Avalanche Forecast
Issued: Dec 25th, 2019 3:00PM
The alpine rating is Persistent Slabs and Storm Slabs.
, the treeline rating is , and the below treeline rating is Known problems includeOur snowpack structure remains very concerning to avalanche professionals throughout the region. Obvious feedback (natural avalanches) may be diminishing, but our persistent slab problem remains active. Keep seeking out conservative terrain options.
Summary
Confidence
High -
Weather Forecast
Wednesday night: Clear periods. Calm or light southwest winds.
Thursday: Cloudy with light flurries developing late in the day, bringing a trace to 5 cm and continuing overnight. Light to moderate southwest winds increasing over the day and becoming strong at ridgetop. Alpine high temperatures around -8.
Friday: Cloudy with new snow totals of 10-15 cm. Light to moderate southwest winds. Alpine high temperatures around -7.
Saturday: Cloudy with scattered flurries bringing 5-10 cm of new snow, continuing overnight. Light to moderate south winds, becoming strong at ridgetop. Alpine high temperatures around -5.
Avalanche Summary
Reports from Monday and Tuesday showed more observations of the widespread large to very large (size 2-3) natural avalanches that have run recently, along with numerous (but diminishing) new explosives-triggered size 2-3 releases, targeted in the Whistler area.
Many more size 2-3 avalanches were triggered by explosives and by skiers on Saturday and Sunday.Â
Many of the avalanches mentioned above failed on the mid-November weak layer described in our Snowpack Summary. Many of the larger examples scoured the lower snowpack away to reveal ground. Some of the avalanches were remotely triggered. See here for some photos of one of them.
Human-triggering of large avalanches remains likely at higher elevations. Very cautious route-finding and conservative decision making is currently required for safe travel in higher elevation avalanche terrain.
Snowpack Summary
Large new surface hoar is beginning to be reported on the snow surface in sheltered areas. Below the surface, the upper snowpack consists of around 70 to 120 cm of snow from the storm at the end of last week.Â
All this snow overlies a weak layer of surface hoar as well as a deeper (100-200 cm) 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, often with light triggers and even remote (from a distance) triggers over the past several days.
This weak and touchy snowpack is atypical for the region and is expected to persist for some time. Conservative terrain choices along with selective avoidance of high-consequence avalanche terrain will be imperative to manage your risk until the snowpack gains strength.
Terrain and Travel
- 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 from the alpine down into the upper treeline and the consequences for triggering it are severe. This layer has been responsible for many very large avalanches in the region over the past two weeks. Shallower storm slab releases may step down to this layer and create a very large, very destructive avalanche.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
30-100 cm of snow from the recent storm formed slabs over a weak layer of surface hoar in sheltered areas from 1800-2200 metres. This layer continues to produce concerning snowpack test results and may fail under the weight of a person or machine. Storm slab avalanches may also step down to an even deeper buried weak layer, forming destructive avalanches that could travel far.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 26th, 2019 5:00PM