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Avalanche Forecast

Feb 23rd, 2012–Feb 24th, 2012
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
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
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: South Columbia.

A Special Public Avalanche Warning has been issued for this region for February 24-27. Current conditions are very touchy and require extremely conservative decision making.

Confidence

Good

Weather Forecast

Friday: Moderate snow beginning in the morning - 5-15cm. The freezing level (FL) is around 500-800m. Ridge top winds should be moderate from the SW. Saturday: Continued moderate snowfall - an additional 10-20cm overnight and through the day. FL 800-1000m. Winds should ease to light from the west. Sunday: Unsettled conditions with convective flurries likely. FL drops to valley bottom. Winds are light and variable.

Avalanche Summary

A large natural avalanche cycle occurred on Wednesday. Slab avalanches were reported up to Size 3.5 on all aspects and at all elevations. There were also numerous reports of skier triggered and remotely triggered avalanches on a variety aspects. The potential for human triggered avalanches remains high in all terrain over 30 degrees.

Snowpack Summary

Moderate west-northwest winds have created weak wind slabs in exposed alpine and treeline terrain. Up to 70cm of new snow now sits on the February 16th Surface Hoar layer and is slowly settling into a cohesive slab. The February 8th weakness is now down 80-100cm. This layer is a combination of weak layers: In most locations it marks a widespread surface hoar layer. On steep south & west facing aspects a sun crust that formed during the drought was also buried on Feb. 8th. This crust likely has a bit of faceting below it too, meaning that most terrain in the region has a weak layer 40-60cm under the snow surface. These buried weaknesses have made conditions very tricky with the potential for triggering in lower angle terrain and from a distance. It is should be noted that large cornices remain widespread throughout the region and may fail as temperatures fluctuate over the next few days.

Avalanche Problems

Wind Slabs

Previous W-NW winds and forecast SW winds have created dense wind slabs in exposed lee and cross-loaded terrain at all elevations.

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

Elevations: All elevations.

Likelihood: Very Likely - Certain

Expected Size: 2 - 7

Persistent Slabs

Several buried weaknesses including surface hoar and/or a crust are ripe for triggering naturally or by the weight of a person. It may be possible to trigger avalanches in surprisingly low-angle terrain or from a distance.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Very Likely - Certain

Expected Size: 2 - 7