Avalanche Forecast

Issued: Jan 8th, 2020 4:30PM

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

Avalanche Canada astclair, Avalanche Canada

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Although snowfall has tapered, avalanche conditions remain complicated and dangerous. Stick with conservative terrain choices and give the snowpack time to adjust.

Summary

Confidence

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

Weather Forecast

Wednesday night: Decreasing cloud, moderate west wind, alpine temperature -16 C.

Thursday: Increasing cloud, isolated flurries with trace accumulations, light west wind, alpine high temperature -11 C.

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

Saturday: Cloudy, 5-10 cm of snow, light south wind, alpine high temperature -9 C. 

Avalanche Summary

A widespread avalanche cycle occurred overnight and into Wednesday. Numerous large (size 2-2.5) and very large (size 3-3.5) avalanches released from natural, human, and explosive triggers in the storm snow. The majority of the human-triggered avalanche activity occurred where the wind played a role in stiffening slabs, particularly below ridge crests.

Prior to the storm, there were many reports of large (size 2-3) avalanches from both natural and human triggers on a variety of aspects and elevations. These avalanches were breaking 50-100 cm deep on surface hoar layers from mid to late December. Several of them were remote-triggered. The most recent example, reported Monday, released naturally with loading from new snow and wind. These avalanches give clear evidence that the continual loading on this fundamentally weak snowpack structure remains a concern.

Within the past week, three notable deep 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. 

Snowpack Summary

The most recent storm delivered 30-70 cm of new snow across the region with moderate to strong southwest winds. Expect storm slabs to be especially touchy in lee terrain features where southwest winds have been drifting new snow into stiffer, more reactive slabs. Periods of sun possible on Wednesday have the potential to promote instability in the storm snow on sun-affected slopes.  

Two layers of surface hoar from mid and late December are now buried 60-140 cm deep. These layers continue to produce large avalanches across aspects and elevations. Small avalanches in the new snow have the potential to step-down to these persistent weak layers.

A facet/crust layer from late November lingers near the bottom of the snowpack. This layer has shown reactivity in isolated areas in the southern part of the region.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • 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

The most recent storm delivered 30-70 cm of snow across the region forming reactive storm slabs. With moderate to strong southwest winds, storm slabs will be more pronounced in lee terrain features at higher elevations. Periods of sun possible on Wednesday have the potential to promote instability in the storm snow on sun-affected slopes.  

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

Two layers of surface hoar from late December are now buried 60-140 cm deep. Recent significant loading from new snow has the potential to bring these weak layers to their tipping point and to create conditions for step-down avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Jan 9th, 2020 5:00PM