Avalanche Forecast

Issued: Dec 11th, 2012 9:23AM

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

slemieux, Avalanche Canada

South Columbia.

Summary

Confidence

Fair

Weather Forecast

A weak ridge moving over the region should bring lighter precipitations for Wednesday and then mainly cloudy skies in the Southern part of the region and partial clearing in the Northern part. The next system is weaker and should reach the region later Thursday and deliver some light to moderate precipitations and stronger Southwesterly winds for the rest of the period. Cool temperatures (-12 C) and lighter winds are expected for Friday.

Avalanche Summary

A few small soft slabs were triggered by skiers yesterday on the storm snow. Suspect recent sluffing in steep terrain.

Snowpack Summary

20-30 cm of warmer-denser new snow from the past few days fell on a cooler-lower density storm layer possibly creating storm slabs and also burying older windslabs. The moderate to strong North West and South West winds most likely created new windslabs on leeslopes in the alpine and at treeline. The bond within the new snow with the older storm snow interface is unknown, but it still remains a concern in the alpine and at treeline on lee slopes. There has been report of multiple significant results (sudden planar) on the Late November surface hoar layer now down around 100 cm and 150 cm in snowier areas. The early November crust is still a concern and is producing more varied results from break to sudden planar. Large planar slopes with known smooth ground cover are areas to avoid in respect to this concern.

Problems

Storm Slabs

Thick wind slabs are also to be expected in the alpine and at treeline on Easterly aspects. Heavy sluffing may be experienced in sheltered terrain.

Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 5

Persistent Slabs

The weak layer is buried down about 100 cms and recently has been loaded by new snow and wind. Wind slabs above may trigger this deeper layer in unsupported terrain. Elevations between 1600-2100 metres are the most suspect.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Deep Persistent Slabs

The early November rain crust is deeply buried. This layer appears to be very drainage dependant, and there have only been a few avalanches reported across the region. Releases on this layer will be very large and destructive.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

4 - 7

Valid until: Dec 12th, 2012 2:00PM