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Avalanche Forecast

Dec 20th, 2011–Dec 21st, 2011
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Purcells.

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Wednesday: Mostly dry. Light northerly winds. Alpine temperatures around -12C. Thursday: Dry. Winds becoming westerly. Remaining cold, but a mild inversion could locally elevate alpine temperatures by a few degrees. Friday: light snowfall with around 2 cm expected. Moderate NW winds. Alpine temperatures around -12C.

Avalanche Summary

A natural avalanche cycle up to size 2 occurred in the Dogtooth and Bugaboo ranges last weekend. Human-triggered slab avalanches have been reported subsequently from these areas up to size 2 on a variety of aspects and elevations. Due to the well-developed nature of the surface hoar layer, touchy avalanche conditions will persist where the slab is sufficiently deep and avalanches have not already run.

Snowpack Summary

The Purcell region has been getting less snow in the recent storms than the Selkirks. This means in many areas we have not reached critical threshold on a layer of large surface hoar and near surface facets that was buried mid-December. Exceptions to this are the Dogtooth range and Bugaboos, where avalanches to size 2 have been releasing on this layer with fracture depths of 20-30 cm. Typically, the mid-December surface hoar layer currently lies about 20 cm below the snow surface. Some areas have a sun crust in the alpine on steep south and west aspects. There is a rain crust that is buried between 40 to 55 cm in some areas that reaches up to about 2200 m. Lower in the snowpack, the mid-layers are well-consolidated and strong. Near the base of the snowpack there are a few layers that have the potential to wake up with a really big storm or very heavy loads. These include a surface hoar layer from early November, a crust/facet combo from October and the interface on steep glaciated terrain with snow that did not melt over the summer.

Avalanche Problems

Persistent Slabs

Slab avalanches are now occurring on the mid-Dec surface hoar interface in northern parts of this region.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 4

Wind Slabs

Wind slabs are sliding easily on the recently buried surface hoar. Shifting winds have set up this problem on a variety of aspects, particularly north through south east.

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3