge-trlIiicu ~ut~tt norial ito the frontt over tile frontal
referciare potjit. %ve itt a ii rvoI.
Siep Votir. The titertinai gratlirmt roiil~ienl. aleong thec trout ierv ne'asured at tie
fronutal refe'renimiit bHiI %' juro-eteetit eirtliva- al-tag the frotiiit te a p'oi-it 2'0 (-colder
than the refertuate potint aiiti .ctlIhi%t-I :ding thet froW t itt a w)MI 2' C rint r. Thedtllance iteeit~e tit-~ Vt w jIm-lts %% .~ i, re intasuear in statttle iniie. and will be
re~ferredt Ieo a thet tttrtinai delafit.eit A hen the thttrttial titatie %a 151inilesotr greater.
or %hieni ctidtr .air X%a- tiiciolittrtti eiwti!,v I tof tit fronital rtiferritce jteint. the thermaldis.tanee Iteri %Aa- aitin.a lkai i-i!l a lo.11111 t1f i.-Mt jniic-.
TIhe .1114 oe pim-wtolirt o titintes thie basitci ra ole ter- Ic i nt ped. ant I the metho, h% (14b which they wereithtaintI4. lThe attempijt I,, iiirreiaet the gtt)strttIiic atid thtrinal ltaratiieter. thrtiugh the nit-diani of the
scat ter eliagrain protlucti v~ceiltnt restilt for all ta4 in w hich thle gett-trtijci parameter was 50 knots4
Tb is fart niecessit ated ii reir ot. t Ihi I r dat a icIi, iled i tc thle eli-roe er% t hatsust ai nedl movement eof
a suirface coild frown ti~er at 30-hoour jitricel i 1i, i v- 4.f 111 utile, per hotutr %a- at tnictettredgival otylt. In
addtitioni it %~as nottedi tihat striia _-radlivnts at the 7Tii41-nhh, le-%tl usuiaii. proucie forecasting errors even
%~hen the geti-trttptii ttiltiiit i tirntal it, thte fronmt i- It-,.- tihani .50 kc-I. Thei getstriphice flow at 700.
iiil nia,% be. sepjaratied into tttiiii-tiipmr iwrtttal it) ainid parallel to, the turface front. It was asstumed that
large get etrtcihic compontttenits puiull I,, ilt surface' fri itt acted as- a tietterrent it, froental nmovement due tothe tenitenci% for Inintir %att i'-t, ft rit. i ir I i"-e re'asonsi. ltht getustrt ict flow noirmal to a front could
not liet- eel at a parainettr A~ithiit t inoifitiatuimi.
Hor"88ani9) rtemrt-ett --rapiitl -I itliti. tiir tieterniiniiig th -re jtit ai frontal reference point
aloing a line normual teo the frin' te~iiire At i ai*- a tifiiedi gee itn ijohit' roeioetutnt which is uasetd as the
ab-ti--a in Fig. 81), wii'i in tirtti. ai~te thet -pitcid of tivu fniuittal refe'rtence 1voinut. Iin an itfrt to) improve the
3. The c'orrelatien utflucient bewoern t thl t osreti antd forecast spe't'tI (uising F'ig. 89) eof frontal
reference potints for the inelcimtentt data is .8(c.
I. The average errotr in liii fitnteat spceeds for the indetpwtednt data is 3.7 miles per hour.
5. The niaxiintau e'rror if tihe iinieeoti t theta is 12 iiles pecr houtr.
6. A freqeoi-Nt (listtribu iint (of erroirs in average speed for 30-.itttr jie'ritd for 3 mph increments is
listed below for tilt indeenden't oiata.
000
1-001
OOO- cy
129
0C
4to i
10) C
'00/
onU
1 .000, 100'
'000,
10,00,
Af) .000.
ccI. !
45 40 35 30 25 __20 15
X0 - 0
z0~
00
0
0
0 $0 20 30 40 so 60 70 so 90 100TOTAL GEOSTROPHIC GRAID$ENT (IN K(NOTS)
Fig. HR. A ioolilir. I gr. ,tr,hic comp. m.neng Inormal to,* t fir -urfave from t at-,$ IN) ru. I1 r I 1i ieg.-tt il~ m.fii. iral t.o the frontal refrence po~int at 7$ NI nil) in It i-k not .icrements. rueli sha is thr t1, al g..tr ii grai .it .,oer tilefrontal refero-no-o ltoint in l$.Ln(,t incemo-nig. C:amr the value ..hbtained froim the graph Ito F ig. 84).
'l'al 6. Frr-.Inency distrhitioon of rrrs.r
30) hfrp. No). (:a..1 Percent
0-2 I
3-5 It8 33 4)
6-8f It lb )
9-11 3 5. 6
12-14 1 I 8
An example of the provedurei, is giveni taping Fig. 90 o.n which the nec$'caro, data art- listed.
Step One. %leasiire gralia'nts at E'a$h 4f firee frontal reference jrnints A. It. C.
Thiere %ill lote i to ii-,'ii. N Ir firwrnt"I -i. 1 ',, -ir wourthI tol Owli hit iliuertecl *tirfaiioe i-odijr andi fccr a..iiiitll Tit 1 iii1.h 1.1 i ' t-, 11-rii titi apijreimickh 14 luiir- aet .1 ci-li'toio .elivad ef lt- 4origittaI
(j. Fl ~t ibili t ,rie ii i 1ii4i ler di ,- 4e ile'l#- q 14i0, N14tcl1ilifl= flii-iialls, 4-iIIIII4 tee. tt',.ful
treatedi u ili thii- -- t''i ltil Ilse liidjfotl 1nertuvei oif tile (retc lia- moliso-el eaA o 111, 9501 V mtei ia..
