Avalanche Forecast
Regions: Bonnington, Crawford, Grohman, Kokanee, Kootenay Boundary, Kootenay Pass, Moyie, Norns, Retallack, Rossland, St. Mary, Valhalla, Whatshan, Ymir.
Rising temperatures and strong sun are creating very dangerous avalanche conditions. Large, destructive natural avalanches are likely. Avoid all avalanche terrain.
Confidence
High
Avalanche Summary
Widespread large natural avalanche activity was reported on Monday and Tuesday, including wet loose to size 2 and storm & persistent slabs to size 3. On Sunday, an extremely large avalanche, suspected size 4, was observed running to valley bottom and climbing up the other side.
We can expect large, destructive persistent slab avalanche activity to continue as temperatures continue to climb on Wednesday.
Snowpack Summary
A moist to wet upper snowpack snow sits over a crust. Below lies a complex snowpack with several weak layers which are currently concerns for triggering persistent slab avalanches:
Facets/surface hoar/crust from early March buried 40 to 60 cm deep,
Facets/surface hoar/crust from mid-February buried 110 to 130 cm deep, and
Facets/surface hoar/crust from late January buried 120 to 160 cm deep.
This complex snowpack combined with dramatic warming makes travel in avalanche terrain dangerous.
Weather Summary
Tuesday night
Clearing skies. 20 to 30 km/h southwest ridgetop wind. Treeline temperature +6 °C. Freezing level rising to 2800 m.
Wednesday
Sunny. 10 to 20 km/h south ridgetop wind. Treeline temperature +9 °C. Freezing level 3100 m.
Thursday
Cloudy with rain turning to snow, 5 to 10 cm. 20 to 40 km/h southwest ridgetop wind. Treeline temperature 0 °C. Freezing level falling to 2000 m.
Friday
Cloudy 5 to 15 cm of snow. 30 to 40 km/h south ridgetop wind. Treeline temperature -1 °C. Freezing level 1000 to 2000 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be aware of the potential for large, destructive avalanches due to deeply buried weak layers.
- Very large and destructive avalanches could reach valley bottom.
- Only the most simple non-avalanche terrain with no overhead hazard is appropriate at this time.
Avalanche Problems
Persistent Slabs
Several persistent weak layers exist in the upper meter of the snowpack. As temperatures continue to climb on Wednesday, these layers are expected to fail naturally, producing very large and destructive avalanches.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 2 - 3
Loose Wet
As temperatures rise, expect a heavy, wet upper snowpack to produce storm slab and loose wet avalanches, especially on sun-exposed slopes.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 2.5
Cornices
Cornices are large, looming and becoming weak with warm temperatures and sun. A large cornice fall can be dangerous on its own, and can also trigger deep slabs on slopes below.
Aspects: North, North East, East.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 1.5 - 3