Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
While the avalanche hazard is slowly dropping, human triggering remains possible. The primary concern is the threat of superficial slabs stepping down to the deep persistent weakness which could result in full-depth avalanches.
Confidence
Moderate
Avalanche Summary
Ski hill reported continued wind slab and cornice development. Explosive control triggered wind slabs up to size one. Sunshine reported one deep persistent explosive triggered avalanche in Delirium.
On Monday a large cornice failure on Ptarmigan Peak (SE aspect) triggered a 250 m wide windslab that scoured down into the basal facets. (See photo)
A skier triggered deep-persistent avalanche was reported from a shallow west facing aspect above Sherbrook Lake on Monday.
Snowpack Summary
15-20 cm of storm snow from the past week, combined with strong W/SW winds, has formed wind slabs in alpine lee areas which extend down into treeline.
The mid and lower snowpack is faceted and weak, with facet/crust interfaces near the ground. This is more pronounced east of the divide, while western regions display a deeper more settled snowpack.
Snowpack depths at tree-line are about 60 cm in eastern areas and 100 cm west of the divide.
Weather Summary
The forecast is for a mix of sun and cloud on Christmas Day followed by light flurries along the Continental Divide on Boxing Day. Ridgetop winds will be from the west/southwest in the moderate range with stronger gusts. Day-time high temperatures at treeline forecasted to be around -8.
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
Moderate to strong S and SW winds have built wind slabs in lee features in the alpine and down into treeline. Wind-loading is expected to continue through Wednesday. These slabs are a particular concern where they sit over weak facets which could result in step-downs to the basal layers.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2
Deep Persistent Slabs
Weak facets and depth hoar associated with crusts near the base of the snowpack continue to produce slab avalanches 60-100 cm deep. Any area with a stiffer slab over facetted lower packs has the potential to generate a larger avalanche that steps down ground.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1.5 - 3