Avalanche Forecast

Issued: Nov 29th, 2020 4:00PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Deep Persistent Slabs.

Avalanche Canada JSmith, Avalanche Canada

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Lingering wind slabs may remain surprisingly reactive to human triggers in areas where they are sitting on a layer of small surface hoar. Additional snow and shifting northwest winds on Monday may create fresh wind slabs.

Summary

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

SUNDAY NIGHT: Mostly cloudy / Moderate, southwest wind / alpine low temperature -12 / Freezing level valley bottom.

MONDAY: Snow, 5-15 cm / Light to moderate, northwest wind / alpine high temperature -6 / Freezing level 800 m.

TUESDAY: Sunny / Light, northwest wind / alpine high temperature -7 / Freezing level valley bottom.

WEDNESDAY: Sunny / Light, south wind / alpine high temperature +2 / Strong inversion with an above freezing layer of air above 2000 m.

Avalanche Summary

There have been very few reports of avalanches in the region, however, observations are very limited at this time. 

Several recent MIN reports from neighboring Glacier National Park have reported human triggered avalanches on small surface hoar below the recent storm snow.

If you get out into the mountains, please consider sharing your observations on the Mountain Information Network!

Snowpack Summary

 Recent strong southwest winds have created wind slabs on lee features at treeline and above. These wind slabs may be surprisingly reactive in areas where they are sitting on a layer of small surface hoar. There are a couple of crusts in the mid snowpack, from mid and early November. The most prominent of these is from early November, and it has been reported that there are weak, sugary facets above and below this crust. It is down approximately 70-100 cm, and is most likely to be reactive to human triggers on south facing slopes and in shallow, rocky, snowpack areas in the alpine.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid lee and cross-loaded terrain.

Problems

Wind Slabs

An icon showing Wind Slabs

  

Recent strong southwest winds have created wind slabs on lee features at treeline and above. These wind slabs may be surprisingly reactive in areas where they are sitting on a layer of small surface hoar.   

Additional snow and shifting northwest winds on Monday may create fresh wind slabs.  

Aspects: North, North East, East, South East, South, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

A crust from early November exists down about 70-100 cm. This layer has weak, sugary facets above and below it. This layer is most likely to be reactive to human triggers on south facing slopes and in shallow, rocky, snowpack areas in the alpine.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Nov 30th, 2020 4:00PM

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