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Archived

Avalanche Forecast

Dec 20th, 2011–Dec 21st, 2011
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: South Rockies.

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Wednesday: Flurries in the morning with moderate northerly winds. Alpine temperatures around -12C. Thursday: Dry. Winds becoming westerly. Remaining cold, but an inversion could locally elevate alpine temperatures by a few degrees. Friday: Flurries. Moderate NW winds. Alpine temperatures around -10C.

Avalanche Summary

We have had reports of shallow slab avalanches affecting the top 20 cm of the snowpack, running on the mid-December surface hoar layer. Although these shallow slides (to size 1.5) do not have much mass, they were reported as running "fast and far". They were reported from the Harvey Pass area at 1800-2000m on a north aspect.

Snowpack Summary

Recent strong winds have flipped from southerly to northerly and back to southerly. As a result, a highly variable snowpack exists in the alpine and exposed areas at treeline. Some areas are completely scoured; some have fresh layers of hard wind slabs. In more sheltered locations, a buried layer of surface hoar lies approximately 20 cm below the snow surface. A well settled mid pack bridges over the basal weaknesses at the ground. The crust/facet combo still exists at the ground. This layer was responsible for some large releases earlier on in the season. However, there hasn't been any activity on this layer since early December and confidence is growing that it has gained strength.

Avalanche Problems

Wind Slabs

Shifting winds have set up variable wind slabs on a variety of aspects, particularly north through southeast. Watch also for cross-loading on exposed open slopes generally oriented parallel to the wind.

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3