Post on 31-Dec-2015
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Anticipating Aviation Weather Anticipating Aviation Weather Hazards in the SouthwestHazards in the Southwest
Dr. Curtis N. JamesDr. Curtis N. JamesDepartment of MeteorologyDepartment of Meteorology
Prescott, ArizonaPrescott, Arizona
OverviewOverview
• What are some general characteristics of the climate of the Southwest?
• How is aviation affected by this climate?
• How can the aviation weather hazards be anticipated and avoided?
• Why is an understanding of the vertical structure of the atmosphere necessary?
General Climate of the SouthwestGeneral Climate of the Southwest• Located in a latitude belt (~30°) where air generally sinks
and warms (usually clear & dry; 300+ flying days / year)• Rugged terrain (clouds/precip usually more frequent over
windward slopes w/ lee rain shadowing & waves)• Continental climate, isolated from oceans by terrain
(generally dry air w/ high temperature variability)• Prevailing surface wind generally southwesterly (except
where terrain generates local winds)• Prevailing wind aloft westerly in cold season, southerly in
summer (associated with the SW monsoon)• In warm season, deep convective layer near the ground
Aviation Hazards of the SouthwestAviation Hazards of the Southwest
• Deep convective boundary layer– Low-level turbulence and dust devils
• Thunderstorms (esp. July – September)– Downbursts (especially dry microbursts)– Hail, lightning, turbulence near thunderstorms
• Mountain waves / shears & lee turbulence • Other (icing, low clouds, IMC, LLWS, etc.)
Related to the vertical structure of atmosphere
Deep convective boundary layerDeep convective boundary layer
20,000’ MSL or more
(more stable air above)
Hot, dry, unstable air
dust devil
thermal thermal
Convective boundary layer (Prescott, AZ)Fall 2000—Photo by Joe Aldrich
Dust Devil in Arizonawww.nasa.govwww.nasa.gov
Mountain
Strongest wind speed
Mountain wavesMountain waves
Roll cloud
Lee waves
Dust may be visible
ACSL clouds
Cap cloudCloudy,
cooler, possible fog & precip
Clear, warm, dry & windy
Mountain wave clouds (PRC) 2000—Photo by Ben Small
Lenticular clouds (near Denver) 2000—Photo by Josh Richmeier
Dry microburstsDry microbursts
• When precipitation falls through unsaturated air, evaporative cooling may produce dry microbursts
• Result in very hazardous shear conditions• Visual clue: fallstreaks or virga (fall streaks that
don’t reach the ground)
Flight path of plane
45 kt downburst
45 kt headwind
45 kt tailwind
Downburst (Phoenix, AZ)July 2003—Photo by Phillip Zygmunt
Downburst (Prescott Valley, AZ)1999—Photo by Jacob Neider
KPRC 081953Z 19008G15KT 160V220 10SM CLR 29/01 A2999 RMK AO2 PK WND 13027/1921 SLP060 VIRGA N-E TCU W-SE T02890006KPRC 082053Z 25011G17KT 10SM CLR 32/M01 A2998 RMK AO2 SLP052 T03221011 56010KPRC 082153Z 25013G18KT 10SM CLR 32/M01 A2996 RMK AO2 SLP048 ACFT MISHAP T03171006
ERAU Aircraft #N519ER
08 June 2003
Virga
ERAU Aircraft #N518ER29 November 2003
Downslopewind?
Stable air over less stable air, increasingwind speed with height
Kingman, AZ
Vertical structure of atmosphereVertical structure of atmosphere
)(
.)(exp
)(1000
22
286.0
RichardsonBulk
zV
zU
zTg
R
temppotentialequivalentTc
wL
etemperaturpotentialp
T
b
p
ve
The following three parameters can be used to anticipate most of the hazards in a forecast vertical sounding:(Analysis Tool: http://meteo.pr.erau.edu/links.php)
(http://rucsoundings.noaa.gov/gifs/)
ALT PRES DIR SPD TEMP DEWP LAYER MECH THERM CLOUD CLOUD
ft mb C° kt C C ft (MSL) TURB? TURB? LAYER LCL (ft)
4895 845 144 22 24 4.3 4895 - 4950 TURB TURB
4950 843 143 24 23 4.3 4950 - 5068 TURB TURB
5068 840 144 25 22.6 4.2 5068 - 5246 TURB TURB
5246 835 145 26 22 4.1 5246 - 5479 TURB
5479 828 145 27 21.3 4 5479 - 5836
5836 817 147 27 20.2 3.7 5836 - 6197 TURB TURB
6197 807 148 27 19.1 3.5 6197 - 6558 TURB TURB
6558 797 150 27 18 3.3 6558 - 6925
6925 786 151 26 17 3.1 6925 - 7296 TURB TURB
7296 776 153 26 15.9 2.8 7296 - 7667 TURB TURB
7667 766 156 25 14.8 2.5 7667 - 8044
8044 755 158 24 13.7 2.2 8044 - 8425 TURB TURB
8425 745 162 23 12.6 1.8 8425 - 8809
8809 735 167 22 11.6 1.3 8809 - 9199
9199 724 173 21 10.6 0.6 9199 - 9593 TURB
9593 714 189 18 9.6 -0.4 9593 - 9990 TURB
9990 704 213 18 8.8 -2.6 9990 - 10141 TURB 12,775
24330 400 259 42 -25.6 -28.2 24330 - 24888 CLOUD
24888 390 254 43 -27 -29.2 24888 - 30561 CLOUD
Potential Temperature and Equivalent Potential Temperature Profiles
0
10000
20000
30000
40000
50000
60000
260 280 300 320 340 360 380
Temperature (Kelvins)
Hei
gh
t (F
eet) θ (Kelvins)
Dry parcel
θe,s (Kelvins)
Wet parcel
Dry thermals
Convectivelyunstable layer
WSR-88D Radar Images NM/Holloman AFB
SummarySummary
• The Southwest has a fascinating climate, with a number of aviation hazards
• Many hazards may be anticipated using a vertical profile of the atmosphere
• Suggest analyze forecast sounding prior to flight (http://rucsoundings.noaa.gov/gifs/)
• Spreadsheet tool is available on the ERAU Department of Meteorology website (http://meteo.pr.erau.edu/links.php)
Questions?