Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Dangerous avalanche conditions continue throughout our forecast region.  Additional new wet snow and rain have added more weight to our existing weak snowpack.  Gale force winds will also continue to form large slabs of wind drifted snow.  Large and destructive avalanches have occurred over the last 3 days and are expected again today.  Conservative terrain choices and decision making are critical.  

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    We continue to be in the midst of a persistent slab avalanche cycle.  A weak snowpack structure with sugary faceted snow now exists 1 to 3+ feet deep under the recent storm snow since Thursday of last week.  The more recent wet heavy snow and rain have added considerable weight to this weak layer. The persistent weak layer exists on NW-N-NE-E aspects, but could also be found in isolated areas on other aspects.  Large natural and human triggered avalanches have been reported over the past 3 days and are expected to occur today.  These avalanches can propagate wider than expected, wrap around terrain features, and travel farther downhill than usual.  These avalanches could be remotely triggered from below or other areas where connected terrain exists.  In areas where rain has fallen on the snow, these avalanches could also have some wet snow characteristics.   

    Recent avalanche activity, shooting cracks, whumpfing, and collapsing represent clear signs of instability.  Increase safety margins by steering clear of any terrain steeper than 30° or terrain connected to/below steep slopes.  Avoid areas below steep slopes as these avalanches could run long distances .

    (12/2/2022)

    Remotely triggered avalanche on the N side of Castle Peak

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    Additional snow and gale force winds will continue to build out wind slabs on NW-N-NE-E-SE aspects in near and above treeline areas.  These wind slabs will form on top of wind slabs that formed yesterday that have not fully bonded to the snowpack below them.  Large wind slab avalanches will remain likely today.  These avalanches could run longer than usual and trigger persistent slab avalanches as they move downhill.

    Use clues like blowing snow, cornices above a slope, drifted snow, or other wind-created surface textures to help evaluate which slopes hold wind slabs. Choose travel routes that avoid these wind-loaded areas. Cautious route-finding focusing on lower-angle terrain not connected to steeper terrain can help avoid both avalanche problems today. 

Avalanche Discussion

  • People remotely triggered several large avalanches that failed on the buried facet layer on Friday. These occurred on Castle Peak, in the Deep Creek drainage, on Jakes Peak, and on Carpenter Peak.  Fortunately, no one was caught in these avalanches. 
  • Backcountry users reported whumpfing, snowpack collapsing, and shooting cracks over the last 3 days all across the forecast area on a variety of aspects and elevations. The facets buried under the new snow are widespread across the region and remain weak.
  • Before this storm, the snowpack was weak and shallow. Numerous rocks, trees, stumps, and other obstacles existed on the surface or just below the surface. These obstacles remain close enough to the surface to hit and would increase the consequence of getting caught in an avalanche.

 

 

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