Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
While the hills looked pretty for a few days following the storm: the SW winds returned with a vengeance bringing a natural avalanche cycle Saturday.
Avoid exposure to overhead avalanche terrain as large natural, and remotely triggered, avalanches are expected.
Freshly formed windslabs will be sensitive to human triggering.
Confidence
Moderate
Avalanche Summary
Natural avalanches to sz 2.5 were observed around Banff Saturday afternoon as huge plumes of wind transported snow streamed off of Mt Rundle and Cascade. The Urs Hole ice climb ran sz 2.5 and Bourgeau Right-hand ran twice at sz 2.
Highway avalanche control on Friday produced results to size 2.5 on Mt Bosworth. While helicopter avalanche control work at Lake Louise produced results up to sz 3, of which one was remotely triggered from 250m away.
Snowpack Summary
Last week's 60cm+ of storm snow fell on the Dec 2 weak layer (Surface Hoar, Facets, and Sun Crusts) which capped a weak snowpack featuring several weak faceted layers and a spotty crust and depth hoar layer against the ground. While there is some separation between these weaknesses in the alpine, at treeline and below they are essentially the same layer.
A rain crust exists buried 20-40 cm at lower elevations.
80-100 cm at treeline with up to 140cm observed in alpine locations.
Weather Summary
Strong to Extreme SW winds are expected to shift W and back off into the moderate to range through the day Sunday.
Small amount s of snow can be expected as temperatures warm through the overnight period bringing alpine high temperatures near -7C Sunday.
For more information, click Mountain Weather Forecast.
Terrain and Travel Advice
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Remote triggering is a concern, watch out for adjacent and overhead slopes.
- Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
Avalanche Problems
Deep Persistent Slabs
The storm snow comprises 1/2 to 3/4 of the snowpack that formed a slab over the very weak, shallow snowpack that existed before the storm.
No matter which layer of the old snow these slabs initiate on, the entire lower snowpack will likely become involved resulting in a large, destructive avalanche.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 3
Wind Slabs
While last week's storm snow arrived with very little wind, SW winds reached strong to extreme values Saturday and are expected to be remain elevated into Sunday. With lots of snow to available to transport, wind slabs are forming quickly and will be sensitive to human triggering.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2