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Avalanche Forecast

Archived

Dec 29th, 2020–Dec 30th, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Enjoy the best and safest riding in wind sheltered locations. Remain cautious with shallow/rocky snowpacks were it is possible to trigger buried weak layers and a large avalanche.

Confidence

High - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Tuesday night: Mainly clear, alpine low temperatures -11C, freezing levels valley bottom & ridgetop winds moderate west.  

Wednesday: A mix of sun and clouds, alpine high temperatures -6C, freezing levels valley bottom & ridgetop winds moderate to strong west/southwest.

Thursday: A mix of sun and clouds, alpine high temperatures -6C, freezing levels valley bottom & ridgetop winds moderate to strong from the southwest/west.

Friday: A mix of sun and clouds with isolated flurries, trace - 5cm new snow, alpine high temperatures -3C, freezing levels1500m & ridgetop winds moderate to strong southwest/west.

Avalanche Summary

Limited recent avalanches have been reported in recent days. On the 27th there was an explosive triggered large wind slab avalanche and loose dry sloughing to size 1 from steep terrain.  

There was a large avalanche cycle last week following heavy snow falls and strong winds that included widespread large avalanches and a few very large avalanches. These avalanches were predominately wind slabs, but a few stepped down to deeper weak layers. One notable very large avalanche in a neighbouring forecast region stepped down the crust and facets at the bottom of the snow pack, highlighting the need to make conservative terrain decisions in shallow, rocky alpine snowpacks. 

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

Snowpack Summary

Recent winds have re-worked snowpacks in exposed ridgecrests and alpine areas leading to scouring, cross-loading and widespread wind slabs in lee features. Wind direction has been variable, but largely from the southwest loading north and east aspects.

 A crust from early December is down 40-90 cm. This persistent weak layer, with facetted crystals and surface hoar crystals above and/or below is showing signs of slowly gaining strength, as reported in this MIN from Mear Lake.

The base of the snowpack consists of a hard melt-freeze crust / sugary facets from early-November which remains on our radar. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid areas where the snow feels stiff and/or slabby.
  • Approach lee and cross-loaded slopes with caution.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.