Boletín de aludes

South Rockies

Dec 29 – 30, 2020Avalanche Canada
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Archivado · caducó 6 years ago

Peligro de aludes

Thu
Fri
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Lo esencial

It's a classic Rockies snowpack out there. Be careful of shallow rocky slopes where it's possible to trigger deeper weak layers. Watch out for fresh wind slabs that are forming in windy alpine zones and lee of exposed ridge crests near treeline.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Be on the lookout for fresh wind slabs forming on lee east/southeast slopes in areas with moderate to strong winds. Winds have been variable, so assess leeward slopes carefully for wind loading. Observe wind effect like scouring, sastrugi, cross-loading and lee deposition for clues to how recent winds have reworked the terrain. Large cornices have formed: these are a hazard underfoot as well as being an overhead hazard that is capable of triggering large avalanches should they fail

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely - Possible
    Tamaño
    1.5–3

    50-100 cm of snow currently sits above a weak layer from early December. Combinations of a crust, sugary facets , and/or surface hoar mean persistent slabs can produce large destructive avalanches. It remains possible to tigger this layer in thin to fat zones, with a cornice collapse, with a step-down avalanche or on slopes that have received significant wind transport.  

    In very shallow snowpacks, basal facets and a crust / facet layer from early November remain on our radar. Large and very large avalanches were reported on this layer last week from one of our nearest neighbours.  

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.

Confidence

Moderate - Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region. 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, 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. 

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