A s-amnjle ueirk,.iet i. jproti~l fr pr.oc'tical apiv.alifmi (of ti it-.lcniq1 ue tells 1P.13-t
The ..ec',ne I ' tu"-ftecle freuti i- c'alled l lie- C.r.'at Ha~ti- u h.fet t. ie-t friotit. are oriecntedt nsarlycanet hest ant ichir tcee ~ittlI-annorfl t lic e ll ilIe.d -lt ' - I lii life- fuelhii it1 ie. joe'l for the firnt
of I-, 1w one. Thieir mm.11iiiur irlojrecgrr,,o ill th le 4,rat I'laiei- atid Tevit- arrea. i~k elate- iriuncipallit toi live "hNiig.
ing action- of thew tcld air t itihitch tech% oirtir tile lftccL% Nllmtlaiii ia- it virtlle-~ arou~tnd the istuisern
extremitii of a hligh lo~re'~ure Jlrt--i t thle wotrtds. litl t1he llah -i tiic~ -itloliepit tel INi, issp. a cie-heent is
I4K-ratefd t-t eof tile- tilit mIIleridian mide i lit' cd 1l ftgia vcitt ict tic' vlttrll %at.e. a- it e'roe~- ,. ithe WWI mridian.
The seurfae trmelli ill INi area %ill il-eialli IN' itiivtrte'l htisil cst It, oviles floglhI llrtiugh l tw troutgh and eaiterliswinds~ north oif the frontt. Nformhlll ilt 11th moemilt oif the poertiocn of tist- frtou eti-t fclife qth meridian
May be comifhtedt thlrtelii the met' tthd- om-i'e flor frocntsi ci tc Iogs (itl'.
W'ORK $H1 A~~;' F01 CBI~&ATEORY I COLD.1 FBON'r
I)ATI:
REQUIRFMENTrs:
1. Fronrt tor pirtion tof frttet tender cin-ide-ratifon moist loe torentrd north .of70 degreeso. 1A edging actioin to the windwtard .f(a niountain learneor .. ooseldnot h~e a factior in the fronrtal moverneit.
2. Doi tot app1 ,k this techeniqlue et surface ceold friont% that lia%... forred in estrouigh too ther lee iof thar Rticky lou~tntain,. until tiar major loeteo ee tJ ia fronthas pastora eapt of' the 95th meridian.
DEVIKlOPMENT:
I. Ikcbc surface caold frnti on time 71N(.ndls clhart.
2'. So-lee't freental reference potints oan ther friont psreferaly isetween the cointour.fronrt intersetins. No~te the latitude okf earls fr-kntal reference joint
3. Mocesure the to~tal geropihic w~indl at 7M~ mi. sover each frontal referencepatint
4. Merasure the geoootophic cobemonent normal tee the* frnt at, determinmed It,#the cpototur front inteorsectioins
S. Fanter F'ig. 881 with the values obtlainerd from opearatioins 3 andi 1. Thi.. is thevalue of' the mestlifiesl coenpemeic notrmal to, the frnt
6. Froms each fronatal reference 1sbont lor-s-ed~s along tive fr..nt 2' C vtoward coldeirair to the norrthepast ansI 2' itmuardls warmer air It) the sosathuest. Measurethe distance between the twos tempserature lesints in statute miles to ohetainthe thermal distance term, If tiae thermal slistanc so 15011) miles owe greatertor if colder air is encesountereei wthens gwss'eeling t.. liar seeeatimwe..t o)f a frqenualreference pomnt. assign ISMN moilest tu ther thermal distance term
7.With the values taltainedl from opeorations, S ansI 6. easter Fig. ite) for a inalfowrast epe. Ins statute mile. hser ieuer for 3iluo .es.ar
fl. M1lle each freosstal reference jsoint withs the -pelee indiecatedi from Fig. it' fewr301 henwrt aloing a line normal lt the froint threegis the fnrntal reference povint.
9. Connerct all preroreted firvemtal reference po"ints. Ctoflue1t the northrnosotrfernce patint it the peredictedl lno center poseitisen. The line consterue led isthe .30.heeusar prionosticr coold froont pesspitesen.
MODIFICATIONS:
1. Ifthe surface frnt lies well too the vaest asf the poriniral trough at 7410 smbs andist under nothswest lo asg 74M( ml. froenteelyipi is likely. %Isuve the frntwith 75 prcenat af the speed indlicateed fromis Figl. 84.
2. Ifthe portinoe tme srface front esentreelled byt an inverted surfae trougth.eapt to west LV lowtrougih the tresugh indicatede 4u the surface iseebars. is greaterthan the poirtiepan to( the fronti copetrsllee It% a nowrmal trouigh. meeve thse fireent at50 percent idf the speed indicated (reom Fig. 1WO.
A. Threo will leer a elencvr five fromteeslyvsisnerth tof the last invertedsurface, iseulsar. with a wiluall line or inelseceil triough formsing insarostimately 18 haesos at a Isseation fiscal lay thse (mull -pensi o( theoriginal ftrental enoputatitn freon Fig. 8t'.
3. In thve event that a necar rolearwe fronet orzists thriough the msietldlewetrnpoortion sof the United Stairp under west "o at 7(111 ambd. the surface frntsoul be projected until it beo~esr parallel tn ow he. eisig owat 7W11ms
At this point further projress %ill pesraill cese.
13.1
In ft#e w- %edge-front with the 10th~I meridian will he referredto Vf I i, f ill give the 54,uthl4arli di.,placerlIent of the front for
ill~~ )A~ ida, anti Vera Cru~z. Mlexico. T'his line- %as chosenIll~ \.I dU "b. ni( Mexican cts~. and to avoid lte maountainous
iIf Ijtr. w I,, v'.lain the mechanics of wedging action in the GreatPlail- Ir, ll. ,~ HItK 4'. .:i n ,litions oIf the upplier air to) subseque-nt frontal dis.
I . V-1th I-IN fihi:Ii- nhl. ir I IlI' , hvight contours over lte uedging surface (cold front),
2. Smit ii I'. ii at mb hl. I1- idit if- tel % I li height contours. indicates slow niovenent of the
:3. '1 be .ljr4tjr i. d1 t... A t 8..f fill, I-im~ich ,iro, clo-ely related tol the frontal movement that] thestrcrn-th id Off tlie .o
1. (oldf aiheti.in at 700t ridl t-, rHa ri'rthll~-t of tife- fri~l reference litiint intensifie-4 the wedgingactio~n. %~ arm as ,iti itn iiri t lie -am ir,. dra.i-.toirages thve wedging action.
