Avalanche Forecast
Issued: Dec 1st, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Loose Wet and Persistent Slabs.
ghelgeson,
Avalanche Canada
We're going from cold and stormy to unseasonably warm and sunny in quite a hurry which is expected to de-stabilize our snowpack. Cornice failures and very large natural avalanches are possible as we head into the warm spell.
Summary
Confidence
Low - Uncertainty is due to the limited number of field observations.
Weather Forecast
Wednesday looks to be warm right up into the alpine. Temperatures return to more seasonal norms Thursday and Friday with a chance for a bit of fresh snow Saturday.
TUESDAY NIGHT: Freezing level between 2500 and 3000 m through the night, strong to extreme southwest wind, 1 to 5 cm of snow possible at ridge top with rain falling at most elevations. Â
WEDNESDAY: Mostly clear skies through the bulk of the day with cloud cover increasing after sunset, freezing level holding between 2500 and 3000 m, strong to extreme southwest wind, no precipitation expected.
THURSDAY: Broken cloud cover, freezing level between 500 and 700 m, moderate to strong southwest wind, 1 to 5 cm of snow.
FRIDAY: Broken cloud cover, freezing level at or near valley bottom, moderate to strong southwest wind, up to 5 cm of snow possible. Â
Avalanche Summary
Observations are very limited but the combination of snow and wind over the past few days has almost certainly formed wind slabs in open terrain.Â
Please submit your observations to the Mountain Information Network!
Snowpack Summary
The storm produced about 15 to 50 cm of new snow with areas in the far north of the region receiving the bulk of the precipitation. The wind effect is thought to be extensive. See this MIN from a few days ago which does a great job of showing the effect of the wind.
Heavy wind effect seems to be the theme from last week, and that is expected to continue into this week.
Snowpack depths range from 60 cm in eastern parts of the region up to over 100 cm in western parts of the region. Lower elevation terrain may still be below the threshold for avalanches. Reports suggest the bottom half of the snowpack consists of crusts, and in some cases weak snow may be developing around these crusts. This will be a layer to monitor as the season progresses.
Terrain and Travel
- Avoid all avalanche terrain during periods of intense solar radiation.
- Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
- Avoid exposure to slopes that have cornices overhead.
- Avoid freshly wind loaded terrain features.
Problems
Wind Slabs
Warming temperatures will exacerbate this problem. 15 to 50 cm of storm snow fell across the region over the last few days which has been formed into slabs by strong southwest wind. Large human triggered wind slabs remain likely. The new snow may be resting on surface hoar and facets which could set up a scenario where wind slabs remain surprisingly touchy.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
Wednesday marks the first day that the cold storm snow will feel both above freezing temperatures and direct sun. Loose wet avalanche activity is expected to be widespread.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
We have very little information about the prevalence of this crust in the region, but, the coming warm temperatures are combining with direct sunshine. This is combo that could easily lead to cornice failure and natural triggering of very large persistent slab avalanches running on the November crust.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 2nd, 2020 4:00PM
