Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Large and destructive avalanches continue to occur within our forecast region.  The recent storm snow is overloading our previous shallow and weak snowpack.  Strong winds will also continue to form large slabs of wind drifted snow.  Dangerous avalanche conditions will continue today.  Pay attention to the terrain around you and above you-avalanches could be triggered from long distances away from steeper slopes. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    The persistent slab avalanche cycle continues in our forecast area.  The Dec 1 persistent weak layer formed during our dry spell in the 2nd half of November and is now buried under 1.5 to 3+ feet of snow.  This layer has been reactive with whumpfing noises, collapsing of the snowpack, shooting cracks, and large avalanches every day since our recent storm cycle has begun last Thursday.  Large and destructive avalanches are expected to continue  today.  This persistent weak layer is mostly found on NW-N-NE-E aspects, but has also been found on other aspects in isolated areas.  Avalanches that have occurred with this weak layer have propagated wider than expected, wrapped around terrain features, traveled further downhill than expected, and have been remotely triggered from far distances away.

    Clear signs of instability have been present everyday:  recent avalanche activity, shooting cracks, collapsing of the snowpack, and whumpfing noises.  The only effective way to deal with a persistent slab avalanche problem is by terrain management.  Back off steep terrain and ride slopes less than 30° in steepness with nothing steep above or adjacent to you.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    Additional snow with continued strong to gale force Southwest winds will further build out wind slabs on NW-N-NE-E-SE aspects in near and above treeline areas.  Large wind slabs and cornices exist and have not had the time to fully bond to the existing snowpack and gain strength.  These wind slab avalanches could run longer than expected and also step down to the deeper Dec 1 persistent weak layer causing larger and wider avalanches.

    Look for blowing snow, large cornices above a slope, wind pillows, and drifted snow to help evaluate where wind slabs exist.  Choose travel routes that avoid steep wind loaded slopes and areas below large cornices.  Cautious route-finding focusing on lower-angle terrain not connected to steeper terrain can help avoid both avalanche problems today. 

    (12/4/2022)

    Natural wind slab avalanche most likely due to cornice collapse.  Mid slope crown lines and propagation indicate that the wind slab stepped down to the Dec 1 persistent weak layer.

    Photo: Steve Reynaud

Avalanche Discussion

  • Avalanches and signs of instability continue to be reported throughout the forecast region.  Check out our observations page.
  • The facets buried under the new snow are widespread across the region on NW-N-NE-E aspects 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.

Regioni coperte