Four ba~ic filow Illtrn at 9h.01 rb -hli-iin ini 91- ~ through 904 indicate the nature of subsequentdi-,placenieiat of the -oirfaee F.L-r 'i. iglirt Ill indticates long term northerl% flow over the %~edgingarea, a conditio.n fa isralilv f-.r rapid fi.I iict iire 912 inldicates long termh m)utherl% ffi which %,ill
discourage- moaliiardl lr..grr. off the fr,.nt. Figufre 9)3 indicates that a change in flow over the wedgingarea is likely frorui ntsrtlierl to -ouolherlY indicating dleceleratio~n during the latter portion of thve flirecaitperilod. Fiugure- 91 indivatE-, a c~hange- front iti St herli to northerly, and that acceleration %~ill take- placeduring the latter piortioin of the forecast period. For the. purpose of illustration, the basic Rlow patterns areezamples of classical ridge andi trough niode-.; however, numerous unusual contour configurations are oftenobserved. This fact proihibited Edirect use Eof wavelength andl amplitude as parameters and madle it lees-
sary tl (levis- a nmethod (shown in Fig. (15) for mieasuiring lte Edirectionf of flow to the north and we-it of thlefrontal reference po.int. The method is basedl Ein measurements made at 8.50 mb. Point A is the frontalreference point. Point 11 is located 500 miles 111W north of Point A and will usually lie in the coldI air. PointC is obtained by following the contour over H111M mile's upstream. The difference in latitude from A to Cis a measure Elf tile direct ion Elf flow o~ver the wedging surface. This differenice will be referred to as .1o.-Point D) is located 1000) miles west lof Point A*. Point F is taken 1000 miles upstream from D) or at lteintersection of the hright line with the 125h meridian, whichever occurs first. The difference in latitudebetween E and D) indlic4ten the western extent of thve flow~ 1-C or the change in flow that existls to the West.
The latitude difference E-I) will be referred to as .1 os. The A 0 values are considered positive if northerlyflow is indicated and negative when southierly flow is; inudicated. If points 81 and D) fall in an area of flatgradients, a 0,. will then he latitude difference li-A avid A 011 will he zero.
As previously mentioned, thle advection factor at 700 sub northwest of the frontal reference point mate.rially affects the subsequent displacement of the wedge-front. A simple method devised for evaluating theadveetion factor at 700 mb is shoi a in Fig. 96 and described below. From the frontal reference point. pr--ceed 250 miles northwest to locate point II. Follow thle contour over 11500 miles upstream to locate point C.
13o
Of U
biI
ILI
TL
It.
137
- A
E
138
I5
U
I
I
U
IS.11CS.1I,U
.5U
Ii-I;
/
'7139
N \
0 I'4 1I
U
IU
*1I
t
*1
-- ~~C~ -
~ -~ V:
1101
00q
000.
141
LnA
0I
coj
391
142
I to10 0 00 100 100 400 S00
SAUrtMii
Fi.9.A ralygabt~bantuspe fmwmuto h ratMi eP futwo coe o easa 5 iwie f he95hnisiia. ndwthn 46 mle f hufrntl d me - Te eaylie huldheepslmmud20 h
16g iajda, ih h v a drctyorssh ina rlecepin. Les. Nlo eueeasIO i ws 0 he9t
meidan ad itin140 mls. h una ewaspit h ealno h 5m i e~s~ai,5 h rna
reisis. aitdemeins h frsas see f owmet o te ndee~vde rot)I.mle ps on h S eOleim
In.0 momeigDeai.llet aoa0n ~e 'na ae 1mta 10000, spesnesanse mi~
spaud ~ ~ ~ ~ ~ 1 0000 mat 1etruu huamtela m raAa iiessad
143
Note the temperature difference between points 11 and C. Ave-rage tihe observed %inds between the pointsto the nearest 5 knots. A simple multiplication a T(B.c) X Vtm ) is the advection factor at 700 mb, de-noted A '0, and is considered positive when indicating cold advection and negative when iddicating warm
advection.
At times, the presence west of the 95th meridian of a definite closed low center at 850 mb within 1400
miles of the frontal reference point prohibits a representative computation of A O. and . Ow. Therefore,
all these situations where such lows had at least one closed 200.foxot contour and were verified by observedwinds, were deleted from the data sample. A separate investigation of these cases indicated a strong rela.
tionship between the location of the 850-mb low center relative to the frontal reference point and subsequent
frontal movement. A tissue overlay graph with a vertical line representing the 100th meridian and a cross
bar for the frontal reference point was devised and utilized in this study. The overlay was placed on the850-mb charts and all low centers west of the 95th meridian and within 1400 miles of the frontal reference
point were located on the overlay. The subsequent 30-hour average speed of the front was plotted. Speed
lines shown in Fig. 97, were drawn for these values, and this graph was used in forecasting. In the event
that more than one low is pres.nt in the area covered by time overlay, all centers should be plotted and the
final speed forecast is taken as the arithmetical average of their speeds. This method is referred to as the
"closed low" method. Statistics for this method are as follows:
1. Fifty-nine cases, from January 1950 through March 1952, are included in the total data sample.
2. Thirty cases, front November 1951 through March 1952. comprise the independent data.
3. The correlation coefficient between observed and forecast speeds based on Fig. 97 is .85 for the in-
dependent data.
4. The average error for the independent data is 4.4 miles per hour.
S. The maximum error is I I miles per hour.
6. The frequency distribution of errors in the 30-hour average speed forecast is given in Table 7.
Table 7.
Errw in 30 fir No. Cases Percent
0-2 10 33.33--5 In 33.36-8 6 20.0
9-1I 4 13.312 0 0.0
When there is no clowd low at 850 rb, the "open trough" forecasting method is used for the wedge.front. The parameters a ON and A #w are utilixed in a preliminary graph shown in Fig. 98. The valuegiven by this graph and the advection factor (AF;0o) are used in Fig. 99 to give the final speed of the cold front.
