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Archived

Avalanche Forecast

Mar 18th, 2012–Mar 19th, 2012
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Kootenay Boundary.

Danger ratings could be a notch higher is there is prolonged sunshine on Monday.

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Monday: Unsettled conditions with flurries or periods of snow, and possible sunny breaks (2-5cm). The freezing level should be around 1000-1200m. Winds will be moderate and gusty from the SW. Tuesday: Light to moderate snow - 5-15cm. The freezing level is around 1000m during the day and valley bottom overnight. Winds are moderate to strong from the SW. Wednesday: Unsettled conditions with cloudy skies and light flurries. The freezing level is around 800-1000m. Winds ease to light from the SW.

Avalanche Summary

Recent avalanche activity includes one Size 2 accidentally triggered avalanche. It occurred in relatively well-supported treed terrain on a north aspect. The skier triggered the avalanche in a shallow rocky area. There was also a report of a Size 3.5 avalanche on Saturday that was remotely triggered by a snowcat. This occurred just north of the region in the southern Purcells. It highlights the potential for triggered very large and destructive avalanches. Other observations on Saturday include several loose snow avalanches up to Size 2 on all aspects and skier controlled or explosive controlled avalanches up to Size 2 with 10-150cm deep crowns.

Snowpack Summary

Rain fell to around 2000 m on Thursday afternoon and froze into a crust on all aspects below this elevation. 10-30cm of new snow now sits above the crust. The previous storm snow overlies a sun crust on southern aspects and maybe a spotty 2-6mm surface hoar on north and east aspects, down around 60cm. Below that, the more significant early February surface hoar is down 80-140cm. Snowpack tests show moderate to hard forces generating sudden planar shears on this layer. Below the early February surface hoar layer, the snowpack is strong in most places. Cornices are growing and would act as a significant trigger for all the layers mentioned above if they drop.

Avalanche Problems

Wind Slabs

Fresh wind slabs are forming on lee and cross-loaded features in response to new snow and loading by SW winds. Old wind slabs are now buried but could enhance the size of potential releases on a variety of aspects in exposed areas.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 4

Deep Persistent Slabs

The deep nature of the mid-February surface hoar layer makes potential avalanches triggered on this layer large and destructive.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 2 - 7

Cornices

Cornices are very large and may fail with daytime warming, especially with sunny breaks. There is potential for triggering deep slabs on underlying slopes.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 6