Avalanche Forecast
Issued: Dec 4th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet, Persistent Slabs and Wind Slabs.
astclair,
Avalanche Canada
Temperatures will be on the rise through Saturday afternoon. Avoid consequential terrain and overhead hazard at peak warming.
Summary
Confidence
Low - Uncertainties in both the snowpack structure and the weather forecast limit our confidence. Uncertainty is due to the limited number of field observations.
Weather Forecast
Friday night: Mostly cloudy, 5-10 cm of snow above 1500 m, moderate southwest wind with strong gusts, freezing level rising to 1600 m
Saturday: Mostly cloudy, up to 5 cm of snow above 1600 m, moderate southwest wind, freezing level rising to 1600 m and then falling to 1400 m.
Sunday: Mix of sun and cloud, 5-10 cm of snow above 1400 m, moderate southwest winds, freezing level dropping to 1200 m.
Monday: Partly cloudy, 5-10 cm of snow above 1200 m, light south winds, freezing level dropping to 800 m.
Avalanche Summary
Avalanche observations are limited. If you're out in the field, please consider sharing a photo or description via the Mountain Information Network (MIN).
On Wednesday, a series of notable avalanches were reported in the northern half of the region. These were explosive-triggered and natural releases that resulted in very large deep persistent slab avalanches (size 3-3.5), failing on weak snow near the ground.Â
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Snowpack Summary
Isolated flurries, moderate southwest winds, and fluctuating temperatures are forecast for Saturday. Look for signs of warming and back off consequential terrain if the surface becomes moist or wet with rising temperatures.
Below a well-settled mid-pack, the bottom half of the snowpack reportedly consists of weak snow interrupted by a crust from early November. Further north in the region, we're learning that weak snow developing near the ground has produced very large deep persistent slab avalanches. Although we lack data on the distribution of this problem, the bottom line is that smaller avalanches have the potential to step-down to deeper layers and to produce large, destructive avalanches.
Snowpack depths are variable across the region, ranging from 60 cm in eastern parts of the region up to over 100 cm in western parts of the region. Lower elevation terrain may still be below the threshold for avalanches.Â
Terrain and Travel
- Back off slopes as the surface becomes moist or wet with rising temperatures.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
Problems
Loose Wet
Above freezing temperatures may trigger loose wet avalanches. Pinwheeling and rollerballs are good indicators of this type of instability. Avoid steep slopes with saturated snow, as wet loose avalanches can be surprisingly destructive due to their higher density.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Persistent Slabs
Very large avalanches over the past week suggest that a buried crust formed in early November and weak snow at the ground are reactive persistent and deep persistent weak layers. We have limited information about the distribution of this snowpack structure in the region. Keep in mind that small avalanches have the potential to step-down to these deeper layers, producing large, destructive avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Southwest winds have drifted snow into slabs on lee features that may be possible to trigger at upper elevations. Avoid steep, rocky, or convex features near ridge crests where triggering is possible.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 5th, 2020 4:00PM
