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Avalanche Forecast

Archived

Dec 7th, 2020–Dec 8th, 2020

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

Regions

Banff Yoho Kootenay.

A short but intense storm will run for 24-hrs overnight Monday and end by Tuesday afternoon. More snow to the west, less to the east. Could see 30-40 west of the divide with huge wind. All this snow will bond poorly to old snow surface.

Weather Forecast

A strong SW flow over the area will bring (possibly) significant snow overnight Monday and through the day on Tuesday. By Tuesday afternoon it will all be over. Expect a windy one early Tuesday (up to 120 km/hr), but these should taper through the day. Temperatures will remain moderate (0 to -8), then begin to cool as the skies clear for Wednesday.

Snowpack Summary

Welcome the Dec 8 layer, it should be a good one that we will all get to know. A mix of large surface hoar, sun crust, facets and old windslab from the clear skies will get buried overnight on Monday, pushed by strong to extreme winds. This will result in a short period of instability as the new snow will not bond well to all of these old grains.

Avalanche Summary

No avalanches reported on Monday, perhaps that least day of the long spell of stable conditions.

Confidence

Forecast snowfall amounts are uncertain on Tuesday

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.