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Avalanche Forecast

Archived

Dec 12th, 2019–Dec 13th, 2019

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

Regions

Banff Yoho Kootenay.

Watch locally for fresh wind slabs from recent winds, and don't forget there are weak facets and depth hoar at the bottom  of the snowpack that are hard to predict. Good snow quality reported in sheltered areas.

Weather Forecast

The current strong alpine winds will die right down for Friday with a slow cooling trend (lows -8 to -10) and light flurries.  The light winds and cooling trend will continue through the weekend and we will be back to -20C temperatures by Sunday. 

Snowpack Summary

Moderate to strong winds in the alpine have increased wind slab thickness. Beneath the recent 40-60 cm of storm snow, the snowpack structure is generally weak, consisting of facets and depth hoar. The Nov crust is present up to 2500m and ~30 cm up from ground. Snowpack depths at treeline range from 80-160 cm.

Avalanche Summary

Natural and explosive controlled avalanche activity has tapered form earlier this week which saw a mix of wind slabs and larger avalanches entraining the basal depth hoar and facets to size 3. Visibility was minimal on Thursday so there were no avalanche reports. 

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.