52

A PILOT AVALANCHE FORECASTING PROJECT FORTHE CRAIGIEBURN RANGE, NEW ZEALAND

B. B. FitzharrisDepartment of Geography, University o f Otago, Dunedin.

INTRODUCTION

The rising use of our mountains has high-lighted the need for an avalanche forecastingsystem. As shown by Prowse et al. (1981), thenumber of deaths from this hazard increasedmarkedly in the decade from 1970 to 1979.

In his assessment of avalanche problems inNew Zealand, La Chapelle (1979) noted:

An important factor i n t h e current hazardtrend has been the climate pattern o f the lastdecade. I n most areas this has been marked bymild winters w i t h relat ively l i t t l e snowfall.Avalanche act iv i ty has been correspondinglylight during just that period when winter re-creation activities have taken a strong upsurge,leading i n many cases t o a dangerous com-placency about avalanche dangers. I f a climatechange leading to heavier snowfalls o r colderconditions w i t h l o w e r snowlines, o r b o t h ,should come to pass, the avalanche hazard wi l labruptly rise a t a much faster rate than theincrease in winter recreation.

D. McNultyPorter Heights Skifield, Canterbury.

and I . D. MillerNew Zealand Meteorological Service, Christchurch.

Weather and Climate (1983) 3: 52-58

I. F. OwensDepartment o f Geography, University o f Canterbury, Christchurch.

ABSTRACT

The need for an avalanche forecasting system in New Zealand is brieflydiscussed and options relating to approaches to forecasting are outlined. TheCraigieburn Range pilot project which operated during the 1982 winter isdescribed by reference to participants, meteorological snow and avalancheobservations, the New Zealand Meteorological Service role, the daily routine,and content and dissemination of avalanche forecasts.

A public avalanche forecast system is onemethods o f reducing the avalanche hazard.Notification o f current snow stability, andwarnings of possible changes over the next 24hours that are likely t o be caused b y theweather, might prevent foolhardy behaviour inthe mountains and increase safety in ski opera-tion management.

The New Zealand Mountain Safety CouncilAvalanche Committee recognises four areaswhere the hazard is greatest: the Te Anau-Milford highway, the Mount Cook region, theCentral North Island skifields and the Canter-bury skifields. Ultimately, specialized ava-lanche forecasts might be prepared for eachof these areas, with another more generalisedforecast for other less frequented areas of themountains. To identify difficulties and costs ofimplementing such an avalanche forecastingscheme, a pi lot project was begun i n the

Avalanche Forecasting 5 3

35°S

40*S

44*S

i68° E

0 1 2 3 41 t

Contour interval 2 0 0 m

•••••1 State Highway 7 3

Fig. 1 : Location o f the study area.PH — Porter Heights, WWSC — Windwhistle Winter Sports Club, CWSC — Canterbury Winter Sports Club,BRSC — Broken River Ski Club, SB — Ski Basin Meteorological Station, CP' — Craigieburn Forest ParkHQ, CVSC — Craigieburn Val ley Sk i Club.

54

Craigieburn Range (Fig. 1) i n the winter of1982. Choice of this location has the followingadvantages:

(a) I t is a high avalanche hazard area;(b) Numerous skifields can provide dailyinformation o n local weather, snow andavalanche activity;(c) The climate and snowpack o f t heCraigiebum Range i s better documentedand understood than most other New Zea-land mountain areas (Prowse, 1981);(d) The New Zealand Meteorological Ser-vice regional office in Christchurch has akeen interest i n mountain meteorology;(e) Most communications can be made bypublic telephone;

Avalanchehazard

evaluat ion

Avalanchehazard

forecast

Highlyunstable

Increasingavalanche

potential

G.EFFECT OF

PROJECTEDWEATHER?

