Avalanche Forecast

Issued: Dec 3rd, 2012 8:37AM

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

Peter, Avalanche Canada

South Columbia.

Summary

Confidence

Poor - Due to limited field observations

Weather Forecast

Synopsis: A frontal system will move through southern BC on Tuesday bringing moderate snow, very strong winds, and rising freezing levels. Unsettled and cooler conditions are expected in the wake of this system. Tuesday: Moderate snow – 15-20 cm; the freezing level could jump to 1500 m; winds are very strong from the southwest. Wednesday and Thursday: Cloudy with flurries; the freezing level lowers to near valley bottom.

Avalanche Summary

Several natural avalanches up to size 2.5, and skier controlled avalanches up to size 2 were reported over the weekend. A natural avalanche cycle was observed primarily on Saturday. Expect avalanche activity to increase again on Tuesday with forecast wind and snow.

Snowpack Summary

Up to 70 cm of moist storm snow has fallen in the past several days. This snowfall was accompanied by generally moderate south-southwest winds, forming wind slabs in exposed leeward terrain. Below the storm snow may be a layer of surface hoar or a thin crust. There are no new snowpack tests on this layer and recent reports describe the surface hoar as being small and spotty.Deeper in the snowpack you might find a second thin surface hoar layer about 100cm down. As well, the early November rain crust now sits over 120cm down in most locations (at treeline and above) and may exist in combination with facets. Recent snowpack tests give occasional hard sudden collapse (Drops) results on the early November layer. There is potential for this layer to wake up with continued loading from snow and wind, or for storm slabs to "step down" creating a very large and destructive avalanche.

Problems

Wind Slabs

Deep and dense wind slabs are likely in exposed lee slopes and cross-loaded gullies well below ridge crests.

Avoid lee and cross-loaded terrain near ridge crests.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

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

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 5

Storm Slabs

Instabilities may exist within or under the recent storm snow (up to 70cm) and may be triggered naturally or by the weight of a person.

Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>Stick to simple terrain and be aware of what is above you at all times.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

2 - 5

Persistent Slabs

Deeper persistent weak layers may wake up with continued loading and forecast warming. Storm slabs may also "step down" to these weaknesses, creating a very large and destructive avalanche.

Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Dec 4th, 2012 2:00PM