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Avalanche Forecast

Archived

Dec 8th, 2020–Dec 9th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Banff Yoho Kootenay.

Storm day today with a wide range across the region; west and north of Lake Louise received twice as much snow as the Sunshine and Kootenay area. Limited observations today, but conditions are tricky for a few days so be super careful.

Weather Forecast

A strong SW flow over continues over the area, although the bulk of the moisture has passed. Expect another 5-10 cm by mid day Wednesday, then a clearing trend and wind following the storm.  Temperatures will fall and perhaps even reach -20 by Thursday.

Snowpack Summary

15-30 cm of wet snow has been deposited on top of the Dec 8 layer of surface hoar, sun crust and facets and produces easy test results at the storm snow interface. This indicates a poor bond with the new snow. Over the next 24-hours this snow will settle into a more cohesive slab and the bond will not improve due to the weak layer.

Avalanche Summary

No observations above treeline today, but many sluffs observed coming down out of the fog. Low elevations to the west also had widespread, small slabs approximately 15-20 cm deep by 2-3 m wide. Watch out on gully walls ice climbers.

Confidence

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.