Avalanche Forecast
Issued: Dec 22nd, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
swerner,
Avalanche Canada
New snow accompanied by strong southwest wind will lead to a widespread avalanche cycle.
Summary
Confidence
Weather Forecast
Continued snow through the Christmas holidays. Expect some heavier snowfall amounts Thursday with the passing cold front.
Wednesday Night: 10- 15 cm of new snow accompanied by strong ridgetop wind from the southwest. Treeline temperatures near -5 and freezing levels 900 m.
Thursday: New snow throughout the day, heavy at times with 15-25 cm accumulation by the afternoon. Strong ridgetop wind from the southwest. Treeline temperatures near -2 and freezing levels 1100 m.
Friday: Flurries with new snow 5-10 cm with moderate to strong southwest wind. Treeline temperatures near -5 and freezing levels valley bottom.
Saturday: Mostly cloudy with some flurries 5-10 cm. Gusty ridgetop winds from the South and temperatures dropping to -12 with freezing levels valley bottom.
Avalanche Summary
On Tuesday, several natural loose dry and wind slab avalanches up to size 2 were reported. A recent MIN report also showed a human-triggered wind slab size 1 from a North aspect. Explosive control on Northerly aspects from 1800-2000 m produced loose dry and soft slab avalanches up to size 2.
Widespread natural and human triggered storm slab avalanches will be likely through the forecast period.
Snowpack Summary
New snow and wind will likely build reactive storm slabs through Friday. This new snow will bury older wind slabs and existing surface hoar that has been reported throughout the Kootenay Pass and Nelson area.
Below the new snow exists a well-consolidated upper snowpack which overlies a substantial crust that formed in early December. This crust is approximately 70-100 cm below the surface, 10 cm thick on average, and is present across all aspects to at least 2300m. A layer of weak facets (sugary snow) has been reported above this crust.
The lower snowpack is composed of several early-season crusts. Snow depths at treeline average 150-200 cm. Below 1800 m the snowpack remains relatively shallow with 80-120 cm on average. The deepest snowpack can be found in the Kootenay Pass area.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
Problems
Storm Slabs
Reactive storm slabs will build with warmer temperatures, new snow, and wind loading.
Surface hoar has been reported below the new snow. This will make slabs more widespread and increase the reactivity and propagation potential. Be suspicious of any areas treeline and below where a slab exists, especially in sheltered areas where this surface hoar may be preserved.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A layer of weak facets (sugary snow) can be found down 60-100 cm over a crust that formed in early December. This layer has shown some reactivity in snowpack tests. The new snow may add enough stress to trigger a persistent slab.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 23rd, 2021 4:00PM
