Avalanche Forecast
Issued: Dec 21st, 2020 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
The incoming storm will likely cause a widespread avalanche cycle overnight Monday and into Tuesday. This is good time to stick to non-avalanche terrain free from overhead hazards. Avalanche paths may run into below treeline terrain.
Summary
Confidence
Weather Forecast
An intense Pacific frontal system will track across BC today bringing the region strong to extreme winds and heavy snowfall amounts. High pressure will start to set up Tuesday afternoon and we can expect a clearing trend.
Overnight Monday: Heavy snow 20-30 cm. Alpine temperatures near -6 with a brief above freezing layer 1300-1500 m. Ridgetop winds strong to extreme from the southwest.
Tuesday: A mix of sun and cloud. Alpine temperature near -7 and freezing levels at the valley bottom. Ridgetop winds generally light with strong gusts from the West.
Wednesday: Mix of sun and cloud. Air temperatures falling to -12 in the alpine. Ridgetop winds light from the West.
Thursday: Sunny. Alpine temperatures -6 with an alpine inversion and freezing levels in the valley bottom.
Avalanche Summary
On Monday several loose dry avalanches up to size 1 were reported. Tomorrow will likley be a different story with new snow and wind overnight. A natural widespread avalanche cycle is expected to happen overnight and/ or tomorrow.
There have also been a few accidentally skier triggered avalanches involving both storm snow and the December crust layer such as this one from the MIN.
Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter!
Snowpack Summary
By Monday morning up to 20 cm of storm snow hit the region. The big story is the next system arriving today and tonight bringing a lot of new snow by Tuesday. Large storm slabs will be reactive, especially where they sit above a weak interface. Depending on aspect and elevation 60-100 cm now sits on the early December crust. There is increasing evidence that this persistent weak layer, with facetted crystals and surface hoar crystals above and/or below it are reaching a tipping point.
Deeper in the snowpack are two hard melt-freeze crusts that formed in November that may have some weak crystals around them. There is uncertainty if and where in the region this may be a problem.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
- Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Problems
Storm Slabs
Storm slabs will likely be reactive on Tuesday producing large and widespread avalanche activity. Simple, low angle terrain away from overhead hazard is a good choice right now.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
This layer has reached a tipping point. Depending on elevation and aspect, 40-100 cm of snow currently sits above a buried crust from early December. Sugary, facets and surface hoar around the crust mean persistent slabs are likely reactive, especially to human triggers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 22nd, 2020 4:00PM
