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Avalanche Forecast

Nov 28th, 2011–Nov 29th, 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
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: Purcells.

Confidence

Fair - Due to limited field observations

Weather Forecast

Light to moderate precipitation is expected over the region this evening accompanied by moderate northwesterly winds. Freezing levels will remain at valley bottom tonight through the later part of the week. Tuesday through Wednesday morning light-moderate snowfall amounts are forecast with winds continued from the northwest. Wednesday looks to become dry as a ridge moves over the Interior.

Avalanche Summary

In the Dogtooth range isolated natural avalanche activity was observed. These avalanches occurred from steep, rocky terrain at days end Sunday, up to size 1.5 due to rapid loading. I suspect this may have been the norm through the region as the freezing level was at 1800 meters and a surge of new snow and wind hammered through. This may be a good time to wait out the storm, let the new snow and the snowpack settle, and make observations from your local s mountains when the visibility improves.

Snowpack Summary

There is a lot of variation in the snowpack in this region. There is more snow in the Dogtooth area near Golden than there is further south near Invermere and Kimberley. There is probably quite a bit of snow to the west, in areas like the Bugaboos and Jumbo. We don't have any information yet from operators in the west of this region. In the early season we get most of our information from the Dogtooth. We know that there is a weak facetted layer at the ground that has been failing in the last week and resulting in very large avalanches. There has been 60-80 cms recently with strong winds and high freezing levels, creating a cohesive slab above the weak basal layer. In the higher alpine terrain there may be a rain crust from October. Areas in the region have received up to 35cm of new snow over the past 24hr period with switching winds from the northwest. This will create new storm snow and wind slab problems. Any deeper weak layers may continue to be a problem.

Avalanche Problems

Storm Slabs

Recent storm snow has created a storm slab that is likely to be triggered by backcountry riders. Avalanches started in the storm snow may step down to the weak layers near the ground.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 4

Wind Slabs

Changing winds have created new wind slabs in the alpine and at treeline on all aspects. Wind-slabs may cause avalanches to step down to the weak layer near the ground.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 4

Persistent Slabs

Where it still exists, weak basal layers in the snowpack are suspect to fail under stress of the strong slab above. It is capable producing large full depth avalanches. Large avalanches may continue to be a concern for human triggers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 5