Avalanche Forecast

Issued: Nov 23rd, 2019 5:00PM

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

Avalanche Canada astclair, Avalanche Canada

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30+ cm of new snow is expected in the northern parts of the region, which will likely result in two things:

1. A touchy storm slab problem

2. Potentially wake up the persistent slab problem

Choose simple terrain on Sunday as the snowpack adjusts to the load of new snow.

Summary

Confidence

Low - Uncertainty is due to the complexity of the snowpack’s structure. Uncertainty is due to how the snowpack will react to the forecast weather. Uncertainty is due to the limited number of field observations.

Weather Forecast

Saturday night: Another 10-20 cm of snow above 1400 m with moderate to strong southwest winds. 

Sunday: Broken cloud cover, moderate winds shifting to the west/northwest, freezing level around 1000 m and dropping, continued flurries with 5-10 cm of additional accumulation possible.

Monday: Clearing skies, freezing level near valley bottom, light northwest winds, no significant precipitation expected.

Tuesday: Clear, calm, cold, dry.

Avalanche Summary

Very little avalanche activity has been reported over the last week but anticipate another avalanche cycle this weekend. As storm snow accumulates, human-triggered avalanche activity is likely. 

If you see anything while out in the field, please consider sharing that information with us and the backcountry community via the Mountain Information Network (MIN)

Snowpack Summary

Winter ramps up this weekend as the latest storm brings fresh snow, heightened avalanche hazard, and a good test for our snowpack. 

Snow totals of around 30 cm should accumulate by Sunday morning, with winds primed for snow transport. The northern parts of the region should see the highest snowfall amounts. The new snow is unlikely to bond well with the previously wind-affected surfaces in the alpine and with the crust and surface hoar that developed near and below tree line. This rapid load may also trigger deeper weak layers formed in mid-November and late October that are now down 40-80 cm. 

This storm brings winter lower into the valleys, as snowline could drop to 1000 m. Current total snowpack depths range from about 60 cm below treeline to as high as 170 cm in the alpine. 

Problems

Storm Slabs

An icon showing Storm Slabs

Storm totals could exceed 30 cm with a fair amount of wind by Sunday morning. This new layer is unlikely to bond well to the underlying old snow surface and could be easy to trigger. If enough snow accumulates, this problem could be suspect below tree line, especially in the higher reaches of the elevation band where the interface consists of surface hoar on a crust.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

The rapid load of new snow will be a good test for a buried crust found 40 to 80 cm below the surface of the snowpack. This weekend's storm could potentially wake up this persistent weak layer, and avalanches failing on this interface could be surprisingly large. Given the uncertainty with its likelihood and the severity of its consequences, this persistent slab problem warrants conservative terrain choices.  

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Nov 24th, 2019 5:00PM