Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
Lots of uncertainy about how much snow will fall with this storm, but with strong winds and new snow the avalanche hazard will rise on Wednesday.
If snowfall amounts are higher than forecast the danger may increase to HIGH in some areas. Monitor snowfall amounts closely and choose more conservative terrain if needed.
Confidence
Moderate
Avalanche Summary
We expect an increase in avalanche activity on Wednesday with new snow and strong west winds.
On Sunday, we received two separate reports (Report 1/Report 2) of large, human-triggered avalanches in the Highway 93N backcountry. Both avalanches involved a stiffer slab failing on the deep persistent facets/depth hoar on N/NE aspects. Recent natural avalanche activity on this layer has been minimal, but it remains active and continues to be the primary avalanche concern.
Snowpack Summary
Increasing west winds and new snow will create wind slabs in lee areas at treeline and in the alpine. This new snow will sit over a weak faceted midpack, with very weak basal facets/crusts near the ground. Western areas of the forecast region have similar layers but a slightly deeper, denser snowpack with fewer facets. Snowpack depths at tree-line are 40-60 cm in eastern areas and 100 cm west of the divide.
Weather Summary
Tuesday night: Snow begining in the evening with 5 cm expected overnight accompanied by strong west winds.
Wednesday: Snow continuing with an additional 5-10 cm expected throughout the day. Strong west winds continue through the day. Treeline temperatures remain steady near -7°C.
Note: Local snowfall amounts may be higher than expected with this storm.
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 new snow will create 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
Expected Size: 1 - 1.5
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 - 2.5
Loose Dry
The combination of new snow and strong winds will result in sluffing in steep gullies and couloirs on Wednesday. Limit exposure to areas with overhead hazard while the storm is occurring.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood: Likely
Expected Size: 1 - 1.5