Avalanche Forecast
Issued: Dec 23rd, 2019 3:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Storm Slabs.
cgarritty,
Avalanche Canada
An unusually weak snowpack is producing very large, very destructive avalanches in the Sea to Sky region, often with light triggers. Travel in higher elevation avalanche terrain is not recommended.
Summary
Confidence
Weather Forecast
Monday night: Mainly clear with cloud increasing. Light southwest winds.
Tuesday: Cloudy with scattered flurries bringing a trace to 5 cm of new snow., continuing overnight. Light to moderate southwest winds. Alpine high temperatures around -7.
Wednesday: Becoming sunny. Light northeast winds. Alpine high temperatures around -6.
Thursday: A mix of sun and cloud with cloud increasing. Light southwest winds becoming strong at ridgetop. Alpine high temperatures around -7.
Avalanche Summary
Many large to very large persistent slab avalanches were triggered by explosives and skiers on Saturday and Sunday. The avalanches failed on the mid-November weak layer described in our Snowpack Summary. Some of the avalanches were remotely triggered, meaning the weak layer was triggered from one spot and propagated through the snowpack to reach the steeper terrain where the avalanche released. See here for some photos of one of them.
Human-triggering of large avalanches remains likely at higher elevations. We recommend avoidance of alpine and treeline avalanche terrain, given this weak snowpack.
Snowpack Summary
The upper snowpack now consists of around 70 to 120 cm of recent snow. This fell at the end of last week with very strong southwest winds.
All this snow overlies a weak layer of surface hoar as well as a deeper weak layer of sugary faceted grains and a hard melt-freeze crust buried in mid-November. This unstable structure has been producing large and destructive avalanches with light triggers over the past few days. The above mentioned 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 snowpack 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 and the consequences for triggering it are severe. The current snowpack structure is atypical for the region. It will require diligent travel practices, conservative decision-making, and some terrain avoidance until the weak layer strengthens. At the moment, expert-level terrain selection is needed, as there are many areas where you could trigger very large, very destructive avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
Thick storm slabs formed during the latest storm overlie a weak layer of surface hoar in some areas and remain reactive to the weight of a person or machine. Recent storm slab avalanches have been observed stepping down to an even deeper buried weak layer. These have resulted in destructive avalanches that travel far.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 24th, 2019 5:00PM
