Avalanche Forecast

Issued: Dec 2nd, 2021 4:00PM

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

Avalanche Canada bchristie, Avalanche Canada

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Wind slabs can still be triggered by riders. Also be aware that rapidly forming wind and storm slabs can naturally avalanche.

Monitor wind and new snowfall as you travel through terrain, and make more conservative choices if you find signs of instability.  

Summary

Confidence

Moderate - We are confident about the likelihood of avalanche activity, what is less certain are their possible size.

Weather Forecast

Thursday Night: Overcast with potential breaks in cloud. 0-5cm new snow. Strong southwest wind. Alpine temperature around -13 C.

Friday: Mostly overcast. 5-15 cm new snow. Strong southwest wind. Alpine temperature around -12 C.

Saturday: Partly Cloudy. Possible trace of new snow. Moderate northwest wind. Alpine temperature around -14 C.

Sunday: Mostly Cloudy. 0-5 cm of new snow possible in the afternoon. Moderate southwest wind. Alpine temperature around -12 C.

Avalanche Summary

On Wednesday morning, a few small natural avalanches were observed and explosive and machine control work produced size 1-2 storm slab avalanches.

Near Stewart, there is evidence that a widespread avalanche cycle occurred during the past storm, up to size 3 in wind loaded terrain at treeline and in the alpine. 

On Tuesday morning, several size 2 storm slabs were reported to have run naturally during the storm.

Snowpack Summary

Up to 30 cm of snow in the last 36 hours continues to be redistributed and built into slabs by moderate to strong winds. The most recent snow is less dense than the last week, but it can still form reactive slabs.

The new snow overlies a variable surface produced by the previous, warmer, wetter, windier storms. Snow had been stripped from ridgetops and exposed terrain and loaded into lee terrain features and cross-loaded slopes by strong to extreme wind at upper elevations. At elevations below treeline where the snow hasn't been washed away altogether, expect to find a crust under the new snow.

A crust that formed as high as 1600 m during a previous warm November storm is now 60-100 cm deep. Wind slabs have shown good propagation where they sit directly over this slick sliding surface.

In the Northern part of the region (Bear Pass) two weak layers of surface hoar from early to mid November have been reported in sheltered areas at treeline.

Treeline snowpack depths are estimated to be around 2-3 m, and a prominent crust can be found near the base of the snowpack.

Terrain and Travel

  • Be alert to conditions that change with elevation and wind exposure.
  • Avoid lee and cross-loaded slopes at and above treeline.
  • A crust on the surface will help bind the snow together, but may make for tough travel conditions.
  • Keep in mind the crust offers an excellent bed surface for avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs

A potential push of fresh snow moves us back into watching for storm slabs at all elevations, but don't forget that in the last week, strong to extreme winds formed thick wind slabs in lee terrain features and cross-loaded slopes at upper elevations.

 

An avalanche in the new storm snow may trigger a deeper windslab underneath.

Slabs may be especially reactive where they sit on top of a slick crust. 

Cornices have reportedly formed along ridgelines. Cornice failures can trigger avalanches on the slope below.

 

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Valid until: Dec 3rd, 2021 4:00PM