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Avalanche Forecast

Mar 19th, 2012–Mar 20th, 2012
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Sea To Sky.

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

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.

Avalanche Problems

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

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

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