Avalanche Forecast
Issued: Dec 20th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Deep Persistent Slabs.
jcoulter,
Avalanche Canada
Give the snowpack time to adjust to recent loading, especially in open areas where snow may have been wind stiffened. Use small low consequence slopes to test the bond of the recent snow to older layers.
Summary
Confidence
Moderate - Uncertainty is due to limitations in the field data.
Weather Forecast
SUNDAY NIGHT - Flurries, 5-10 cm / light southwest wind gusting to strong / alpine low temperature near -3 / freezing level down to 300 m
MONDAY - Cloudy with sunny periods and isolated flurries 0-5 cm / light to moderate north west wind / alpine high temperature near -4Â
TUESDAY - Cloudy with sunny breaks, no new precipitation / light winds / alpine high -4Â
WEDNESDAY- Flurries, moderate accumulations possible, light gusting to moderate winds, inversion possible
Avalanche Summary
On Sunday there were reports of shooting cracks in convex (roll over) type features. Avalanches up to size 2 out of steep, wind loaded features were reported on Saturday.
On Wednesday and Thursday there were many MIN reports suggesting the ever increasing storm snow amounts were reactive to human triggering.
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Snowpack Summary
Precipitation will start to ease by Monday but storm slabs may continue to reactive to human triggering especially where the snow has been stiffened by wind. Some areas have seen upwards of a meter of new snow in the past week.
A crust that was buried in early December is now down 80-120 cm in the alpine but is closer to the surface at and below treeline elevations. Around this crust are facets and potentially surface hoar in sheltered areas. Storm slabs may step down to this layer.
The early-November crust is buried around 100-200 cm at treeline. This crust may have weak and sugary facets above it in parts of the region. This layer has produced large, full-depth avalanches in the past few weeks. Uncertainty remains about where this layer remains a problem in the region, but it may be localized to the northern half of the region.
Terrain and Travel
- Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Be careful with open slopes and convex rolls, especially in more extreme terrain.
- Be careful as you transition into wind affected terrain.
Problems
Storm Slabs
On open slopes in the alpine and treeline this may present more like a windslab problem, but even in more sheltered zones the snow needs some more time to adjust to recent loads. In some areas storm slabs have been stepping down to early December crust layer.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Weak faceted grains may overly a melt-freeze crust near the base of the snowpack. There is uncertainty on where this layer remains a problem in the region, but large avalanches have recently occurred in the northern half of the region. The most likely area to trigger it would be in thin, rocky snowpack areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 21st, 2020 4:00PM