The flkning statistics are presented for "open trough" eases:
I. The total data sample comprising 60 cas, covers the period November 1949 through March 1952.
_ 3
144
4
-4-
16 -12 -8 -4 0 4 2 1. 20 24
Fig.98. Prehiumiary prrdiia I Great Ma~im wedge brouts (op... trough category). The ordinate Ar#Niipkloted an 4'inrc.isets. The aheisma &w meplttcdAn finjm Ats. Carry Ihe value obtained from thie figure to Fig. 99.
2. The independent data, comprising 28 cases, covers the period November 1951 through March 1952.
3. The correlation coefficient between observed and forecast movements based on Flogs. 99 for theindependent data is .
4. Th average error fro -Fig. 99is2.66 miles per hoor.
S. The maim n error band on Fig. 9as 17 aniles per bour.
6 The fiequency dstribution of erors in the 30-har average speed forecast for 3 miles per hour incre.
meats is sted for independent data in Table L
30 HUr Case. Pereet
0-2 21 75.2
54 4 14.20-a I 1.59-11 0 0.0
12 2 7.1
145
35
307
03
2-
-10 -50 0 50 00 I50 200 250 300 350 400AL 700
Fig. 99. The final forecast speed (open trough 850.rb eatelgory) of the Great Pisins wedge frost in statute miles per how alonga lime connectintg Bisuarck. North Dakota. and Vera Crus. Mesaco. Thle ordinate preliminary predietiom I as obtained fromsFig. 96. The absciaaa ia the advectian factor at 700 mob. The fanily ofcurves indicates the Ainal speed fureaLt
A casual inspection of Fig. 99 reveals four large errors. The errata occurred when a wel defined ridgewaa just west of the frontal reference point and a trough wa, near the west coast of the United States. Thesesituations fit the basic decelerating pattern shown in Fig. 93. On three of the occasion (indicated by thecircled numbers ;n Fig. 99), the ridge remained stationary resulting in northerly flow over the wedlginlg areafor the entire 30-hour period. Two of these cases were associated with warm air advection in advance ofthe ridge which suggested that slow or stationary ridge movement might occur; however, other ridges ofsimilar character moved eastward in the normal way. Since attempt. to insert parameters that would
* ~reflect the movement of the ridge were uncesaful, occasional large scale errors will result when an unusualridge or trough displacement occurs. The fourth large error (indicated by the asterisk in Filg. 99), was theresult of an unusually large deceleration pattern associated with the development of an intene low in New
* Mexico during the latter portion of the 30-hour forecast period. The wedge-front moved sou,.hward atthe rate of 16 miles per hour for the first 18 hours, then as the New Mexico low developed and moved intonorth Texas it moved northward as a warm front back to its original position.
146
Work S. I_ -k fta te ?sn.dotgg 147. The third t9ys Go% -_t
is often observed durinig the 44,ra*h' ort~v .Teewdge formations a esii fa eori6ion ofthe so'u'thrn isobar" tf a coM' antici clone which moves elowly eastward north of Is, .3. Th --
easterly component of the wind t~kath of the high center carries the rcl44 air directly, into the-Appa se anOMountain barrier which deflectii'the air to the south and retults in x northaeast..outhwest orientation of thesurface isobars. This s% noptic dlevelop~ment usually occurs &(ter all frontal systems preceding *the anti.cyclone have been forced into the Atlantic (these fronts belong o.type one). However on occasion the wedgeformation is directly preceded by an east -west cold front and sOuthwitrd progress of this wedge-front wil
be discussed in this section.
147
WORK SHEET FOR GRFAT PLAINS WEI)GE.FRJONT (IE.N TROV0Gi CATEGORY
DATE:..................................
TIME OF &S0. AND 700-mb CHARTS:....... ................................
REQUIREMENTS:
1. The surface cold front should lie apporoaching an easit-wesat oirientation as it crosses the M00th meridan.
2. The surface isobars north of the front should display an easterly component.
DEVELOPMENT:
1. Notc the latitude where the surface front crosses the 100th meridian. Mark this point on the 850.and 700-mb charts.
2. On the 14S4).ml, chart lahed the frontal reference point A anti proceed SOOt miles north of the frontal reference point tolocae pintIt.Fol~os thme contour liver loint H 1414) mniles upstream to locate point C. The latitude difference from
point A too C2 vill for referredl too as4 -%#. It shall hie considered positive when point C is north of point A and will beetwosidterrel ene-atise-wh lin ptoint C it, located sobuth tof point A. In the event point BHis located ina completely flat are
.4.sIvo-1 dlatledifferenCe1 H to A...............
3. From-i t he from tal reference povint proceed I (N) m iles west to locate point D. Follow the contour over point D 1000 miles11pbtram ior lt the point wshere it crwsses thme 125th meridian whichever occurs first. The latitude difference E to D%ill Ite referred to as 4% It shall Ibe considered postitive when E2 is located north of D and negative when E islocated south oif D). In the event that po0int D) is located in a completely flat ares AOW will he zero.
4. Ye ith the s slics from two and three enter Fig. 9)4 foor a prellimvinarv prediction value. -........................... ....... .....
5. At time 74)-mi. level lbriori-ra 250W miles frome the frontal refere-nce point to thot northwest to locate point B. Follow thei'oitor oe'rIt ,4) mle.. ul..rrm t loate;wwt .ae give tempeoravoiredifference from iito C. This lvaluiewill
Ior referred to o a4 T(it - c. It will fore on-i-lereimc ;ihtive wthen tile temperature at C is colder than at B..4se-rago, thle vifiwrved winds fromi 11 s4v 4: tot thve nearest 5 knotso. Thio will lie referred to as V(B . c)......... .Mlultipely Ttis -- C) 10) V~t . C.) to oltain the atilvection factior at 74)(1 mlt Aj' ,oo ..
6. 4. itim tile values Obtained from operatione. 4 anti Wricter Fig. 99 f#or a final peed prediction in statute miles Per hour.
7. liove thme sourface wo-dge-frownt ailong a line connecting Hismarek. Novrth Daskota. and Vera Ccizs, Mexico, for 30 hour*at the speed indicated from Fig. 99.
WORK SIIEET FOR GRIEAT PLAINS %EIGE-FRONT CLOSED LOU CATEGORY
DATE: .......................... ....
TIME OF 850-mb CllAHT: ..............................
