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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
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
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
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Glacier.

Rising winds are forcast to reach 70kph at ridge tops. This could cause rapid soft slab development. Use caution for soft wind slabs where slopes are exposed to the wind.

Weather Forecast

A large low in the gulf of Alaska is bringing cloudy and more stormy skies in from the South-West, flurries are forcast for today and tonight, and snow for Thursday. Amounts are predicted to be 2cm today, 5cm tonight, and 10 or more cm for thursday, but there is low confidence in the predicted amounts. Rising winds are forcast, SW 30 rising to S 70

Snowpack Summary

At treeline and above, soft windslabs have formed due to 30-50k winds at ridgelines. Elsewhere, 40cm of loose storm snow overlies a well settled snowpack. The Nov28 surface hoar is down about 80cm but only in some locations. The early Nov crust is widespread and down about 1.5m. Tests on these layers indicate they would be hard to trigger.

Avalanche Summary

Yesterday avalanches were observed up to size 2.5, and were dry slabs running to 1/4 fan.

Confidence

Intensity of incoming weather systems is uncertain

Avalanche Problems

Wind Slabs

Strong winds early this week, combined with 40cm of storm snow have created touchy windslabs at treeline and alpine elevations that are easily triggerable on convex, unsupported features. Look for soft slabs at or near ridgelines.
Be cautious as you transition into wind affected terrain.Watch for terrain traps where small amounts of snow will acumulate into deep deposits.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 3

Persistent Slabs

While the thick crust at the base of the snowpack has yet to be reactive, if it does produce an avalanche it will be very large. Cornice falls or other avalanches stepping down to this layer, or triggering from thin areas are possible.
Sluffs may trigger deeper instabilities.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 4