Moreunstable

I.INCREASING (MOD-HIGH

-EXTREME) AVALANCHEHAZARD

Lessunstable

4- Ma rginal-4-

NATURE O F A N AVA L A N C H EFORECASTING SYSTEM

The most important factors controllingavalanches are weather, snow and terrain. Thehazard they create depends on the activity ofman who can not only be struck by avalanchesbut can also trigger them. To produce anavalanche forecast, it is first necessary to makean evaluation of the hazard, then assess pos-sible changes in the light of forecast weather.Two main approaches are commonly em-ployed:

A.

IS AVALANCHING POSSIBLE?(Is there suff ic ien t snow)

1Yes

B.CURRENT SNOWPACK

S TA B I L I T Y ?

C 5 r )Unstable S t a b l e

D. C .EFFECT OF PRESENT M a r g i n a l E F F E C T OF PRESENT

WEATHER? W E A T H E R ?

C 5Moreunstable

F.EFFECT OFPROJECTEDWEATHER?

Lessstable

(f) Back-country usage of the area duringwinter months is increasing but is still at asufficiently low level to allow a trial oper-ation of the system.

Marginal

Morestable

Less stable

Less unstable

Fig. 2 : Steps i n avalanche hazard evaluation a n d forecasting.

Lessstable

* - Marginal

Avalanche Forecasting

Morestable

Decreasingavalanche

potent ia l

E.EFFECT OF

PROJECTEDWEATHER?

Morestable

DIMINISHING OR LOWAVALANCHE H A Z A R D

Avalanche Forecasting

(a) Causal-intuitive approach: a knowledgeof physical cause and effect i n the snowcover is used to deduce, i n a qualitativeway, the conditions of snow instability.(b) Statistical: a quantitative analysis o faccumulated data on past weather, snowand avalanche patterns is used to predictfuture avalanche occurrences.

At present, there are not sufficient data toapply the second approach in the CraigieburnMountains. Any pilot scheme must thereforebe based on the causal-intuitive approach. Aforecasting method using such an approach isoutlined in Fig. 2 (Businger et al., 1980). Thefirst task, that o f assessing snow stability, isusually based on six kinds of input:

(i) Snow cover distribution;(ii) Current and past avalanches;(iii) Snowpack structure;(iv) Local meteorological inputs;(v) Weather service information;(vi) Ski and explosive tests.

A pilot scheme must contain these inputs, plusa knowledgeable experienced person to inte-grate them on each skifield so that the currentsnowpack stability is assessed. The other stagesin the scheme involve assessing the effect ofpresent weather (stages C and D in Fig. 2)and of projected weather (stages G, F and E),which must involve the meteorologist in co-operation with an avalanche expert.

OPTIONS FOR AVA L A N C H E FORECASTINGSCHEMES

Avalanche forecasting schemes operate i na number o f countries. Those i n Canada,U.S.A., Norway, Switzerland and Australiahave been examined by members of the Ava-lanche Committee. I t is apparent that a rangeof options i s available, depending on suchfactors as finance, scale of the hazard, popu-lation in the mountains, government commit-ment, snow conditions and climate. Someoptions are unsuitable for New Zealand withits small population, limited resources andlargely uninhabited mountains.

A range of avalanche forecasting systems,in order o f decreasing amounts o f centralmeteorological input, is as follows:(a) Centralized forecasts based o n l y o nmeteorology (as practised in Norway). The onlyinformation available is meteorological, such

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as that based on synoptic weather reports,satellite photographs and upper air soundings,that go towards the routine weather forecast.The avalanche forecast, which is based onprojected weather alone, is issued from theNational Weather Centre. Thus an anticipatedheavy snowfall, or rapid warming, might giverise to a forecast of high avalanche risk. Thesystem can operate with little additional in-formation but has no input of avalanches. Tocounter this, t he Norwegians obtain somesnowpit information immediately prior to holi-day periods, so that the reliability o f theavalanche forecast can be improved when themountains are most populated.(b) Centralised forecasts based o n meteo-rology and mountain weather and snow reports(as practised in Colorado and Switzerland). Amajor communication network is establishedto relay daily observations about weather andsnow conditions in the mountains to a centralforecasting establishment. Either people musttake these observations and thus live in themountains, o r data must be obtained fromautomatic weather stations, a n expensiveproposition. The central forecasting establish-ment also receives detailed, updated meteo-rological forecasts and maps o f regional andhemispheric weather patterns.

