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Archived

Avalanche Forecast

Mar 11th, 2012–Mar 12th, 2012
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
4: High
The avalanche danger rating below treeline will be high
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: South Coast.

Monday's danger ratings are based on the arrival of a heavy storm. Timing of this system is very uncertain. The ratings can be dropped to considerable if it's not snowing or blowing significantly.

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Monday: A deep Pacific low spreads moderate to heavy snow to near valley floor (25-30cm). Severe winds and thunderstorms are possible. The timing and intensity of this system are uncertain.Tuesday: Light convective snow. Moderate winds, gusty at times. Freezing level around 600m.Wednesday: The next low pressure system arrives with moderate snow, strong south-westerly winds and freezing level rising slightly.

Avalanche Summary

A few cornice-triggered and small skier-triggered slabs in the size 1-2 range have been reported since it began snowing on Friday. Earlier in the week, warming prompted a widespread natural cycle in the Coquihalla and skiers triggered very touchy persistent slabs at low elevations. An unnervingly large natural avalanche cycle occurred last weekend, with slabs up to size 4.5 propagating 2-3km along ridgelines and stepping down to the mid-February layer. Similar avalanches are possible as storm loading continues this week.

Snowpack Summary

Strong winds and new snow are expected to create new wind slabs and storm slabs which are likely to fail in steep terrain, and could overload persistent weak layers. Persistent weak layers are variable in distribution across the region. A hollow series of poorly-bonded crusts was reported on southerly aspects in the Duffey Lake and Chilcotin regions last week, which may have healed somewhat with dramatic warming at the end of the week. A lower weakness comprising surface hoar, facets and a crust, has produced whumpfs and still is a key concern for step-down avalanches in many parts of the region. It is especially prevalent on south-facing slopes above treeline, and all slopes below treeline.

Avalanche Problems

Storm Slabs

Forecast heavy snow may create a widespread storm slab problem. Initial reports indicate a weak interface in the recent storm snow. Be cautious with sluffing in steep terrain as well.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Very Likely

Expected Size: 2 - 6

Wind Slabs

New and old wind slabs exist on a variety of slopes. Forecast extreme wind speeds may create wind slabs unusually low on the slope. Large cornices also threaten some slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 5

Persistent Slabs

Continued diligence and conservative decisions are necessary. The potential for cornice triggers, remote triggering, step down avalanches, and wide propagations makes this problem particularly tricky to manage.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 4 - 8