Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
We are in the midst of a widespread avalanche cycle! Avoid all avalanche terrain.
Mt. Stephen, Mount Bosworth, and Sunshine Road avalanche closure zones are CLOSED on Thursday, Feb 29th.
Confidence
High
Avalanche Summary
Forecasters have observed continued evidence of a widespread avalanche cycle following the recent storm. This cycle is expected to continue through Thursday as we receive more snow and wind.
Avalanche control on Mt Whymper (Kootenay NP) on Tuesday produced size 2-3 avalanches with every shot. The crowns were 40-100 cm deep and the failure planes were the recent storm snow sliding on the Feb. 3rd crust and occasionally stepping down to ground.
Snowpack Summary
New wind slabs are forming on lee aspects at ridgetop. 30-60 cm of recent snow sits on top of the Feb 3rd crust/ facet layer. This crust is variable in thickness and exists up to 2500m (higher on solar aspects). In thinner eastern areas, the mid and lower snowpack are weak and facetted.
Average snowpack depths at treeline range from 80 cm in thinner eastern areas to 160 cm in thicker western areas.
Weather Summary
With the low tracking into southern Alberta and deepening slightly on Thursday, the snow will intensify over the Rockies.
Wednesday Night: Periods of snow ~15 cm. Low -6 °C in the alpine. Ridge wind southwest: 20 km/h gusting to 55 km/h. Freezing level at valley bottom.
Thursday: Flurries ~20cm new snow. High -5 °C in the alpine. Mostly light ridge wind, gusting 55km/h.
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Terrain and Travel Advice
- Avoid all avalanche terrain during periods of heavy snowfall.
- Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Avalanche Problems
Storm Slabs
Up to 40cm of new snow Wed night and Thurs will create touchy slabs which will include wind slabs, storm slabs, and dry loose avalanches. These could easily step down to deeper layers such as the Feb 3rd crust/facet layer and deeper persistent weak layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely - Certain
Expected Size: 1.5 - 2.5
Persistent Slabs
Up to 40cm of new snow Wed night and Thurs with wind will overlie 30-60 cm of recent snow from the last week has created touchy slabs. These slabs overlie the Feb. 3rd crust/facet combination. Numerous natural & skier-triggered avalanches have occurred in the last 3 days on this interface.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Certain
Expected Size: 1.5 - 3
Deep Persistent Slabs
Some of the recent avalanches are stepping down to the basal layers near the ground. This seems to be most common in thin, steep, rocky and higher elevation locations and less of a concern in thicker snowpacks with a dense mid-pack. Recent loading has made this layer more sensitive.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible - Likely
Expected Size: 2 - 3.5