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Avalanche Forecast

Archived

Dec 20th, 2020–Dec 21st, 2020

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

Regions

Banff Yoho Kootenay.

Winds are expected to taper off moving into Monday, but the wind slabs will still be there waiting for you.

Good skiing found in sheltered areas.

Weather Forecast

Another 2-5cm of snow by Monday morning with an additional 5-15cm by Tuesday morning. Winds will drop off drastically and switch to the East as temps will range from -4 in the valley to -15 at ridge top.

Snowpack Summary

20cm of snow in the past 24hrs brings the storm total to 30-60cm. Winds slabs forming in the alpine down into tree line from strong West winds. The Dec 13 and Dec 7 sun crust/surface hoar/facet layers are down ~ 35cm and ~65cm respectively. The decomposing Nov crust/facets sits at the bottom of the snowpack. Height of snow at tree line is 80-150cm.

Avalanche Summary

A widespread natural cycle across the region today with avalanches up to sz 2.5, most notably Bourgeau Left Hand, dusting valley bottom for the second day in a row. Local ski areas were ski cutting wind slabs up to sz 1.5 and had explosive results up to sz 2.

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.