Avalanche Forecast

Issued: Jan 6th, 2020 4:30PM

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 astclair, Avalanche Canada

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A juicy storm impacts the region Tuesday creating very dangerous avalanche conditions. Travel in the backcountry will require a cautious mindset and conservative terrain choices.

Summary

Confidence

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

Weather Forecast

Monday night: Cloudy, 10-20 cm of snow, light southwest wind, alpine temperature -6 C.

Tuesday: Cloudy, 20-30 cm of snow, moderate southwest wind, temperatures warming throughout the day with a high of -2 C in the late afternoon, freezing level rising to 1000 m.

Wednesday: Cloudy, 20-30 cm of snow overnight, moderate southwest wind, alpine high temperature -3 C, freezing level dropping to valley bottom.

Thursday: Partly cloudy, light northwest wind, alpine high temperature -9 C. 

Avalanche Summary

New snow and wind are expected to induce a natural avalanche cycle. More reactive storm slab avalanches have the potential to step down to multiple buried weak layers producing large and destructive avalanches. 

Over the weekend, there were reports of large (size 2-3) avalanches breaking on a layer of surface hoar from late or mid-December on a variety of aspects and elevations from natural, human, and explosive triggers. A few of these avalanches were triggered remotely (i.e. from a distance). Three notable persistent slab avalanches released naturally on east and northeast facing slopes above 2200 m in the southern part of the region on a crust/facet layer from late November buried 150 cm deep. These avalanches give clear evidence that the continual loading on this fundamentally weak snowpack structure remains a serious concern.

Snowpack Summary

The incoming storm is forecast to bring 30-40 cm of snow to the region throughout the day on Tuesday with moderate southwest wind, forming a new storm slab problem that will need to be managed. Expect areas where the snow is being drifted by wind to more rapidly develop this storm slab problem.

There are multiple weak layers buried in the snowpack. A weak layer of feathery surface hoar is buried around 60 to 100 cm deep. Around 110 to 150 cm deep, another surface hoar layer may be found, and a facet/crust layer from late November lingers near the bottom of the snowpack. This fundamentally unstable snowpack structure remains a concern, as it is capable of producing large and destructive avalanches. It is possible that storm slab avalanches could step down to these deeper layers or that the layers could be triggered in areas where the snowpack is relatively thin.

Terrain and Travel

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs

Storm snow is expected to accumulate throughout the day, and favored areas in the region may see 30-40 cm. Moderate southwest winds are expected to increase slab reactivity in drifted areas.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

Several persistent weak layers are buried in the snowpack. Although these layers become harder to trigger as they get deeper, the destructive potential of a triggered avalanche increases. These layers could be triggered by humans where the snowpack is relatively thin or a storm slab avalanche could step down to them. 

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Jan 7th, 2020 5:00PM