Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
Avalanche control on Mt. Stephen is planned for Thursday, December 19; all climbing routes here are closed.
Up to 20cm of storm snow, rising temps and strong SW winds have combined to produce windslab avalanches and a mini avalanche cycle that peaked on Wednesday. Watch for winds continuing to transport snow in the wake of this storm.
Confidence
Moderate
Avalanche Summary
Avalanches were reported at both ski areas (Sunshine and Lake Louise) today, mostly size 1 but several size 2 windslabs at Sunshine, both natural and explosive triggered. Loose snow avalanches were reported on Mt Stephen, running through steep terrain and over the ice climbs.
Snowpack Summary
10-20 cm of storm snow has fallen across the region over the past 36 hours, accompanied by rising temperatures and strong winds - this is the recipe for windslab formation in many open areas. This additional weight will likely overload weak layers at the base of the snowpack, resulting in larger avalanches running on the ground. Avoid all steep, windswept alpine terrain for the next 24 hours as the storm snow settles.
Weather Summary
Wednesday night: The storm is over, clearing overnight with isolated flurries and winds continuing moderate SW.
Thursday: There will be sun and clouds, with some overcast skies and isolated flurries. No significant accumulations are expected. The temperature will range from -5 to -10, and winds will decrease.
Terrain and Travel Advice
- Avoid freshly wind-loaded features, especially near ridge crests, rollovers, and in steep terrain.
- Avoid thin areas like rocky outcrops where you're most likely to trigger avalanches on deep weak layers.
Avalanche Problems
Wind Slabs
Strong west winds and up to 20 cm of new snow has created wind slabs in lee features at treeline and in the alpine. These wind slabs may fail below the new snow interface, or step down into the deeper facets resulting in larger avalanches.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely - Very Likely
Expected Size: 1 - 2.5
Deep Persistent Slabs
Weak facets, depth hoar and crusts near the base of the snowpack continue to produce slab avalanches down about 60-100 cm. Any areas with a stiffer slab over the mid pack facets have the potential to step down to these layers. Areas of most concern are steep, thin, wind affected spots on N/NE aspects.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1.5 - 3
Loose Dry
The combination of new snow and strong winds will result in sluffing in steep gullies and couloirs on Thursday. Limit exposure to areas with overhead hazard, even below treeline.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1.5