Avalanche Forecast

Issued: Dec 28th, 2011 9:10AM

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

pgoddard, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Wednesday night: 10-15cm. Moderate to strong west to south-west winds. Freezing level lowering to 1300m.Thursday: Light snowfall. Light-moderate north-westerlies. Freezing level around 900m.Friday: Moderate to heavy snow. Strong south-west winds. Freezing level around 1000m. Saturday: Light flurries. Cooling temperatures. Light north-westerly winds.

Avalanche Summary

We are now in an avalanche cycle with numerous natural and human-triggered avalanches occurring, reported as up to size 2.5. 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

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, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

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 - 3

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 - 5

Valid until: Dec 29th, 2011 8:00AM