Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 10 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Considerable avalanche danger exists at all elevations throughout the forecast area.  Dangerous avalanche conditions continue due to wind slabs, storm slabs, and deep slab avalanche problems.  Human triggered avalanches are likely and natural avalanches are possible today.   

Problemi valanghivi

  • Wind Slabs

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

    Wind slabs will continue to be a problem with additional new snow and wind throughout today.  These wind slabs will be most problematic on NW-N-NE-E-SE aspects and potentially S aspects as the winds shift towards the West today.  Natural wind slab avalanches occurred yesterday and that is expected to continue through today.

    Look for areas of blowing snow, cornice formation, and wind pillows to identify where wind loading is occurring and subsequent wind slab development.  Avoid wind loaded terrain and avalanche run out zones below wind loaded terrain.

  • Loose Dry

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

    Total storm snow this week is 4+ feet throughout the forecast region above 7000'.  Weaknesses within this recent storm snow will continue to be a problem for today.   There have been large fluctuations in temperatures throughout this storm cycle that have caused some areas to have an "upside down" structure.   These storm slabs will be in mostly protected areas in below treeline and near treeline terrain on all aspects.

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    3

    Deep slab avalanches continue to be possible on weaknesses within the old snow that is buried anywhere from 4 to 8+ feet deep below the snow surface.  Layers of concern are developed near crust facets that are near the Dec. 15 rain crust and old near surface facets at the base of the storm snow.  Any avalanches that either initially fail on or step down to these weak layers will be large and destructive.  This deep slab avalanche problem is possible on W-NW-N-NE-E aspects at all elevations.  

Avalanche Discussion

Observations were made and received yesterday from Andesite Ridge (Donner Summit area) and Waterhouse Peak (Luther Pass area).  Several natural wind slab avalanches were observed in the Andesite Ridge area.  These avalanches occurred on N-NE-E aspects, 35 degrees or steeper, in near treeline terrain, with crowns up to 3' deep.  These avalanches were failing within the recent storm snow.  There was a noticeable density change within the more recent storm snow with a upside down structure.  On Waterhouse Peak, cracking and whumpfing was observed throughout the area.  Snow level was around 7000' mid morning with 2''/hour snow accumulation throughout the day.  A PST on the near crust facets near the Dec. 15 rain crust, now buried 3 to 4 feet deep, indicated that this layer is still capable of producing avalanches.

Regioni coperte