Avalanche Forecast

Issued: Dec 22nd, 2021 4:00PM

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

Avalanche Canada dboucher, Avalanche Canada

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Recent major storm has develop significant storm slabs that remain reactive with the potential to step-down and trigger deeper buried weak layer. Avoid avalanche terrain and wait for conditions to improve.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Snow continues as moisture will persist in the extreme south of the province, favouring additional snowfall for the South Coast mountains.

Wednesday night: Snow, 10 to 20 cm, strong to extreme southwesterly winds, low treeline temperatures near -5 C with freezing level around 800 m.

Thursday: Flurries, 5-10 cm, strong westerly winds, high treeline temperatures near -10 C with freezing level going back to valley bottom.

Friday: Flurries, 5 cm, moderate northeasterly winds, high treeline temperatures near -13 C with freezing level at valley bottom.

Saturday: Flurries, 5 cm, light to moderate northeasterly winds, high treeline temperatures near -15 C with freezing level at valley bottom.

Avalanche Summary

Although avalanche activity has momentarily tappered off on Monday and Tuesday, we are expecting natural avalanche activity to continue on Thursday with additional storm snow and strong southwesterly. Storm slabs avalanches have the potential to step-down to recently reactive buried weak layers, with the potential to produce very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below.

Snowpack Summary

The ongoing storm has the potential to add 40 to 65 cm to the 30 to 50 cm layer of settling snow from last weekend's storm. All this new snow sits on a variety of snow surfaces, hard wind-scoured surfaces, preserved powder, and possible surface hoar in sheltered areas. Strong southerly winds will continue to redistribute the storm snow into dense wind slabs on leeward terrain features.

A culprit weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 70-150 cm). This layer seems particularly reactive at lower alpine and treeline elevations, between 1500-2100 m. Large size 2 and 3 avalanches on this persistent slab problem have been reported over the past few days in the neighbouring Sea-to-Sky region. This problem is particularly hard to predict and tricky to manage. Given the rapid load from the ongoing storm and wind, this persistent slab problem requires to scale back and wait for conditions to improve. Get more details and photos in our forecaster blog. 

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Give the new snow time to settle and stabilize before pushing into bigger terrain.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.

Problems

Storm Slabs

An icon showing Storm Slabs

Storm snow and strong southwesterly winds have developed large storm slabs we expect to continue to be reactive troughout the day.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1.5 - 3

Persistent Slabs

An icon showing Persistent Slabs

A layer of weak facets (sugary snow) can be found down 70-150 cm near a crust that formed in early December. Storm slabs in motion may step down to this layer and trigger large destructive avalanches. Also, it is more likely to human trigger this persistent slab in thick to thin areas at tree line elevations.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Valid until: Dec 23rd, 2021 4:00PM

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