The system is effective, but is expensive toestablish and maintain, and requires largemanpower reserves. As such, i t is not suitablefor New Zealand. Furthermore, the centralizedavalanche forecaster must develop a feel foravalanche conditions many kilometres away,and unless he is very experienced and has agood knowledge o f a l l important mountainranges and their avalanche paths, his forecastcan be awry.(c) Centralised forecast based on meteorologyand strong field control (as practised in Wash-ington State, U.S.A.). This is similar to (b) buttends to be of smaller scale and directed to-wards specific areas. The meteorologist whomakes the forecast is also an avalanche expertwho a t regular intervals observes snow andavalanche conditions in the mountains. This isan excellent system, but i t is expensive andrequires a high level o f expertise on the partof the forecaster.(d) Forecast based on local observation, butwith strong meteorological input (similar tothat practised in Utah, U.S.A.). Observationsof snowpack, mountain weather and avalanche

56

activity are made near the hazard area andrelayed to a central co-ordinator. He assessesthis information and discusses it with a weatherforecaster. Together they arrive at a consensusas to the avalanche forecast which is thus ateam effort combining accurate weather in-formation and field observations with know-ledFable interpretation. Considerable trainingin snow p i t analysis and avalanche hazardevaluation is needed by the weather forecasterto establish the necessary rapport between him-self and the observers. Likewise, the centralco-ordinator needs to develop his knowledgeof meteorology t o better understand t h elanguage o f the weather forecaster. Both o fthem poo l the i r expert knowledge i n a nattempt to see the total picture.(e) Forecast based largely on local observa-tion wi th a minimum of meteorological input(as is current practice in New Zealand). Ob-servations of varying degrees of sophisticationare made locally. These may range from acasual noting of weather and snow conditionsto extremely detailed, regular observations bya team of technicians as occurs at Rogers Pass,Calada. T h e meteorological input t o t h eavalanche forecasting procedure is often mini-mal, consisting of the local weather forecast asheard on radio (which is usually for lowlandareas) o r possibly a generalized mountainweather forecast. At best, this system can makegood evaluations o f snowpack stability, bu tforecasting ability is severely constrained by01- lack of meteorological information from abroader data base.

Of these systems, option (d), a forecastbas-xl on local observation but with a strongmeteorological input, seems most appropriatefor New Zealand. Capital costs are modest, i tcan operate within existing organisations, andthe necessary expertise is available with a smallamount of training. The avalanche forecast isin the hands of the avalanche forecaster whoworks in the mountains and understands thebehaviour of the avalanche paths better thananyone else.

OUTLINE OF THE PILOT PROJECT1 GENERAL

The participants i n t h e proposed p i l o ts-heme are the N.Z. Mountain Safety CouncilAvalanche Committee, N .Z . MeteorologicalService, Porter Heights Ski Area, Broken River

Avalanche Forecasting

Ski Club, Canterbury Winter Sports Club,Craigieburn Val ley S k i Club, WindwhistleWinter Sports Club and the N.Z. Forest Ser-vice. The project co-ordinator is Dave Mc-Nulty, resident a t Porter Heights Skifieldwhich is the forecast centre.

Daily assessment and 24-hour forecasts o favalanche hazard are based on the followinginputs:

(a) Daily weather, snow and avalanche in-formation from ski area observation sites;(b) Snowpack data collected by the fore-caster and observers at regular intervals;(c) Specialised weather forecasts f o r thearea provided by the Christchurch AirportOffice of the N.Z. Meteorological Service;(d) Correlation a n d assessment o f a l lweather, snowpack and avalanche data.

