Avalanche Forecast

Issued: Feb 9th, 2012 8:36AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs, Deep Persistent Slabs and Cornices.

Avalanche Canada ccampbell, Avalanche Canada

Summary

Confidence

Good - -1

Weather Forecast

A series of weak frontal systems are expected to bring light amounts of fresh snow to the region on Friday, and trace amounts for Saturday and Sunday, but the timing is uncertain. Winds are expected to be generally light southwesterlies, but winds associated with snow squalls could get quite gusty. Freezing levels should remain in valley bottoms but could rise above 1000m with the passage of warm fronts.

Avalanche Summary

Throughout the weekend numerous highly destructive persistent deep slab avalanches involving basal facets and depth hoar occurred in the alpine and ran to valley bottoms (check out the Avalanche Image Gallery under the Library tab for some photos). These highly destructive avalanches remain possible with heavy triggers, such as airborne sled impacts and cornice falls, in thin areas on variable slopes peppered with tree's and rocks.

Snowpack Summary

In Elk Valley North and the Crowsnest, the average snowpack depth at treeline is 150 cms. In Elk Valley S and the Flathead the snowpack depth is closer to 2 m. Surface hoar is continuing to develop on sheltered slopes at all elevations combined with near-surface facets at lower elevations and surface crusts on sun-exposed slopes. A well settled and strong snowpack sits on weak basal facets and depth hoar, which seem to be fairly widespread throughout the region. This deep persistent weakness recently became active again with warm temperatures, but cooler temperatures have once again reduced the sensitivity to triggers. Highly unpredictable glide cracks are also opening up, primarily on slopes with smooth ground cover. These full-depth gaping 'crevasses' could release without warning or act as a significant terrain trap.

Problems

Wind Slabs

An icon showing Wind Slabs
Fresh wind slabs are expected to develop below ridge crests and behind terrain breaks in lee and cross-loaded terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
Deep and destructive persistent slabs have become less likely, but may be triggered with a large trigger (cornice fall, trenching sled); especially in unsupported, rocky terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Cornices

An icon showing Cornices
Cornices are large, unsupported and may be a trigger for a large avalanche on the slope below.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Valid until: Feb 10th, 2012 3:00AM

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