Avalanche Forecast

Issued: Dec 20th, 2019 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada mconlan, Avalanche Canada

A substantial amount of recent snow has accumulated, which is loading a buried weak layer. Conservative decision-making is essential to safely manage the avalanche problems.

Summary

Confidence

High -

Weather Forecast

FRIDAY NIGHT: Cloudy with light snowfall, accumulation 2 to 5 cm, moderate southwest wind, alpine temperature -6 C, freezing level 1000 m.

SATURDAY: Mostly cloudy with isolated flurries, accumulation 2 to 5 cm, light to moderate southwest wind, alpine temperature -7 C, freezing level 1000 m.

SUNDAY: Cloudy with snowfall and afternoon clearing, accumulation 10 to 20 cm, moderate to strong southwest wind, alpine temperature -7 C, freezing level 1000 m.

MONDAY: Mix of sun and cloud, light west wind, alpine temperature -8 C, freezing level below valley bottom.

Avalanche Summary

Many large slab avalanches were triggered naturally and by explosives on Friday. 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 scrubbed to the ground.

Human-triggered avalanches are expected to be likely to occur on Saturday, with the potential to fail in both the recent storm snow as well as the mid-November weak layer. Conservative decision-making is essential given this weak snowpack.

Snowpack Summary

Around 50 to 80 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 around 50 to 100 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. Read this informative Mountain Conditions Report for more information on this persistent avalanche problem.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Make conservative terrain choices and avoid overhead hazard.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.

Problems

Storm Slabs

An icon showing Storm Slabs

Around 50 to 80 cm of recent snow fell with strong to extreme southwest wind. Expect to find touchy storm and wind slabs until this snow bonds to the snowpack. Human-triggered avalanches are likely to occur on Saturday. 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

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing 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. The likelihood of triggering this layer may slowly decrease in the coming days, but the consequence of triggering it would be severe. This snowpack setup is atypical for the region, which will require diligent terrain travel and conservative decision-making until the weak layer strengthens.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1.5 - 3

Valid until: Dec 21st, 2019 5:00PM