Avalanche Forecast

Issued: Dec 20th, 2012 9:53AM

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

jlammers, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Overnight Thursday and Friday: Light snowfall / Light to moderate southeast winds / Temperature inversion with ridgetop temperatures of -12.0Saturday: Mostly clear / Light southeast winds / Temperature inversion with ridgetop temperatures of -12.0Sunday: Trace amounts of snowfall / Light east winds / Ridgetop temperatures of -16.0

Avalanche Summary

Size 1 slabs have been reported from the south of the region, while slabs to size 2.5 were reported from steep alpine chutes in the Bear Pass area. All activity is suspected to have occurred within recent storm layers.

Snowpack Summary

Very light amounts of new snow have been redistributed by winds at higher elevations. This overlies the past week's storm snow which is settling rapidly, although weaknesses may still exist within storm snow interfaces. A buried surface hoar layer, reported to be 5 to 10mm thick, recently produced sudden snowpack test results down 60-80cm in the Shames backcountry, and may exist in other areas too. Avalanche professionals continue to monitor a faceted crust near the ground. It seems this problem is confined to alpine areas and likely needs a large trigger and/or a shallow snow pack feature to trigger. Cornices are also really big and forecast strong winds and cooling temperatures could make them especially heavy and brittle.

Problems

Storm Slabs

Light amounts of new snow have been redistributed by strong winds into wind slabs on a variety of aspects. These wind slabs are adding to older storm snow accumulations which have most likely gained considerable strength.

Be cautious as you transition into wind affected terrain.>Use caution in areas that have been reverse loaded by winds.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

A persistent weak layer of surface hoar, buried 60-80 cm below the surface has been reported from around Shames. Although triggering seems less likely, watch for convex rolls in sheltered areas where the SH may have been preserved.

Be aware of the potential for large avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

Deeply buried weaknesses exist. Large triggers, such as cornice falls, could release deeper avalanches on steep, smooth terrain, especially in thinner snowpack areas.

Conditions are greatly improved, but be mindful that deep instabilities are still present.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Dec 21st, 2012 2:00PM