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Avalanche Forecast

Dec 30th, 2011–Dec 31st, 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
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 Coast.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

Saturday: Dry and cool. Expect sunshine to hit the mountains for the first time in a while. Freezing level 500m. Light north-west winds. Sunday: Moderate precipitation, with the freezing level rising from 1500m to 2000m by Sunday night, when the heaviest precipitation is forecast to fall. 10-15mm. Moderate to strong southerlies.Monday: Light-moderate precipitation, mainly in the morning. Freezing level gradually lowering.

Avalanche Summary

Several natural, explosives and human-triggered avalanches have been reported to size 3. On Thursday afternoon, a backcountry skier was carried into trees by a size 2 slab. Preliminary details are: the avalanche was on a north aspect at 1920m in the Cerise Creek, Duffey Lake area. The crown depth was 70cm and the failure plane is believed to be the December 17th facet layer. The terrain was complex, including a cross-loaded feature above a gully. The skier did not survive his injuries. An adjacent slope avalanched naturally on the same layer at size 3.

Snowpack Summary

Continued snowfall has added a further 15-30cm of snow, bringing storm snow totals to the 60-90cm range. Southerly winds have shifted snow into wind slabs on lee slopes in the alpine and at treeline.Below the recent storm snow, three weaknesses exist in the upper snowpack. A surface hoar layer formed in early December overlies facets and is down about 60cm. It is giving easy-very easy, sudden collapse results in snowpack tests.A second surface hoar layer buried around Christmas is also giving easy, sudden planar results.A crust/facet combo which exists to around treeline, buried on December 17th, adds to the complexity of the snowpack and has shown the potential to propagate widely.Persistent weaknesses seem to be more of a concern around the Duffey Lake area than in the Cascades (Coquihalla and Allison Pass).The mid and lower snowpack are generally well-settled and strong.

Avalanche Problems

Storm Slabs

Weaknesses exist within or at the base of the storm snow. Forecast sunshine could trigger storm slabs on Saturday.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 5

Wind Slabs

Be alert for wind slabs in lee and cross-loaded terrain.

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 2 - 6

Persistent Slabs

Buried weaknesses in the upper snowpack have created an avalanche problem which may be triggered by people or by additional wind-loading. There is potential for surprisingly large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 2 - 6