Avalanche Forecast

Issued: Mar 19th, 2012 10:18AM

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

Avalanche Canada swerner, Avalanche Canada

Another storm hits the region tonight into Tuesday. Strong winds and new snow has increased the avalanche danger.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Monday overnight brings 8-15 cm of new snow. This is accompanied by strong South winds, and freezing levels near valley bottom. Tuesday: Snow amounts 15-25 cm. Ridgetop winds strong from the SW. Treeline temperatures near -5. Freezing levels near 500 m. Wednesday: Due to the convective weather pattern, scattered light-moderate snow accumulations are expected. Ridgetop winds moderate from the SW. Treeline temperatures near -8. Freezing levels valley bottom. Thursday: Cloudy in the morning, broken skies in the afternoon. Light afternoon flurries near 5 cm. Freezing levels valley bottom in the morning, rising to 700 m in the afternoon.

Avalanche Summary

Last week was very active with natural avalanche activity up to size 3.5. Additionally we had several reports of rider involvements and close calls. Some were failing on the mid-February persistent weakness. The size and frequency of avalanches seems to have decreased slightly over the weekend as storm slabs and wind slabs slowly gained some strength. On Sunday a skier accidently triggered a size 1.5 from a NE aspect, in steep rocky terrain. Avalanches were also triggered naturally and by explosives in steep, rocky terrain to size 2. Avalanche activity may increase with additional snow and wind on Tuesday. The danger ratings will rise.

Snowpack Summary

Last week, 100-180 cm storm snow fell, accompanied by strong south-easterly to south-westerly winds. Storm slabs and wind slabs now appear to be slowly gaining strength. Cornices are large and threaten slopes below. A persistent weakness, formed in mid-February, continues to produce hard, sudden planar results in snowpack tests. The likelihood of triggering this layer has gone down, but very large avalanches remain possible, which could be triggered by a shallower avalanche or cornice fall. The average snowpack depth at treeline is 350 cm. With the arrival of Tuesday's storm, new storm slabs and wind slabs will develop. It may take several days for the new storm snow to settle out and start to stabilize.

Problems

Storm Slabs

An icon showing Storm Slabs
New storm slabs will build on Tuesday. Initially they may have a poor bond to last weeks storm snow which is deep and variable, and may not have fully settled.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely - Certain

Expected Size

1 - 6

Wind Slabs

An icon showing Wind Slabs
Wind slabs lurk below ridges, behind terrain features and in gullies. They may be buried by new snow, making them hard to spot. Large cornices have formed, and threaten slopes below.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 6

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
Persistent weaknesses still have the potential to create very large, destructive avalanches if triggered. Possible triggering mechanisms include a person/sled on a thin snowpack spot, cornice fall, or step-down avalanche.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

4 - 8

Valid until: Mar 20th, 2012 9:00AM