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Avalanche Forecast

Archived

Dec 28th, 2020–Dec 29th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Rockies.

It's a classic rockies snowpack out there: be careful of shallow rocky snowpacks where its possible to trigger deeper weak layers and watch out for fresh wind slabs that are forming in windy alpine zones and exposed ridge crests near tree line.  

Confidence

Moderate - Confidence is due to a stable weather pattern; little change is expected for several days. Uncertainty is due to the limited number of field observations.

Weather Forecast

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

Monday night: Clear with cloudy periods. Alpine low temperatures near -10C and freezing levels valley bottom. Ridgetop wind moderate gusting strong from the northwest. A mild alpine temperature inversion may bring valley clouds and warmer clear temperatures above.

Tuesday: A mix of sun and clouds. Alpine high temperatures near -8C and freezing levels dropping to valley bottom. Ridgetop light gusting moderate from the northwest. We may see wind enhancement along the divide leading to strong northwest winds.

Wednesday: A mix of sun and clouds. Alpine high temperatures near -8C and freezing levels dropping to valley bottom. Ridgetop wind moderate gusting strong from the southwest/west.

Thusday: A mix of sun and clouds. Alpine high temperatures near -8C and freezing levels dropping to valley bottom. Ridgetop wind moderate gusting strong from the southwest/west.

Avalanche Summary

Recent avalanche activity includes an explosive triggered large wind slab avalanche from the 27th and loose dry sloughing to size 1 from steep terrain.  

A large avalanche cycle occurred last week following recent snow and strong winds that included wide spread large avalanches and a few very large avalanches. These avalanches were predominately wind slabs, but a few step downed to deeper weak layers.  

Sluffing of loose dry snow is building mass to size 1 from steep wind sheltered terrain.

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 re-distributed by moderate to strong winds in exposed treeline and above. Moderate to strong winds in the alpine have been reported across and to the east of the divide, and will continue to transport snow and build wind slabs in lee features. Cornice development may be found along ridgecrests and deep windslabs on lee slopes

 A crust from early December is down 50-100cm. This persistent weak layer, with facetted crystals and surface hoar crystals above and/or below is showing signs of slowly gaining strength. However, smaller avalanches or a cornice failure may step-down to this weak layer. 

The base of the snowpack consists of a hard melt-freeze crust / facets from early-November which remains on our radar. This layer produced very large and destructive avalanches in shallower snowpacks within one of our nearest neighbours during the last avalanche cycle, highlighting the need to remain cautious of it in shallow, rocky alpine snowpacks. 

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid areas where the snow feels stiff and/or slabby.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • 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.