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Archived

Avalanche Forecast

Dec 19th, 2012–Dec 20th, 2012
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
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: Northwest Inland.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Overnight Wednesday and Thursday: Light snowfall and strong southeast winds. Winds are expected to become light by Thursday.Friday: Mix of sun and cloud / Moderate to strong east winds Saturday: Mostly clear with light east windsFreezing level is expected to remain at surface for the forecast period

Avalanche Summary

No recent avalanches have been reported. On Wednesday last week, a snowmobiler triggered a hard wind slab at the Sinclair riding area. It failed on the November crust/facet layer 30 cm above the ground while side-hilling. Check out this incident report for more details. This deep crust/facet layer has been the failure plane for a number of large avalanches further to the west and was suspected to have failed at the Hankin-Evelyn area last weekend.

Snowpack Summary

Light amounts of new snow overlie older storm and windslab instabilities which are likely settling and gaining strength. Spotty surface hoar was buried in the upper snowpack, particularly in sheltered treeline areas.  Of key concern is a November facet/crust layer which can be found near the base of the snowpack. This layer, which is widespread, can be triggered from thin-spot trigger points, or with a heavy load, such as storm slabs stepping down, a cornice fall or a snowmobile track digging a trench. It has the potential for large, destructive avalanches. In general the snowpack depths, and therefore strength is highly variable due to windy conditions this season.

Avalanche Problems

Wind Slabs

Be alert for new wind slabs in the lee of ridges and ribs.
Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 3

Deep Persistent Slabs

A deeply buried facet/crust weakness exists. This layer could be triggered by large loads, such as a cornice collapse or a rider digging deeply with a spinning track in a shallow spot on a steep, slope.
Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 5