Avalanche Forecast
Issued: Dec 21st, 2019 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Storm Slabs.
mconlan,
Avalanche Canada
Clear skies may lure you into bigger terrain, but this is not the time to expose yourself. In many areas, the recent snow is resting on a weak layer ready to fail with the weight of a skier. Best to avoid alpine avalanche terrain and travel very conservatively at treeline.
Summary
Confidence
Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.
Weather Forecast
SATURDAY NIGHT: Mostly cloudy with isolated flurries, accumulation 1 to 3 cm, light to moderate southwest wind, alpine temperature -7 C, freezing level 1000 m.
SUNDAY: Mostly clear skies, light east wind, alpine temperature -6 C, freezing level 1000 m.
MONDAY: Clear skies, light southwest wind, alpine temperature -7 C, freezing level below valley bottom.
TUESDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate south wind, alpine temperature -8 C, freezing level below valley bottom.
Avalanche Summary
Many large slab avalanches were triggered naturally and by explosives on Friday and Saturday. The avalanches failed both in the recent storm snow as well as the mid-November weak layer described in the Snowpack Summary. Some of the avalanches were remotely triggered, meaning they were triggered from a shallow spot and traveled far through the snowpack to steeper terrain.
Human-triggered avalanches are expected to be very likely to occur on Sunday, with the potential to fail in both the recent storm snow as well as the mid-November weak layer. We recommend avoidance of alpine avalanche terrain and very conservative decision-making at treeline, given this weak snowpack.
Snowpack Summary
Around 70 to 120 cm of recent snow fell with very strong southwest wind. All of this snow overlies a weak layer of surface hoar as well as sugary faceted grains and hard melt-freeze crust buried mid-November, which is a recipe for large and destructive avalanches. These weak layers may be found anywhere from about 80 to 150 cm deep.
This weak and touchy snowpack is highly atypical for the region and may persist for some time. Conservative terrain travel along with periods of avoidance of avalanche terrain will be imperative to manage your risk until the weak snow gains strength.
Terrain and Travel
- Travel in alpine terrain is not recommended.
- Don't let the desire for deep powder pull you into high consequence terrain.
- Persistent slabs have potential to pull back to lower angle terrain.
- Make conservative terrain choices and avoid overhead hazard.
Problems
Persistent Slabs
A touchy weak layer is buried in the lower half of the snowpack. This layer has been responsible for many large avalanches in the region over the past two weeks. The consequence of triggering this layer would be severe. This snowpack setup is atypical for the region, which will require diligent terrain travel, conservative decision-making, and periods of avoidance until the weak layer strengthens. At the moment, expert-level terrain selection is needed, as there are many areas where you could trigger large, destructive avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
Storm slabs formed during this latest storm are likely to remain touchy to human traffic. Storm slab avalanches may step down to a buried weak layer, forming destructive avalanches that could travel far.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 22nd, 2019 5:00PM
