Avalanche Forecast
Issued: Dec 22nd, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Persistent Slabs and Deep Persistent Slabs.
swerner,
Avalanche Canada
New snow and strong wind on the way. Storm slabs will likely remain reactive to human triggering. Its a good time to dig down and test weak layers, especially with an active persistent slab avalanche problem. Be conservative with your terrain selection.
Summary
Confidence
Weather Forecast
Light to moderate snow and strong wind will arrive with the forecast strong Pacific frontal system.
Wednesday: Snow 5-10 cm accumulating through the day. Alpine temperatures near -3 and freezing levels valley bottom. Ridgetop wind strong from the South.
Thursday: Snow 10-20 cm. Alpine temperatures -3 and freezing levels 900 m. Ridgetop wind switching to the southeast.
Friday: Cloudy with isolated flurries. Alpine temperatures near -5 and freezing levels 600 m. Ridgetop wind moderate from the southeast.
Avalanche Summary
A new MIN report submitted on Tuesday showed a deep release from a leeward high alpine feature. The deep persistent slab problem may be isolated, however; a high consequence exists if you find yourself involved in an avalanche of this size.
On Sunday a human triggered slab avalanche size 2 was reported which started as a wind slab or storm slab and then stepped down to the early December persistent weak interface. The person was caught and partially buried. Reports from Saturday continued to highlight the instability of slabs that have formed above the early December rain crust. Check out this notable step-down release from the Hankin-Evelyn area.
Please consider sharing your observations to the Mountain Information Network. Thank you to those that have already submitted this winter!
Snowpack Summary
Incremental loading of new snow has given us 30-50 cm of recent snow. This was redistributed by recent southwest winds in exposed areas but likely remains lower density in more sheltered areas.
This recent snow sits on an early-December melt-freeze crust with weak and sugary faceted grains around it. This layer has featured in several avalanche reports that can be found on the MIN. This interface is currently reactive to human triggering and producing size 2 avalanches.
A crust that was buried in early November is near the base of the snowpack. This crust has weak facets associated with it. These facets have produced large avalanches in both the south and north of the region. Friday's reports of whumpfs suggest this layer should still play a role in guiding your terrain selection.
Snowpack depths vary substantially with aspect, elevation, and wind exposure.
Terrain and Travel
- In times of uncertainty conservative terrain choices are our best defense.
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Problems
Storm Slabs
Storm slabs have been reactive to human triggering, especially in areas where the wind has stiffened the slab. This may present as a wind slab issue in specific terrain at higher elevations, but sheltered lower elevations aren't exempt.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A 20-50 cm thick persistent slab sits above the early December crust. Around this crust are facets and potentially surface hoar in sheltered areas. Human-triggered avalanches and storm slabs have recently stepped-down to this layer producing size 2 avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
Basal facets have the potential of forming large and destructive avalanches. The most likely place to trigger this layer would be on shallow and rocky slopes. Smaller avalanches may also have the potential of stepping down to this layer.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 23rd, 2020 4:00PM
