Avalanche Forecast
Issued: Dec 26th, 2020 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
Watch for fresh wind slabs at upper elevations and be mindful of the potential for wind slab avalanches to step down to deeper weak layers.
If you see more than 15 cm of new snow in the Coquihalla area on Sunday morning, treat avalanche danger as CONSIDERABLE in the alpine.
Summary
Confidence
Moderate - Uncertainty is due to the limited number of field observations.
Weather Forecast
Saturday night: Up to 5 cm new snow, strong southwest wind easing to moderate, freezing level 500 m.
Sunday: Sun and cloud, light southwest wind, alpine temperature -7 C, freezing level 700 m.
Monday: Sun and cloud, light northwest wind, alpine temperature -3 C, freezing level 500 m.
Tuesday: Sunny, light northwest wind increasing to moderate southwest, alpine temperature -5 C, freezing level 300 m.
Avalanche Summary
Numerous skier triggered wind slab avalanches size 1-2 have been reported throughout the region over the last week. Typically they are being triggered on wind loaded convex terrain features at alpine and treeline elevations.
A few persistent slab avalanches have been triggered in the past week, mostly in the north of the region near the Hurley, but also near Allison Pass. They were triggered by riders, heavy machinery, and naturally. The slabs were generally 60 to 90 cm deep, around 2000 m, and released on the weak layers described in the snowpack summary.
Snowpack Summary
5-10 cm of new snow has been redistributed by strong overnight wind. Below treeline, the recent snow may be sitting over surface hoar.
A hard melt-freeze crust from early December is found around 40 to 120 cm deep in the snowpack. This crust may have weak layers above it, consisting of feathery surface hoar or sugary faceted grains. These weak layers are most prevalent in the north (e.g., Duffey Lake, Hurley) and found to a lesser extent in the south of the region. The snowpack should be treated as suspect anywhere you find either surface hoar or faceted grains above the crust.
The remainder of the snowpack is well-settled in the south of the region. In the north, another melt-freeze crust with associated faceted grains around it may be found near the ground. Without evidence of recent avalanche activity, the layer appears to be dormant at this time.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
Problems
Wind Slabs
Small inputs of new snow with wind overnight have likely formed fresh and reactive wind slabs. Older wind slabs have been reactive especially to skier traffic, on a variety of aspects due to variable wind direction.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Weak layers of surface hoar and/or faceted grains may be found above a hard melt-freeze crust. Recent reports suggest the weak layers may be less prevalent in the south of the region, but still exist in localized pockets.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 27th, 2020 4:00PM
