Avalanche Forecast
Issued: Dec 29th, 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.
cmortenson,
Avalanche Canada
Freshly formed wind slabs may form lee of ridgecrests at treeline and above. Continue to make conservative terrain choices and be extra cautious of shallow and / or rocky slopes where it is possible to trigger a deeper weak layer.
Summary
Confidence
Weather Forecast
Tuesday night: Isolated flurries, alpine low temperatures -6C, freezing levels valley bottom & ridgetop winds moderate southwest.
Wednesday: Scattered flurries, trace - 10 cm new snow, alpine high temperatures -6C, freezing levels valley bottom & ridgetop winds light southeast.
Thursday: A mix of sun and clouds, alpine high temperatures -5C, freezing levels valley bottom, ridgetop winds moderate west.
Friday: Scattered flurries wth trace - 10 cm new snow, alpine high temperatures -7C, freezing levels valley bottom, ridgetop winds strong southwest.
Avalanche Summary
Fresh wind slabs continue to produce avalanches (size 1-2) when tested with explosive and with ski-cutting. In the days following Christmas, there were numerous natural and explosive triggered large (size 2) wind slab avalanches and loose dry avalanches in steep terrain. A few large (size 2) avalanches involved the December crust.
A significant avalanche from the deep basal facets was reported in this MIN report from Dec 22nd showed a deep release from a leeward high alpine feature off the north side of Hudson Mountain. The deep persistent slab problem may be isolated, however it remains a very high consequence if you find yourself involved in an avalanche of this size.
Snowpack Summary
Isolated flurries add to recent snow fall amounts (10-30 cm) from previous days. Recent snow has buried wind affected snow in alpine and exposed tree line regions. Underneath this soft snow you may encounter scouring, buried wind slabs, cross loading or reverse loading patterns.
The December crust layer is buried 30-80 cm and featured in several avalanche reports from Dec 19th & Dec 17th. Although it appears to be gaining strength, It remains a notable weak layer. We continue to monitor it, particularly in shallow or rocky snowpacks. This MIN from the 27th found the crust down 65 cm.
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 why we continue to advise caution around shallow rocky areas in the alpine.
Snowpack depths vary substantially with aspect, elevation, and wind exposure.
Terrain and Travel
- Be alert to conditions that change with elevation, aspect and exposure to wind.
- 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 because the wind direction has changed, but predominately winds have been from the west/southwest.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A 30-80 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 stepped-down to this layer producing large 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 and continues to show up in test pits as reactive. The most likely place to trigger this layer would be on shallow and rocky slopes. Smaller avalanches or cornice collapse may also have the potential of stepping down to this layer.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 30th, 2020 4:00PM
