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: 5- 10 cm of new snow accompanied by strong ridgetop wind from the southwest. Alpine temperatures near -5 and freezing levels 900 m.
Thursday: New snow throughout the day, with 10-25 cm accumulation. Strong ridgetop wind from the southwest. Alpine temperatures near -2 and freezing levels 1100 m.
Friday: Flurries with new snow 5-10 cm with moderate to strong southwest wind. Alpine 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 Wednesday, the South Rockies field team reported several wind slabs that appeared to have slid on the early December crust and up to size 2.
With the new snow and strong wind, fresh and reactive storm and wind slabs will be reactive 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 in exposed areas, strong to extreme winds may strip many areas back down to the early December curst and create deposits of hard wind slab in lees.
Below the new snow exists a well-consolidated upper snowpack which overlies a substantial crust that formed in early December. This crust is approximately 50-90 cm below the surface, 20 cm thick on average, and is present across all aspects to at least 2400 m. A layer of weak facets (sugary snow) has been reported above this crust. Snowpack tests are generally showing hard results on this interface, however, areas, where avalanches have recently failed on this crust, continue to be problematic once reloaded with new snow.
Below 2300 m, several early-season crusts make up the lower snowpack. Snowpack depths range from 80-150 cm at treeline elevations and taper quickly below 1900m.
Terrain and Travel
- Watch for fresh storm slabs building throughout the day.
- 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 a persistent slab.
Problems
Storm Slabs
Reactive storm slabs will build with warmer temperatures, new snow, and wind loading. Leeward wind-loaded slopes may host thicker and stiffer slabs.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A layer of weak facets (sugary snow) can be found down 50-90 cm over a crust that formed in early December. This layer has produced large avalanches from explosive triggers and has shown 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
