Avalanche Forecast
Issued: Dec 3rd, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
Shifting winds may form fresh wind slabs on new aspects. Be alert to conditions that change with elevation as you get above the trees.
Summary
Confidence
Moderate - Uncertainty is due to the limited number of field observations.
Weather Forecast
Friday night: Increasing cloud. Light variable winds. Freezing level valley bottom.
Saturday: Flurries, up to 5 cm. Moderate southwest winds shifting northwest. Treeline high temperatures around -9.
Sunday: Mainly sunny. Light northwest winds. Treeline high temperatures around -12.
Monday: Mainly sunny. Light northwest winds. Treeline high temperatures around -12.
Avalanche Summary
Wind slab was reactive to explosives in the Hurley on Thursday. Reports from explosive control work in the Duffey Lake area Wednesday showed debris from releases up to size 2 (large) scouring to ground in tracks and reaching quite low in runouts. This followed the widespread natural avalanche cycle up to size 3.5 (very large) that occurred over Tuesday night. These sizes suggest that some avalanches may have involved persistent layers discussed in the snowpack summary.
Snowpack Summary
A windy conclusion to last week's storm has likely left wind slabs perched in leeward terrain features in the alpine and upper treeline. Wind slabs may see some redistribution Saturday as winds shift northwest. Below 2100 meters, this wind affected snow overlies a moist upper snowpack which is likely solidifying and bonding in the cold temperatures. Rain-wetted surfaces below 1800 m have refrozen into a thick, supportive crust that should effectively lock the snowpack in place at lower elevations.
A couple of buried weak layers produced large avalanches during a previous storm. Snowpack models indicate that these layers have been reset by recent rain at treeline, but uncertainty remains around their status in the alpine. These include a layer of surface hoar down an estimated 90-120 cm and deeper crust/facet combo layer.
Average snowpack depths in the alpine are now likely closer to 150-200 cm. Below treeline, depths of 30-50 cm have been reported around 500 m, decreasing dramatically with elevation, and still below threshold for avalanches in many areas. Early season hazards such as rocks, stumps, and creeks are still a concern below the alpine.
Terrain and Travel
- Be alert to conditions that change with elevation and wind exposure.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
Problems
Wind Slabs
As upper level winds shift northwest Saturday, any available soft snow in the alpine may be reverse-loaded into new features. Human triggering potential exists for these new wind slabs as well as older wind slabs from previous westerly winds.
Aspects: North, North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A buried weak layer may exist at upper elevations. Large loads such as wind slab releases have potential to trigger this layer to produce very large, destructive avalanches.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Dec 4th, 2021 4:00PM
