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Archived

Avalanche Forecast

Dec 29th, 2011–Dec 30th, 2011
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
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
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

Regions: Northwest Coastal.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertainfor the entire period

Weather Forecast

Friday: Light snowfall, perhaps 10-15cm accumulation. Moderate westerlies.Saturday: Light snow. Freezing level near surface. Moderate westerlies. Sunday: Moderate precipitation. Freezing level rising to 1400m in the afternoon.

Avalanche Summary

Highways avalanche control produced numerous Size 2-3.5 slab avalanches. The largest of these failed at ground, up to 4m deep.

Snowpack Summary

Over the past week the northwest has been slammed by snow, strong to extreme winds, and fluctuating freezing levels. The week's tally is closing in on 200cm near Terrace, with areas to the north seeing a little less (Stewart up to 120cm). New snow has been blown around by strong south to southwest winds creating wind slabs on lee slopes and scoured windward slopes.In addition to the more obvious direct-action storm instabilities, local avalanche professionals have some other concerns: Surface hoar that formed during the winter solstice sits approximately 50-70cm below the surface. As well, the crust-facet combo (extends up to alpine elevations in the south and to 1000m in the north) from the early December dry-spell sits about 160cm below the surface and has not gone away. Any avalanches on this layer would be highly destructive and are probably waiting for the right load or trigger. Add the new observations of avalanches failing at ground and we have quite a package.

Avalanche Problems

Wind Slabs

Deep wind slabs are likely in exposed lee and cross-loaded terrain in the alpine and at treeline.

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 2 - 7

Storm Slabs

Storm slabs are growing in size and likelihood and may be triggered naturally or by the weight of a person.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 6

Persistent Slabs

There is a possibility of highly destructive avalanches where the deeply buried mid-December crust/facet layer persists.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 6