Avalanche Forecast
Issued: Dec 23rd, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind 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
Strong to extreme southwest wind forecast with light to moderate amounts of snow.
Wednesday Night: Snow 10-20 cm. Alpine temperatures -3 and freezing levels 600 m. Ridgetop wind strong to extreme from the southwest.
Thursday: Snow 5-10 cm. Alpine temperatures -4 with freezing levels 700 m. Ridgetop wind strong from the southwest.
Friday: Mix of sun and cloud. Alpine temperatures -6 and freezing levels 600 m. Ridgetop wind generally light with strong easterly gusts.
Saturday: Mix of sun and cloud. Alpine temperatures near -8 and freezing levels valley bottom. Ridgetop winds will be light.
Avalanche Summary
No new reports on Wednesday.
A 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.
Please consider sharing your observations to the Mountain Information Network. Thank you to those that have already submitted this winter!
Snowpack Summary
Recent winds have scoured some areas and combined with light amounts of new snow have built stiff wind slabs in others. Locations that have not been stripped by the wind likely have 30-50 cm of snow above 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 produces 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. This MIN report from December 22 highlights a deep release avalanche and the variable snowpack depths.
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
Wind Slabs
Storm slabs have been reactive to human triggering, especially in areas where the wind has stiffened the slab. Due to strong wind on Thursday 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 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 24th, 2020 4:00PM
