Avalanche Forecast

Issued: Feb 5th, 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 ahanna, Avalanche Canada

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Watch for reactive wind slabs in lee terrain features at upper elevations. Uncertainty around buried weak layers is best managed through conservative terrain selection.

Summary

Confidence

High -

Weather Forecast

Friday night: Mainly cloudy, moderate to strong northwest ridgetop wind, alpine temperature -7, freezing level 500 m.

Saturday: Mainly cloudy, moderate to strong westerly wind, alpine high -7, freezing level 900 m.

Sunday: Mix of sun and cloud, light westerly wind, alpine high temperature -10, freezing level valley bottom.

Monday: Mix of sun and cloud, light northwest wind, alpine high temperature -12, freezing level valley bottom.

Avalanche Summary

Skier triggered wind slabs up to size 1.5 were reported on Thursday. Explosive control work conducted over the last few days have produced size 2 cornice and storm slab avalanches.

Earlier in the week, many of the numerous size 1-2 natural, human and explosives triggered avalanches were reported to have failed on the recently buried persistent weak layer.

Snowpack Summary

Westerly winds are likely redistributing surface snow into wind slabs in leeward terrain features at upper elevations. 50-100 cm of recent snow sits on a persistent weak layer that consists of facets at upper elevations, surface hoar in sheltered areas, a melt-freeze crust below 1900 m, and a sun crust on south-facing slopes. There could be more than 100 cm on this layer in wind loaded areas.

A crust from early December may be found around 200+ cm deep in the snowpack. In shallow rocky areas, it may still be possible to trigger this layer. In deeper snowpack areas, it appears to be unreactive.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be aware of highly variable recent wind loading patterns.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

Problems

Wind Slabs

An icon showing Wind Slabs

Wind slabs may remain reactive to human triggers. Be aware of the potential for wind loading on a variety of aspects including atypical terrain features on southerly aspects due to recent northerly wind.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

50-100 cm of snow sits on a widespread weak layer that consists of facets, surface hoar, or a crust depending on location. Avalanches may propagate widely on this layer.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Valid until: Feb 6th, 2021 4:00PM