Avalanche Forecast

Issued: Mar 11th, 2012 10:37AM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Storm Slabs, Wind Slabs and Persistent Slabs.

Avalanche Canada pgoddard, Avalanche Canada

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.

Summary

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.

Problems

Storm Slabs

An icon showing 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

An icon showing 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

An icon showing 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

Valid until: Mar 12th, 2012 9:00AM

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