Avalanche Forecast

Issued: Dec 15th, 2021 4:00PM

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

Avalanche Canada astclair, Avalanche Canada

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Watch for changing conditions in wind-exposed areas. If winds pick up, fresh reactive wind slabs are likely to form. Avoid slopes where a slab is stiffening above a persistent weak layer. 

Summary

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Wednesday night: Scattered clouds, no new snow expected, light to moderate southwest winds trending westerly at higher elevations, alpine temperatures near -13 C.

Thursday: Partly cloudy, a trace of snow possible, light to moderate southwest winds trending westerly with strong gusts at higher elevations, alpine high temperatures near -8 C.

Friday: Mostly clear, up to 5 cm of snow expected overnight, light west winds increasing to moderate at higher elevations, alpine high temperatures near -11 C.

Saturday: Partly cloudy, up to 5 cm of new snow, southwest winds increasing to moderate with strong to extreme westerly winds in the alpine, alpine high temperatures near -5 C.  

Avalanche Summary

It may be possible to trigger slab avalanches in wind-drifted areas at upper elevations or where a slab overlies weak snow on a crust. 

Over the last two day, operators have reported several large (size 2) explosive-triggered avalanche releasing on the early December crust layer. 

Observations from last weekend indicated that the snowpack was quite touchy. Avalanche control with explosives and ski cuts produced several size 2 avalanches, and one size 3. Most failed on top of the rain crust from the late November/early December rain events.

Snowpack Summary

Up to 20 cm of snow has accumulated since Monday with very little wind. This fresh snow likely remains unconsolidated, except where the wind is drifting it into denser slabs at upper elevations. 

Below this layer, more consolidated snow from the previous weekend storm sits over a substantial crust that formed in early December. This crust is likely 20 cm thick (or more) and is present across aspects below 2400m. A thin layer of weak facets (sugary snow) can found above this crust that has demonstrated reactivity in snowpack tests and avalanche activity. 

Snowpack depths vary due to strong to extreme southwest winds from early December that stripped snow off of exposed areas and deposited it onto lee slopes. Below 2300m, several early season crusts are breaking down and forming a cohesive lower snowpack. Snowpack depths range from 60-110 cm at treeline elevations and taper quickly below 1900m.

Terrain and Travel

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Make observations and assess conditions continually as you travel.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Uncertainty is best managed through conservative terrain choices at this time.

Problems

Wind Slabs

An icon showing Wind Slabs

It may be possible to trigger avalanches in the recent snow where it is getting drifted by wind at upper elevations. 

Aspects: North, North East, East, South East, South, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

A layer of weak facets (sugary snow) can be found down 40-70 cm over a crust that formed in early December. This layer has recently produced large avalanches from explosive triggers and warrants conservative terrain selection.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Valid until: Dec 16th, 2021 4:00PM