REQUIREMENTS:
I . The surface front should ho approaching est-weAt as it crmroe the 00th meridian.
2. The surface isubas n"t of thme front slce,:ild display an easterly component.
&. A closed low must he present t tlniwetof the 95th meridian and within 1400 miles of the point where the surfacefront crosses the 100th Meridian. This its tive fronrtal reference point. The low should hae at least one closed 200.foot contour withs the observed winds verifying the cloed sutie
DEVELOPMENT:
1. Mark the frouitall reference point os the baoe map. Place Fig. 97 over the base map with the cross bar over the frontalreference point, and the heavy vertical line directly over the 100th meridian. Mark the position of the geometricalcenter of theclosed low on Fig. 97. The powition tof thfi renter of t he eltosed! low indicates thme average 30-hour speedin statute Mile per hour ................... ...... - in the event that More than one closed center exists in the areacovered by Fig. 97, note the, position of each center. The final speed forecast will he the arithmetical average of thespeeds indicated for each low center............................
2. More ithe wedge-front for 30 hours along a line connecting Bismarck. North Dakota. with Vera Cruz, Mexiro.
+200 0 5 i0 Is 20 25 30 35 40
+100
0
30 0 -10 - _100_20
iw/I
-c-300 -200 -100 0 .10O0 . 200
&Z WEST 630
F1. 100.- Preliminary prediction I cast coast wedge fronts. The ordinate A7 cast is the height difference. ec'rrected fir lati.tlde. at U 8 mli(Wn the frontal reference point to a point 60 mileo cav1. The alirisia A/ write ii the beight difference, row-rected for latitude, from the frontal referenee point to a point 600 miles west. The AZ values are plotted in increments of 100 ft.Carry the value obtained from the family of Curves of graph to Fig. lOI.
The leading edge of the wedge is usually characterized by a nose of cold air directed towards the south.west as it advances down the coastal plain. A line connecting Caribou, Maine, and Cross City, Florida,will normally bisect the nose and be approximately the axii of the wedge formation; therefore the displace.ment of the wedge-front can best be measured along this line. The measurements of the parameters willbe made relative to the intersection of the wedge-front with this line, which will be called the frontal refer.ence point. The speed of displacement obtained from the graphs in this section is the average speed fora 30-hour period. Frequent short term accelerations make use of the graph speeds questionable for periodsof less than 18-24 hours. Since the existence of a wedge-front in the coastal plain is rare, only a limitedamount of data was available for this study. Therefore, the solutions are tentative until it will be possibleto test them with independent data. The following observations are the result of a subjective study ofupper air cbarts relative to the submequent .30-hour displacement of (he surface wedgeafront.
149
40 ___5 10 15__ 20 25__ MPH_______
2 :is
35 14_ ___
4
0
I.J
'L 3 3
5 7 1 1 s 1s;9 2 3 2
AT65Fig 10 . T wfm frca1- ( o catcatWd e not inSail mie orhxrfo 30h usaln alie m n tn
11ewliaro the__ _______ar _______ i~ from__ Fi._ 00_____i#aA r
Fi. l At Trre t-m fnrrc e. 1--do et cat 85wedg th olha fte frontti tbeunsprh a l re0fersnc alont lis conductine
th ~u1 rItlrgeIf~rii. s in *lrd . nti e mftesurface4N miesgfro ntalrfrn.pittoadtenrhat
2. A %vtak tentlotrat urt, gradeient at 850 mb to the northeast of the fronta reeene otwe is coniv#t lare 1)smttuall ili.lard duispnacoft.sraewdefot
3. Northi'rli 114)w iit 8511 ml, over the leading edg of the wedge is conducive to large southward dis.plavernent fof th 1w.urfie poedge-front.
4. Sotitherli flip% a, 850 nib over the leading edge of the wedge is conducive to sai southward die-placement of the surface wedge-firont.
The transfer of these subjective observations into objective parameters was accomplished in the fo.* lowing manner:
..................
ISO
1. The temperature gradient at 850 nib was measured from the frontal reference point 600 miles to-ward the northeast along a line connecting Ca:ibou. Maine, and Cross City, Florida. The valueobtained from this operation will be referred to as AT.w
2. The height difference 600 miles wes dl 600 miles east of the frontal reference point at 850 mb wasmeasured and corrected for the latitude. The values obtained from this operation will be referredto as AZ west sV and AZ east % and will be considered positive when the height increases as wemove away from the frontal refereipce point snd negative when there is a 6ecrease in height awayfrom the frontal reference point.
The AZ values are utilized in a preliminary forecasting graph shown in Fig. 100. The result obtainedfrom Fig. 100 is plotted as the ordinate and AT & as the abscissa in Fig. 101. This graph gives the forecastspeed (in miles per hour) of the frontal reference point for 30 hours along the line connecting Caribou, Maine,and Cros City, Florida. The following statistics are given for these cases:
1. Thirty wedge-front situations comprise the total dias sample for the period November 1949 throughMarch 1951.
2. There were insufficient data for a representative independent check.
3. The correlation coefficient between observed speeds and forecast speeds based on Fig. 101 is .88for the dependent data.
4. The average error is 2.2 miles per hour.
5. The maximum error is 8 miles per hour.
6. The frequency distribution of errors in the 30-hour average speed for 3 miles per hour incrementsis given below for the dependent data.
Table 9.
Emri mph30 Hr. No. Caae. Percent
0-2 18 603-5 10 33.36-8 2 6.7
Catalog of cases for all categories of surface fronts appears in Appendix VIi. The dependent datasamples for Category I cold fronts and Great Plains wedge-fronts have been omitted due to the large volumeof the sample. The entire data sample for the east coast wedge-front is included.
On the following page is presented a sample worksheet.
151
WORK SHEET FOR THlE EAST COAST WEDGE-FRONT
DATE:..........................................
TIME 850-mb CHART:...................................
REQUI REM ENTS:1. Front must be approaching cast-writt a% it crosse a line connecting Caribou. Maine. with Cross City. Florida.
