Avalanche Bulletin - Sea to Sky
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.
|Tue, 24 Dec||Wed, 25 Dec||Thu, 26 Dec|
|Alpine||4 High||3 Considerable||3 Considerable|
|Treeline||4 High||3 Considerable||3 Considerable|
|Below Treeline||1 Low||1 Low||1 Low|
Travel and Terrain Advice
- 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.
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.
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.
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.