Avalanche Forecast

Issued: Dec 30th, 2011 9:37AM

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

Avalanche Canada triley, Avalanche Canada

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Monday

Weather Forecast

The snow from Friday should have stopped by Saturday morning, leaving about 10 cm in the Nelson area and closer to 15 cm further south. Saturday should be mostly clear and a bit cooler, but still warm for this time of year. The freezing level is expected to be 700 metres on Saturday, and rising to 1000 metres on Sunday. The next system is forecast to hit the coast on Sunday. High cloud is expected to move in from the Northwest during the day, and may turn to snow by Monday morning. Forecast snow amounts are uncertain for Monday. Some models show the precipitation being confined to the coast.

Avalanche Summary

The recent natural avalanche cycle continues to produce natural and human triggered avalanches up to size 3.0. These occurred on all aspects above 1700m with wide propagations, and crown depths up to 80cms. 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 storm slab continues to develop. There is now 50-80 cm above the mid-december weak layer of surface hoar. The wind has been strong at times during the recent storms, and has built stiff wind-slabs in the alpine and at treeline on North, East and in some locations South aspects. Warm temperatures have developed a soft slab in the storm snow in areas that were not affected by the wind. The surface hoar layer continues to provide easy and sudden shears in tests. The mid-pack is generally well settled. Facets at the base of the snowpack have not been reactive recently.

Problems

Persistent Slabs

An icon showing Persistent Slabs
New snow has increased the slab depth to 60-80 cm above the weak surface hoar layer. Natural avalanches and light triggers have resulted in wide propagations and large destructive avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 6

Wind Slabs

An icon showing Wind Slabs
Be alert for wind slabs below ridge crests, behind terrain features, and in cross-loaded gullies. New cornices may be weakly bonded and likely to break off.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Storm Slabs

An icon showing 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 31st, 2011 8:00AM