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Avalanche Forecast

Archived

Nov 20th, 2012–Nov 21st, 2012

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Little Yoho.

Weather Forecast

The storm is over. Expect mixed sun and cloud with light snow accumulations through the end of the week. Temperatures will cool off slightly with freezing levels near valley bottom. Winds forecast to be light from the west.

Snowpack Summary

30 cm of storm snow at tree-line along the continental divide along with moderate to strong westerly winds has created wind-slabs in the alpine. Wind slabs are reactive to skier triggering on steep lee terrain. Easy shears at storm snow interface and mod shears down 60 cm on Nov 6 crust.

Avalanche Summary

Sunshine Ski Hill reported several class 1 avalanches ski cut within storm snow on steep rolls. During field trip to Bow Summit area no natural avalanches were observed although visibility was not great. Some whoomphing was heard at treeline.

Confidence

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.