Avalanche Forecast
Issued: Dec 24th, 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
Heads up! Winds are changing from the southwest to southeast which means fresh and reactive wind slabs may be found on all aspects at upper elevations. Wind slabs may step-down to deeper persistent weak layers and produce a large avalanche. Dig down and test those layers.
Summary
Confidence
Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack.
Weather Forecast
A few flurries for Christmas as the low moves off and a bit of sunshine brings in the afternoon.
Friday: Mix of sun and cloud with isolated flurries 3-5 cm. Alpine temperatures near -4 and freezing levels valley bottom. Ridgetop wind moderate with strong gusts as its switching from southwest to southeast.Â
Saturday/Sunday: Unsettled conditions and cloudy with some flurries. Alpine temperatures near -7 and freezing levels 500 m. Ridgetop wind strong from the southeast.Â
Avalanche Summary
No new reports on Thursday.
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.
Last 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.Â
Please consider sharing your observations to the Mountain Information Network. Thank you to those that have already submitted this winter!
Snowpack Summary
Recent winds and up to 10 cm of new snow have scoured some areas 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 has been reactive to human triggering in the last week and produces size 2 avalanches.
A crust that was buried in early November sits 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
- 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
Wind slabs may be reactive to human triggering, especially in areas where the wind has stiffened the slab. Wind slabs may be found on all aspects at upper elevations on Friday as the wind direction changes from southwest to southeast. Large and possibly fragile cornices may exist on alpine ridglines.
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 in the last week.
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 25th, 2020 4:00PM
