Avalanche Forecast

Issued: Dec 29th, 2011 9:24AM

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

swerner, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Friday

Weather Forecast

Friday: Snow amounts 10-15cms. Ridgetop winds 40km/hr from the West. Freezing levels could rise to 1100m. Saturday/Sunday: A ridge of high pressure is expected to move into the region for the weekend. Mainly sunny skies, and light-moderate winds from then NW.

Avalanche Summary

We are now in an avalanche cycle with numerous natural avalanches occurring, reported up to size 3. These occurred on all aspects above 1700m with wide propagations, and crown depths up to 50cms. Many of these are failing on the mid-December surface hoar, mostly on north through east aspects from 1500m to the peaks. A skier remotely triggered an avalanche from 50m away and in many places shooting cracks and whumphing are further indicators of a very touchy, unstable snowpack.

Snowpack Summary

The snowpack is in a very touchy state. 30-50cm of storm snow has built up over a weak old snow surface. The storm snow has turned into a soft slab due to warming. South-west winds have led to the development of wind slabs on lee slopes. The surface hoar layer buried in mid-December is now under 45-70cm of snow and is highly reactive. It is well-preserved with 10-15mm crystals and exists into alpine start zones (although it's probably best preserved in sheltered areas near treeline). The mid-pack is generally well settled. Facets exist at the base of the snowpack.

Problems

Persistent Slabs

Enough snow has built up above a very touchy buried surface hoar layer that we are seeing many avalanches fail on this layer.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 6

Wind Slabs

Be alert for wind slabs below ridge crests, behind terrain features, and in cross-loaded gullies.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Storm Slabs

Recent snow has fallen with a warming trend. This is likely to have created slab conditions within the new snow. A storm slab could step down to a persistent weak layer, creating a large avalanche.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Valid until: Dec 30th, 2011 8:00AM