2. OBSERVATIONS AND EQUIPMENTAt each observation site, one person has

been trained and appointed to the task of col-lecting and recording daily readings,* and com-municating these to the forecast centre. Eachsite has been provided with a standard set ofequipment and a specific study plot estab-lished for collection o f new snow data. Com-munications with the forecast centre on a twicedaily basis are by Post Office telephone linkor by radio link to Craigieburn Forest ParkHeadquarters at the northern end of the range.

3. METEOROLOGICAL SERVICE LIAISONAn excellent liaison between Porter Heights

and t h e Christchurch office o f t h e N .Z .Meteorological Service has already been estab-lished. Continuation o f this encompasses tit(following aspects:(a) L o a n o f basic instruments and supply o frecording forms. Some o f the skifields men-

* The basic 'observation k i t ' provided partly by theMeteorological S e r v i c e a n d p a r t l y t h r o u g hMountain Safety Council funding includes:

1 standard meteorological screen and stand;Maximum, minimum and dry bulb thermometers;4x4x2m snow fencing material;2 snow boards;I snow density k i t ;1 snow thermometer;1 crystal grid and lens;Recording forms.

Avalanche Forecasting

tioned above already have instruments andothers have been equipped w i th Stevensonscreens to house dry bulb and maximum andminimum thermometers o n condition tha tregular weather reports are provided.

A special field book and reporting form hasbeen designed for weather observation in themountains and is being used during the pro-ject. These are designed for the recording ofweather, snow conditions a n d avalancheoccurrence by people with little or no previousexperience. T h e field book i s suitable f o roccasional observations as might be made onback-country trips, while the reporting form ismore appropriate for repeated daily observa-tions at one site.(b) Provision of daily weather forecasts. Forthe past few skiing seasons, daily weather fore-casts have been provided for Porter HeightsSkifield in return for observations telephonedeach morning t o t h e weather office a tChristchurch Airport. During the 1982 seasonthe forecast was prepared each morning forthe whole o f the Craigieburn Range. Therewas no attempt to differentiate between con-ditions in different parts of the range, but thelarger network of observations may show thatthere a r e significant differences i n loca lweather.

The forecast is based on three-hourly sur-face weather reports f rom regular observa-tions throughout the South Island, six-hourlywind soundings from Christchurch, Dunedinand Invercargill made at midnight and/or mid-day and computer-based forecast maps fromthe National Weather Forecasting Centre i nKelburn. Since these maps show only broad-scale flow patterns, i t is necessary to monitorlocal changes in the airflow in the lowest 1000or 2000 metres, using pressure differences be-tween certain key stations such as Hokitikaand Christchurch, a n d Christchurch a n dDunedin.

Because of the importance of the amount ofnew snow and temperature changes t o theavalanche hazard, the forecaster endeavoursto emphasize the amount o f snow (or rain)expected, wind speed and direction at ridge top(about 2000 m) and height o f the freezinglevel. However, i t must be borne in mind thatthere may be wide variations from one partof the range to another.

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(c) Archiving the data. The daily reports o fweather, snow conditions and avalanches fromthe six skifields will be entered in the Meteo-rological Service's data archive where i t wi l lbe available for future analysis.

4. WINTER ROUTINEObservations o f weather, s n o w a n d

avalanches began w i th the f i rst significantsnowfall.

The following outlines the daily routine:0630 Make routine weather and snow observa-tions at Porter Heights;0700 Prepare avalanche hazard assessment forPorter Heights Ski Area and direct controlmeasures as required;0800 Record morning data from observationsites;0900 Phone a l l weather data through t oChristchurch Meteorological Office and receiveweather forecast;0930 Review previous evening's avalanche haz-ard assessment and forecast for the Range;0900-1700 Field observations o f avalancheactivity and snowpack;1600 Record and correlate snow, avalancheand weather data from skifields;1645 Phone weather information through toMeteorological Office a n d receive weatherforecast;1800 Prepare avalanche hazard forecast fo rfollowing day;1930-2000 Disseminate forecast to ski areas.

