Avalanche Forecast
Issued: Dec 18th, 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.
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Avalanche Canada
Incoming weather will increase avalanche danger to HIGH this weekend. Avoid avalanche terrain by sticking to simple terrain with low angle slopes and no exposure to overhead hazard.
Summary
Confidence
Weather Forecast
Weekend will be stormy with Monday looking dry and clear.
FRIDAY NIGHT: 10 to 20 cm overnight, highest amounts on the westerly side of the mountains. Strong southwest wind. Freezing level around 1000 - 1200 m.
SATURDAY: Break between systems so dry, cloudy with some afternoon clearing possible, continued strong southwest wind.
SUNDAY: wake up to new snow that fell overnight, around 10 to 25 cm in westerly and deeper snowpack areas. Light snow and cloudy during the day, continued moderate to strong southwest wind.
MONDAY: Clear, dry, light variable wind, and -10 C or colder temperatures.
Avalanche Summary
A natural avalanche cycle up to size 2 or 2.5 on Wednesday was reported in northern parts of the region. The key point is the weakness was surface hoar -- expect more and bigger events on this layer.
On Thursday a size 2.5 or 3 was reported in Pine Pass -- the key point is it was bigger (see previous sentence).
I expect a significant avalanche cycle this weekend, especially where surface hoar from last week exists below the recent snow.
Snowpack Summary
Upper snowpack is made up of new or recent snow and with the storm systems lined up to track through the region this storm snow will continue to build. The forecast wind will also build windslabs. In some areas in the north (Pine Pass, possibly Wolverine) there is surface hoar near the bottom of this recent snow -- which may be as deep as 50 or 60 cm.
Mid-pack is where you'll find a variety of crusts. Most reports haven't found them to be an issue.
Basal-pack, the basement also has some crusts. I suspect the layer to be potentially reactive in northern parts of the region, such as Pine Pass, but do not have observations to back this up.
Snow depths are approaching 200 cm around Pine Pass, Torpy and McBride and around 100 cm in the northeast around Tumbler Ridge.
Terrain and Travel
- Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.
- Avoid areas with overhead hazard.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Storm Slabs
With incoming snow and wind loading avalanches are on 30 degree or steeper slopes (moderate angle) where more than 30 accumulates are very likely, especially if there's surface hoar below. Wind loaded slopes are especially suspect.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
We are uncertain about where the early-November crust has weak faceted grains above it, and if this layer remains as a problem.
Our limited information suggests this problem is more likely found around Pine Pass and the eastern slopes of the Rockies. Given our lack of field observations, the prudent choice is to approach any big open slope with caution, especially slopes that are rocky and have variable snowpack depths.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 19th, 2020 4:00PM
