Avalanche Forecast
Issued: Dec 21st, 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
Another winter storm with strong winds and heavy snowfall will build fresh and reactive storm slabs through the forecast period.
Summary
Confidence
Weather Forecast
Expect some enhanced snowfall amounts Wednesday through Thursday as a warm and wet air mass rises from the South and collides with a predominantly colder air mass sliding down from the North.
Tuesday Night: New snow up to 10 cm accompanied by moderate ridgetop wind from the SW. Alpine temperatures near -8 and freezing levels at the valley bottom.
Wednesday: New snow throughout the day, heavy at times with 10-25 cm of accumulation. Strong to extreme ridgetop wind and alpine temperatures near -8. Freezing levels 1000 m.
Thursday: New snow 10-25 cm accompanied by strong SW winds. Alpine temperatures near -5 and freezing levels steady at 1000 m.
Friday: Mostly cloudy with 10 cm of new snow. Gusty ridgetop winds from the South and freezing levels dropping back to the valley bottom.
Avalanche Summary
On Monday, several natural wind slabs and dry loose avalanches were seen up to size 2.
With another winter storm on the horizon, natural 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 from last weekend's storm and existing surface hoar that has been reported throughout the Kootenay Pass and Nelson area.
Below the new snow 50 to 80 cm of a well-consolidated upper snowpack overlies a substantial crust that formed in early December. This crust is approximately 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. This problem is particularly hard to predict and tricky to manage. For this reason, wide, conservative terrain margins and disciplined backcountry travel techniques will be very important. Get more details and photos in our forecaster blog.
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.
- Watch for fresh storm slabs building throughout the day.
Problems
Storm Slabs
Reactive storm slabs will build through the day with new storm snow and strong southwest wind.
In the Whitewater area, 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 50-120 cm over a crust that formed in early December. This layer has shown reactivity in snowpack tests. Avoid likely trigger spots such as steep, convex slopes, with a shallow or thick to thin snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 22nd, 2021 4:00PM