2. Surface isobars north of front should display an easterly component.
DEVELOPMENT:
1. Construct a line on the 850mb chart contnecting Caribou. Main.. and Cross City. Florida.2. Note the latitude of the point where the surface front crosaes the Carihou.Cross City line. This isthe frontal reference
point.3. Measure the difference in height between the frontal reference point and a point 600 statute miles to the west and
correct this value for latitude. The corrected value is &Z West ....... r..... ......... .(If the height increases tothe west. the , alue is positive, If the height decreases to the west. the value is negative.)
4. Measure the difference in height between the frontal mefernc point and a point 600 miles to the east. Correct tivalue for latitude. The corrected value is AIZ east . ......... .. .......... (If the height increases to the east, thevalue is positive. If the height decreases to the eat. the value is negative.)
S. Measure the difference in temperature in degrees Centigrade from the frontal reference point to a point 600 miles tothe northeast along the line connecting Caribou and Cross City. This value Is ATaso......................
6. With the values from operations 3 and 4 enter Fig. 100 for a preliminary prediction value.
7. With the value from Fig. 100 and !. s1raso obtained from operation S enter Fig. 101 for a final speed forecast instatute miles per hour.
8. Move the frontal reference point with the speed indicated from Fig. 101 for 30 hours alonmg the line connecting Caribouand Cross City.
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169
APPENDIX 11. Ta"l 1. CAkpr7 I eydm - adogl (Cendmid)
Gam No. Yewr Data Mesib Tim (EST) NRm 3.1mg Odomi ofVONa CYdem
46) 11 Dee low- is47 (Viehity RAP) 12 Doe 2200 30 CG48 (Voimy XD) 12 Doe 2m6 N GA49) 17 Doe 3w0 36 CASO) is Due 1060 24 CA
SO) 20 Dee 2200 N CAS2) 21 De 10rn N CASP) 2 Doe 2200 N4 GA54) 25 Doe 1000 N GA55 27 Dee 2m0 24 CG
56) 1951 2s )as 1060 NCA57) 2S Jam 2200 4C A50 2 rob 2260 N GA59) 7 Feb 2260 30 GA60) 8 Fab 1000 is CA
61 is Fab 1low 48 GA62) 21 ma, 2260 N II63) 22 Mwr low N %f
14bbqc,.isa tio to., modesfo of ame: G GA - tI. 5 i nsa wmeb bum GoM of Mlmaa 4 vslm& N - &oeem is N-9 S e m~omdoalub from Arelic Circi M - evelaem s ins iota"; CG - mood pine .,h8m 1moe suonod bw wm uas4 wow~ he.
1 70
AlN3I It T1. 2. 4tW a*4 I cycilu - devdopeent
IMewt as)d# flow llcxis Mure Filling"lm...g A r ais, Ie wh m lA tud c Stage I Stagr " Acta Iianm caat
C astat TerM I cia tws
(a) (b)(r (d) )( (9) (h) (i) (0)
I 0 -5 31 28 S.4 2.7 36 48
2 -(k) 30 3 - 2.9 N -
3 8 28 (303)( 2.1 2.3 Is Is
4 7 -2 3S 27 3. 34 24 36
S 9 1 3?. 14 36 3.2 18 36
6 - (3) 2 27 - 2.1 N -
7 13 ) 40 32 S.3 3.3 N N
8 5 1 38 :2 0.7 4.2 Is 30
9 Is (0) 35 28 S 2 3.2 N N
t0 4 -2 i1 29 1.2 2.7 12 18
II - 1 38 26 - 4.2 I8
13 13 a 45 24 5.3 > S N N
14 - (-3) .- -. - - -
Is 13 38 14 5.3 42 N N
16 11 -4 (40) 21 7.0 S.0 N N
17 7 -7 2S 3O 5.4 2.2 48 36
is 9 -( 411) (35) 4.7 3.0 36 42
19 9 0 20 It 4.0 O.S 6 12
20 a 0 25 :5 3.0 2.1 30 18
21 6 -2 25 Is 2.2 2.1 12 12
22 6 3 23 20 0.8 1.7 is 6
23 6 -3 31 24 3.0 30 Is 30
24 4 -7 38 2l 4.2 3.8 N N
25 I0 -3 32 (3s5) 6.0 2.4 N N
26 30 -3 32 19 6.0 3.3 N N
27 0 -4 28 19 S.7 2.7 36 N
1111 -1 3o 1* S.0 3.0 N 48
29 8 -6 17 7 58 0.0 Is I8
jo 9 0 32 19 4.0 3.3 24 42
31 7 0 )ver 5 (30) 2.1 4.2 30 36
3 3 9 24 7 2.S 1.0 12 12
33 6 (-4) 3 17 3.7 3.0 42 36
34 7 -6 23 o S.0 1.1 18
a S -6 30 14 4.2 4.2 N N
3i is -2 45 (301 4.2 4.6 36 N
37 14 -2 46 I S.S 4.8 N N30 Is -4 3S to S.8 4.7 N N29 6 -7 33 is 4.7 3.S N N4 5 -2 47 L9 . >5.9 N N
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171
APPENDIX II. Table 2 Category I cyclone - development (Concluded)
Case No. Instability Ad h al A lu Sa 1 S 2 Hours Before FillingContrst Term Wavelength Actual Foreeast
(a) Sw. Appendis II Table I fi date " e.a*.(b) C eae.etsoa kme puepeOdteu to 401a.1-1rb flea .Ove le m..(r) Wasiume Instabilitp liden mimsm Mimi.I Iessdhibly lodes. The masimmI. i aiwaye sawarle a. air from the minimum.(d) 'remperom at p.4le 34 houre trevd et sauropbe speed up4ateaee mine tem netnsr at low oeer. at S0 ob.(1) measted in deoee bt&mOIde so ?00 Ob atm ti pers"e aein the low eaw kermn the ridge mme weN at the low to the trough lio eaSt.(f) MasimuIm htioude diluearme of the 70-mb eegaew ovor to lew 60 to rde WONo the elow i teo egb mal.(a) %.. F4g.3.(b) Svee Vg. 2q.0i) N "lIise Noe.UMImg Sptm.(p) spe the Compoite Grap, rg. 41.(A! Not enteed in graph. Deta mimeg. auiemlms ,mefeble.
