Avalanche Forecast

Issued: Dec 7th, 2023 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs and Deep Persistent Slabs.

SH, Avalanche Canada

Banff Yoho Kootenay, Banff, East Side 93N, Kootenay, LLSA, Lake Louise, Sunshine, West Side 93N, Field, Little Yoho.

Avalanche control Dec 8 on Mt. Bosworth and the Mt. Stephen intermittent closure zone. No activities in these areas.

Deeper weak layers are overloaded by up to 60cm of storm snow, which will take time to settle. Climbers and skiers should factor in that avalanches starting up high can extend below treeline in gully features.

Summary

Confidence

Moderate

Avalanche Summary

Numerous avalanches were reported Thursday, including widespread naturals to 2.5 at Lake Louise ski hill. Other naturals were observed in the backcountry of Yoho, but overall, there has been limited visibility.

Snowpack Summary

Up to 60 cm of storm snow overlies the Dec 2 layer of surface hoar, facets and a crust. Below this layer are basal facets and a crust formed in late October. We suspect there is some separation between these weak layers in the alpine, but at treeline and below, they are essentially the same layer. Snow depths range from 80-100 cm at treeline and up to 140cm observed in alpine locations.

Weather Summary

Thursday night: light NW winds, freezing levels to valley bottom and 2-4cm in all regions.

Friday: Temperatures start to cool. Expect clearing starting mid-day with NW winds 20-30kmh at treeline.

For more information, click Mountain Weather Forecast.

Terrain and Travel Advice

Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

Up to 60 cm of storm snow overlies a weak interface of surface hoar, facets and some sun crust from Dec 2. This weak layer is easily triggered, and the resulting avalanches often step down to the basal facets, resulting in even larger slides.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

The lower snowpack is weak with facets, depth hoar and a spotty crust from late Oct. Avalanches on this layer will either "step down" from a storm slab avalanche or initiate on the ground. These avalanches may be large enough to run below treeline.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Dec 8th, 2023 4:00PM