Avalanche Forecast

Issued: Jan 7th, 2020 4:30PM

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

Avalanche Canada astclair, Avalanche Canada

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Rapid loading from snow and wind on a reactive buried weak layer is creating very dangerous avalanche conditions. If triggered, avalanches could break deeper, propagate wider, and travel farther than anticipated. Travel in avalanche terrain is not recommended.

Summary

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Tuesday night: Cloudy, 15-25 cm of snow, moderate to strong southwest wind, alpine temperature -7 C.

Wednesday: Cloudy, isolated flurries with trace accumulations, moderate west wind, alpine high temperature -10 C.

Thursday: Mix of sun and cloud, isolated flurries with trace accumulations, light west wind, alpine high temperature -12 C. 

Friday: Cloudy, 5-15 cm of snow, strong south wind, alpine high temperature -10 C.

Avalanche Summary

There have been many reports of large (size 2-2.5) avalanches from both natural and human triggers on a variety of aspects and elevations releasing on a surface hoar layer formed in late December. These avalanches have been breaking 80-120 cm deep. Several of them have been remote-triggered, like the one in this MIN from Wednesday.

Be sure to check out this MIN, this MIN, and this MIN for helpful illustrations of slopes that are likely to harbor this problem. A sincere thanks to the community for submitting these reports!

As the new snow settles, storm slab avalanches are likely to be triggered and have the potential to step down to these deeper layers, forming very large and destructive avalanches.

Snowpack Summary

20 to 35 cm of snow is forecast to accumulate by Wednesday afternoon with moderate to strong southwest wind. Expect storm slabs to be especially touchy in lee terrain features.

A very concerning layer of surface hoar from late December is now buried 80-120 cm deep. This layer formed in late December and continues to produce large avalanches across aspects and elevations. Recent snowpack tests have confirmed this weak layer's propagation potential (check out this MIN from Saturday).

Terrain and Travel

  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Choose simple, low-angle, well supported terrain without convexities.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs

20-35 cm of total storm snow is forecast to accumulate forming new, reactive storm slabs. There is potential for storm slabs to step down to deeper weak layers, forming large and destructive avalanches. Storm slabs will be more pronounced in lee terrain features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

A very concerning layer of surface hoar from late December is now buried 80-120 cm deep. This layer has produced many large avalanches across aspects and elevations with incremental loading from new snow and wind. A few of these avalanches were human-triggered remotely from adjacent slopes. This problem warrants a wide margin with very conservative travel decisions.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 3

Valid until: Jan 8th, 2020 5:00PM