(rn) Is pIe eae". Some data assmgm. Atimaatoe believed eart.
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176
APPENDIX V. Table i. Category Ill cyclones -- orgina: data sample.
(Data in parentheses estimated, and believed eorrect)
AT 500.MB 1,FVI:L-7(M)-mb, Initen'ity
Lowest Half Wave. ComntCam Date Central )istance Height of Laration H 3av.. CwataNo. Pressure tp-( 4tome Contour of(Closed length I 3 0.lr (las
to NW Flow Over Law Low(a) (b) (C)
201 1947 21 Dee IOO0E 1012 mb 450 - 10 7 NC202 30 De 2200 999 - 183 450 NU 22 16 (29) 1)203 1948 23 Fab 1000 992 -- 178 300 NI 23 18 14 NC204 26 Feb 2200 998 - 183 .10) , 1 14 24 I)205 3 Nov 1000 996 - 181 -- 15 10 16 I)
1206 17 Nov 1000 998 - 183 -- IS 14 22 1)207 26 Nov 2200 1002 575 - 12 14 NC208 1 Dee 1000 994 - 171 17 12 Is NC209 1949 1 Jan 1004) 998 -- 175 500 NW 12 13 16 NC210 10 Feb 2200 994 176 700 W 16 20 21 NC
211 20 Mar 1000 996 - 184 - 16 15 16 NC212 10 Nov I000 998 179 - 22 6 12 D213 9 Dec 2200 994) 178 - (20) 16 24 D214 15 Dec 2200 102 I 900 -- - 14 13 NC215 18 Dec 2200 104)2 a 550 - - - 14 11 NC
216 24 Dec 1000 996 - 177 - 1s 20 16 NC217 1950 7 Jan 2200 1008 > 1200 - - - 12 T FT218 9 Jan 1000 994 - 178 - 1s 16 36 D219 11 Jan 1000 1002 1200 - - - 14 T FT220 14 Jan 1000 994 - 175 650 NW 18 24 24 NC
221 11 Feb 1000 1002 750 - - - 10 10 NCS Mar 2200 990 - 182 - 12 22 33 D
22311 Ma 2200 998 - 183 - 37 20 T FT224 25 Mar 2200 980 - 182 - 22 22 28 D225 I De 1000 996 - 179 - (18) 12 IS NC
2261 De 2200 996 - 184 - 18 11 13 NCn7 S Dee 1000 1006 500 - - - 9 10 NC228 31 Dec 1000 994 - 178 - 13 16 12 NC229 1951 1 Jan 1000 999 - 183 500 WNW 27 10 12 NC80 15 Jan 2200 962 - 171 - 1s 24 17 F
251 29 Jan 1000 1008 950 - - - 19 13 F232 Jan 2200 1004 67S - - - 21 14 F25 1O Feb 2200 1002 > 1200 - - - 14 T FT2U412 Feb 1000 1002 1000 -... 13 T FT23 19 Feb 1000 1006 550 - 400 W - 10 20 D
236 5 Mar 1000 990 - 17S - 24 19 T FT257 9 Mar 1000 1002 1000 - - - 17 9 F2" IS MW MO 964 - 173 - 12 25 20 F3n 1 MW 3W 994 - 18 -1 1 is 17 NC
I t lest upsteausa& to estmar troughb west of eyeless.
It) I. iles bes erde toes Smi low. Okuegh. imillsasd.allges -=--d~ daeswesoa r w st 10 e~ Gm sees alea latktde t esai las smut.
177
AII;ENI X V. TlIDie 2. o,.mntrud gr.u Iy daita fr Callrg.y III cyclmea.
(Data in prItlhroio roolinlslrif. and hkelirvotd c, rrectl)
AT 54Nk)II I ",I. -
N ru (.) ir Central l)i".t.,ie{r llright 4.f I A-AtiII lalf Wave. I,..lPrromiurr 4 *)-mi.l.r I :0mtmt.r 4.f ( I, o- I Ientlh L 30-hr Claoo
it) N F4im 4 ver I ,161 (I) (e
1951 21 INtkk)I 14i)4 mhi. > 121K) O T "rr2.41 21 Nov 2200 Ilk >I21) 23) T rf"242 . 0 W2 13 2 )
"43 ~18 1 lor 22(m) Wk) 1 ) 74 A1 41244 19 1000 990 177 74M) No 20 20 12 F
"-4) 13 Jan 2200 994 180 22 15 24 1)251\ 20 Jan 2200 99 178 16 20 25 1)22 21 Jan 14XX) 996 19 14 19 25 1)253 2 Feb Irtk) 998 183 Is 15 12 NC254) 2 Fel. 2200 992 182 2 0 18 II F
255 . 17 Fei. 224) IN) 7(X1 800 NA - 13 22 D2544 W 18 Feb Itkk) 99) 182 18 17 19 NC257 21 Feb 224k) |I 141 ) - - 8 T FT258 2 Mar I00) 1") 184) 54m) NA 30 I 14 NC259 8 Mar 1I004 liM1 It4) - 640 RNW - 7 14 D
264' 8 %tar 2200 998 184 64l k N W (28) 10 13 NC261j 9 Mar INK) 996 182 54? 1 .% 20 II 23 1)262 II Mar 224M) 91) 178 4KjNl A i 22 1) Nc263 13 Mar 224) 1002 44)) i - 10 '1T 1-["261 17 Mar 220) W9& 18) 3Wk) No 15 14 16 NC
265 19 Mar 22Wk) 101 > 1200 - - 8 T FT266\ 20 Mar IW4O (IO0) 400 54) No%" 12 15 NC267f 2 Mar 2.4k) 999 - 183 50 No 25 13 20 D
(a). (b). r). (d). (e) S4
ame . fso receding table.(1i) Scive puaitmma tol the "me rycrlo at. €e'ms)rcd independent cams. and are eonet.eemed ith nbraket.
170
AqPPEN)I X V I. I)1u. (:,,g.ry I, Cy lck.
L)ae Time ft. Initial Ma. Tmp. 71411) 850 850 M) fr. 30-hr.Doe lie ]A)w ]nten. It.ten. Sha|mrp. H9111 'J'etl,, .Afdk ru. "J' vilp. ing Di r. Speedr
Plityv Niltv ,N A F~~r actor F~actor 7(N;m) e il, r l..
