Avalanche Forecast

Issued: Dec 28th, 2020 5:00PM

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

Avalanche Canada cmortenson, Avalanche Canada

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Continue to make conservative terrain choices: buried weak layers exist in the snowpack. Be cautious with steep and / or convex terrain and look for signs of instability: recent avalanches, hollow drum-like sounds from wind slabs, shooting cracks or wumping.  

Summary

Confidence

Moderate - Confidence is due to a stable weather pattern; little change is expected for several days.

Weather Forecast

High pressure influences the region for the forecast period with cool temperatures, isolated flurries, light winds gusting moderate/strong from the northwest and a mix of sun and clouds.  

Monday night: Cloudy with clear periods and isolated flurries. Alpine low temperatures near -11C and freezing levels valley bottom. Ridgetop wind light gusting moderate from the west.

Tuesday: Mix of sun and cloud. Alpine high temperatures near -11 and freezing levels valley bottom. Ridgetop wind light gusting moderate from the northwest.

Wednesday: Mix of sun and cloud with isolated flurries. Alpine high temperatures near -7 and freezing levels valley bottom. Ridgetop wind moderate gusting strong from the west.

Thursday: Mostly cloudy with isolated flurries and sun breaks. Alpine high temperatures near -8C and freezing levels valley bottom. Ridgetop wind light gusting moderate from the west/northwest.

Avalanche Summary

Wind slab avalanches continue to be triggered though they appear to be more stubborn and isolated. Sluffing of loose dry snow is building mass to size 1 from steep wind sheltered terrain. 

Last week there was a significant avalanche cycle from heavy snow and strong winds. This cycle produced a few very large avalanches, including some that stepped down to deeper crusts and one that stepped down to the November crust in a nearby neighbour.  

Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter!

Snowpack Summary

30-60 cm snow that fell last week has been blown by moderate to strong winds created snow re-distribution onto lee slopes. Cornice development may be found along ridgecrests and deep windslabs on lee slopes. 

Recent snow fell on a variety of old surfaces including a buried melt-freeze crust reported below 1700m and surface hoar reported around treeline. 10-20cm low density snow cover this recent crust below 1800m. 

Buried 60-95cm one can find a variety of weak layers from early December. This persistent weak layer, with facetted crystals and surface hoar crystals above is starting to gain strength. This MIN from the 27th near Mongolia Bowl reports finding this crust at 60cm with no notable results in their test pits while this MIN form the 26th saw varying results - including a deep hard result on basal layers.

Deeper in the snowpack are two hard melt-freeze crusts with facets from early November. This potential avalanche problem remains on our radar. This layer produced very large and destructive avalanches in shallower snowpacks within one of our nearest neighbours during the recent large cycle.  

Terrain and Travel

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Watch for areas of hard wind slab on alpine features.
  • Approach lee and cross-loaded slopes with caution.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

Problems

Wind Slabs

An icon showing Wind Slabs

Be on the lookout for wind-loading in lee slopes from a variety of westerly wind directions. Older buried windslabs and cross-loaded features should also be suspect. Large cornice have formed: these are a hazard underfoot as well as being an overhead hazard that is capable of triggering large avalanches should they fail.

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

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

Depending on elevation and aspect, 60-150 cm of snow currently sits above buried weak layers from early December. Sugary, facets and surface hoar around the crust mean persistent slabs remain reactive, especially with large triggers or in a shallow snowpack. This layer appears to be more concerning above 1700m and on northerly aspects. This layer proceed avalanches last week. It remains possible to tigger this layer in thin to fat zones, with a step-down avalanche, with a cornice collapse or on slopes that have received significant wind transport. 

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Dec 29th, 2020 5:00PM

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