5. THE AVALANCHE FORECASTEach forecast contains:(a) A n outline of current snowpack stabil-ity and hazard;(b) A n outline of the latest weather forecastfor the area;(c) A 24-hour forecast o f avalanche haz-ard based on current conditions and weatherforecast;(d) Occasional safety t ips pertaining t ocurrent conditions.

The hazard assessment and forecast shouldas far as possible specify the type and location(altitude, aspect etc) o f avalanches that maybe expected. The terminology used for describ-

58 A v a l a n c h e Forecasting

ing the degree of hazard should be based onthe following which is currently being used inthe United States:

Low Avalanche Hazard — mostly stablesnow exists and avalanches are unlikely ex-cept i n isolated pockets o n steep snow-covered slopes and gullies. Back-countrytravel is generally safe in areas with lowhazard.Moderate Avalanche Hazard — areas o funstable snow exist and avalanches are pos-sible on steep snow-covered open slopes andgullies. Back-country travellers should usecaution in areas of moderate hazard.High Avalanche Hazard — mostly unstablesnow exists and avalanches are likely onsteep snow-covered slopes and gullies. Back-country travel is not recommended exceptin avalanche-free areas.Extreme Avalanche Hazard — widespreadareas of unstable snow exist and avalanchesare certain o n steep snow-covered openslopes a n d gull ies. L a r g e destructiveavalanches are possible. Back-country travelshould be avoided.

6. SAMPLE FORECASTAvalanche Forecast for Craigieburn Moun-

tains (excluding developed ski areas withavalanche control).

Date: 17th September, 1981. Prepared a t0900.

(Snowpack Condition). Large grains of oldtemperature-gradient snow under ly s t ronghard slabs i n most areas between 1500 and2000 m. However, the snowpack is generallystable a t the present due to relatively coolconditions persisting since a moderate warm-ing cycle a week ago.

(General Stability and Forecast). The cur-rent hazard is low on north aspects and mod-erate on south aspects which have large accum-ulations of snow.

The weather is expected to remain fine withlight to moderate SW winds and cool air tem-

peratures fo r the next 24 hours, thus l itt lechange in snow stability is expected.

(Safety t ip). Travellers a re warned thatsteep open slopes should be crossed by no morethan one person at a time.

7. DISSEMINATION OF FORECASTSFor the purposes of the pilot project, i t is

not intended to distribute the forecasts on adaily basis beyond the participants in the pro-ject. The forecasts are being produced in writ-ten form and stored for later evaluation.

CONCLUSION

Although the forecasting project outlined inthis paper is ambitious in scope, indications sofar suggest that i t has every chance o f suc-cess. A l l skifields involved have reactedenthusiastically, and other interested partiessuch as the New Zealand Forest Service haveoffered valuable support. The winter of 1982was characterised b y significant avalancheactivity and a broad review of the success ofthe forecasts indicates that none were seriouslyawry. More detailed evaluation of the successof the forecasts is currently under way. Dis-cussion of the results of this exercise and ofbroader questions, such as continuation of thescheme, and means and funding of dissemin-ation o f forecasts, is planned for a seminarinvolving al l interested groups scheduled t otake place in time to allow planning for the1983 winter.

REFERENCES

Businger, S . , M o o r e , M . a n d M a r r i o t t , R . , 1 9 8 0 :Northwest avalanche forecasting project. Paperpresented t o Avalanche Workshop, Vancouver,British Columbia.

La Chapelle, E . R . , 1979: A n assessment o f ava-lanche problems i n New Zealand. New ZealandMountain Safety Council, Avalanche CommitteeReport N o . 2, 53 pp.

Prowse, T. D., 1981: The snow environment o f theCraigieburn Range. Unpublished Ph.D. thesis,University o f Canterbury, 359 pp.

Prowse, T. D., Owens, I . F. and McGregor, G. R.,1981: Adjustment t o avalanche hazard i n NewZealand. N e w Zealand Geographer, 37: 25-31.