.Aizet an. J. M. and It. Sh.piv) k c id St rat o-I heric Trin~wratutre (Ia,ar-/ 4I'
With l'resstire (ianie J. .11; tI. 191_ 19J../
I'etew. It. G. (1951). ~i lieuimal comuinhuuuic,' .~ a
B1jeikne-s. J. mid J. Il44ln44o , 11- , 1 P. the i heeor% 4~ ( :v imes," J. Meteor. a. U -22.
Charney, J. G. (N-09), "T1he I)1narniiM of Lo~ng Waves in a Ii~tr.'iiv Wrterv (ufren V.':
135-162.4
G;eorge, J. J. (1Q49), "Ott the IRelationthip) Ieti~een the 7t00.Millibar Surface and the Be vio .f Pre-st.rePatterns at the ;rowid," Easterni Air 1.iiie. Nteteutr. Dept.. M unicipial Airpowl. Atla 1. Ga
Palmer, W. C. (1W."( )n Forecasting the i rection ofl Nfnement of1 Winter C.donIIWS. 11",n. Uvae. Url.
9, 181-201.
Petterssen, S. (1940)). It ivithor A.lris and Frw~astineg. 111l. 317.
Rierli, HI. and .Awiates ( 1452), "Fortecasling in Middle L.atitudes.- .Meieor. 3lion. 1..
Wulf, 4). RI. and S. j. OW41 (19B). UT.*Itilizationu I41 the I ntire (uurwe ofl Badiiiwo~d .fight, ini Weather
Diagnosis,~ Mise. D ept. No. 11), 1Iln i%. of Chieag..
No. 1. lsotrojli - and Non-lstr,,pi- I l : , n e ii , .. Ow ' .- ,. "orfave I au'tr, lleinz I.L ttuu, (e)-
phvsic ' Iesearch I)ire t ,riz'. ior. em er I4J(l
No. 2. (Cla*.ailed)
No. 3. Diffriction iEffec',i in the l'r pagatiou oif e r,.ion,,i %aves in the Atmosphere, Norman A.lltil ell, t,eroph;'sical Researc h lirrttr,. :'-)05(.
No. 4. EvalurAlon of R]{ulto of Joint Air lorc - V , kther Iluranu Cloud Seeding 'l'riv!u Conducted During
Win! ir and Spripng 1)49, Charles V. Anderw.,. (,erojhvmical lHessarch Directorate, May 1950.
No. 5. Investigation of Stratosphere %inds and '; -rtures From Acoustical Propagation Studies,
Albert P. C(.ry, Geophysical ilesearch Directorate, .June 15m.
No. t. Air-Coupled Flexural Awves in Floating Ice, l. l'ret. %1. Ewing, A. P. Crary, S. Kutz, j. Oliver,Geophysical ies.earch Directorate, November 1N50.
N o. Proeredings of the (inference on Ionospheric llesearch (June 1949), edited by Bradford 11.
Underhill and Ralph ;. Donaldson, Jr., (eophvsical itrmes rih Directorate, December 1950.
N $. Proceedings of te Colloquium on Meismpheri, Pkh'si a, eoited !,v N. C. Gerson, Geophysics
llea-earc4 I)ivision, July 151
No. 9. 'Th, Dispersion of Surface %ivem on %lult,-l o. r, in M , Norman A. iaskell, Geophysics Re-search l)ivision, August 1951.
No. ! 0. The Mea',rement -,f Stratompheric l)ensit, l)istr bution With the Searchlight Technique, L.Flterman, ,eophym.i e.. rllrerh Iivimion, l)ecembler 1Q51.
No. it. P ceedings of the Conference on Ionompheric Plhvsics (July 1950) Part A, edited by N. C. Gerson
1111 aii h J. Donaldson, Jr.. (,eojphvsiC-. Rleseorch Division, April 1952.
No. 12. Prceedings of the (:onference .' Ionospheriv Phvsics (July 1950) Part B, edited by Ludwig
Katz and N. C. (Gcrson, (eophvmic, o iearch )i .i ion, April 1952.
No. 13. Proceedings of the Colloquium on i,'.ae Mete.iologv, Aerosols and Cloud Physics, editedby Ralph J. Donaldson, Jr., (.eophvsics HIene&-h Division, May 1952.
No. 14. Atmospheric Flow Patterns and Their Representation 1. Spherical-Surface Harmonics, B. llaurwitzand Richard A. Craig, Geophysics Research I)ivision, Juiy 1Q52.
No. 15. Buck-Scattering of Electromagnetic Waves From Spheres and Spherical Shells, A. L. Aden, Geo-plysics Research Division, July 1952.
No. 16. Ntes on the Theory of Large-Scale l)isturbances in Atmospheric Flow With Applications toNumerical Weather Prediction, Philip Duencan l'hompson. Major, I. S. Air Force, GeophysicsResearch Division, July 1952
s.yJ. ": . IIFSEARCII PAPERS (Continued)
No. 17. The Observed Mean Field of Motion of the Atmv,,L ..-re, 1'..ip Mintz and Gordon Dean, GeophysicsResearch Directorate, August 1952. .. 2
No. 18. The Distribution of Radiational Temperature Change in the Northern Hemisphere lur gr ,Julius London, Geophysics Research Directorate, December 1952.
No. 19. Intemational Symposium on Atmospheric Turbulence in the Boundary Layer, MassachusettsInstitute of Technology, 4-8 June 1951, edited by E. W. Hewson, Geophysics Research Directo.rate, December 1952.
No. 20. On the Phenomenon of the Colored Sun, Especially the "Blue" Sun of September 1950, RudolfPenadorf, Geophysics Research Directorate, April 1953.
No. 21. Absorption Coefficients of Several Atmospheric Gases, K. Watanabe, Murray Zelikoff and EdwardC. Y. N, Geophysics Research Directorate, June 1953.
No. 22. Asymptotic Approximation for the Elastic Normal Modes in a Stratified Solid Medium, Norman A.Haskell, Geophysics Reseach Directorate, August 1963.
