Avalanche Forecast

Issued: Nov 28th, 2022 4:00PM

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

Avalanche Canada jpercival, Avalanche Canada

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Conservative terrain travel is recommended until the snowpack has time to heal. All the recent storm snow overlies a layer of concern that has been producing natural avalanches.

Summary

Confidence

Moderate

Avalanche Summary

Many new natural and human-triggered avalanches have been reported in the alpine and at the treeline, between 1700 and 2200 m. The common theme is that they are failing on the November 21st / surface hoar facet crust interface.

Additionally, the terrain where these avalanches occurred was steep and focused on north through to east-facing terrain. The size of these avalanches has been from size 1 (small) to size 3 (very large).

One avalanche, in particular, was remotely triggered by a skier and began as a size one and picked up enough mass to strip the snowpack to the ground resulting in a size 2.5 ( large) avalanche. Temperatures are forecast to remain cool and I would surmise that this slab avalanche problem will continue to persist.

Snowpack Summary

A series of storms over the past week has delivered 30 to 50 cm of new snow. This snow fell during a period of cooling and is light and easily transported by the wind.

A layer that was buried November 21st can be found down between 50 to 80 cm and is primarily a mix of surface hoar and faceted crystals. This layer is the primary concern of persistence and has been the key component of the recent natural avalanche cycle.

The average snowpack depth below the treeline is 40 to 70 cm and above that elevation is 100 to 150 cm, with wind-loaded areas presenting as 200 cm.

Weather Summary

Monday Night

Partly cloudy with very isolated flurries, accumulation 1 cm, 10 to 20 km northeast wind, treeline temperature -15 to -20 C.

Tuesday

Mostly clear skies with light precipitation near the day's end, 10 km/h buildings to 40 km/hr southwest wind, treeline temperature -20 to -25 C.

Wednesday

Increasing cloud with isolated afternoon flurries, accumulation 1 to 3 cm, 10 km/h southeast wind, treeline temperature -17 to -20 C.

Thursday

Cloudy with snowfall, accumulation 10 cm, 20 to 40 km/h southeast wind, treeline temperature -15 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Choose conservative terrain and watch for clues of instability.
  • Make observations and assess conditions continually as you travel.
  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.

Problems

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Very Likely

Expected Size

1.5 - 3

Around 40 to 80 cm of snow from the past week is forming a slab that may not bond well to the underlying snowpack. The interface of concern formed during mid-November and is composed of faceted grains, surface hoar, and a hard crust. To date the layer has been most problematic above 1700 m.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Nov 29th, 2022 4:00PM

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