Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
A bit of new snow overnight Saturday, with a forecast for strong winds into the start of the week will extend the possibility of natural avalanches.
While wind slabs may seem manageable, the primary concern is the threat of superficial slabs stepping down to the deep persistent weakness to result in full-depth avalanches.
Confidence
Moderate
Avalanche Summary
The ski hills continued to trigger wind slabs with ski cuts and explosives today, ranging up to size 2, failing 10 to 40 cm deep.
Sunshine Snow Safety reported using a 1lb charge to trigger a sz 2.5-3 slab that failed up to 2m deep and 30m wide that ran 450m in W-NW alpine ridge-crest terrain. The October crust was the bed surface.
On flights and field trips we have observed failures at both the wind slab interface and the deep persistent problem since the latest storm on Dec 18.
Snowpack Summary
Up to 20 cm of storm snow fell last week. This snow, combined with strong winds, formed wind slabs throughout the alpine and into treeline.
The mid and lower snowpack is faceted and weak with the two deep persistent slab interfaces sitting near the ground. This is more pronounced east of the divide, while western regions display a deeper snowpack that is more settled.
Snowpack depths at tree-line are about 60 cm in eastern areas and closer to 100 cm west of the divide.
Weather Summary
Overnight Saturday expect up to 5 cm of snow with higher amounts closer to the divide as temperatures at treeline remain around -4C. Moderate west winds should shift northwest and diminish into Sunday. West winds are forecast to rebuild into Monday and may increase further into Tuesday.
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.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avalanche Problems
Wind Slabs
Moderate to strong south through west winds continue to build slabs in lee features in the alpine and well into treeline. Continued warm temperatures and a small pulse of snow Saturday night will promote further slab development.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
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 facets has the potential to generate an avalanche that steps down to these layers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible - Likely
Expected Size: 1.5 - 3