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 recent snow has helped the ski quality, but strong alpine winds have created new wind slabs in lee areas. The primary concern is the threat of superficial slabs stepping down to the deep persistent weakness resulting in full-depth avalanches.
Confidence
Moderate
Avalanche Summary
The ski hills continue be able to trigger deep persistent slabs with explosives up to size 2, failing on the basal facets/crust. One was on a relatively low angle slope of 30-34°. They have also used explosives or ski cutting to trigger small windslabs in steep lee areas but these are becoming stubborn.
Natural avalanche activity has slowed down in the past couple days with a couple of wind triggered avalanches in steep lee alpine terrain on Sunday and no new reports on Monday.
Snowpack Summary
Thin sun crust on steep solar aspects. 15-20 cm of storm snow from the past week combined with strong W/SW winds, has formed wind slabs in alpine lee areas and 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 snowpack with fewer facets.
Snowpack depths at tree-line are about 60 cm in eastern areas and 100 cm west of the divide.
Weather Summary
SW ridgetop winds will increase by Tuesday morning and slowly drop into Wednesday. Like the events over the last weekend, this system remains relatively dry and only a few cm of snow is forecast Tuesday into Wednesday. A mix of sun and cloud on Tuesday with more cloud to the west, and treeline temperatures between -4°C and -7°C.
Terrain and Travel Advice
- Avoid freshly wind-loaded features, especially near ridge crests, rollovers, and in steep terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- 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 south through west winds have built wind slabs in lee features in the alpine and down into treeline. Strong winds will continue on Tuesday so watch for additional loading. These slabs are a particular concern where they sit over weak facets and could step down 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 the mid-pack and deep facets has the potential to generate an avalanche that steps down to the deep layers and end up being quite large.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1.5 - 3