Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

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

In sintesi

Slabs of wind blown snow formed yesterday in wind exposed areas and continued to build overnight with light new snow and continued winds.  Wind slab avalanches could be triggered by backcountry users again today.  A persistent slab avalanche problem continues at higher elevations where weak snow exists at the base of the snowpack.  Look for signs of unstable snow and move away from areas of concern.  

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    A snowboarder triggered a wind slab avalanche and was injured in the Carson Pass area yesterday.  Wind speeds and drifting snow far exceeded expectations yesterday in many areas of the forecast region.  With some light amounts of new snow and continued strong winds overnight, a wind slab avalanche problem will continue today.  Wind slabs could easily be 1.5 to 2 feet deep or more in areas with efficient wind loading and available snow for transport.  Where these wind slabs have developed on top of near surface facets, avalanches could be triggered easier and break wider than expected.

    Look for continued blowing snow, new cornice development, wind pillows and snow surface clues as to where wind slabs have formed.  Our early season conditions make any avalanche involvement high consequence with all the rocks and obstacles present.

    (12/27/2023)

    Snowboarder triggered wind slab avalanche.  The crown at the very top of the face and debris pile at bottom.  Red Lake Peak, Carson Pass area.

  • Persistent Slabs

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

    A weak snowpack structure continues to exist in higher elevation areas of the forecast region.  Areas above around 8500' have weak faceted snow near the ground  buried underneath 1 to 3 feet of snow.  No avalanches have been reported on these weak layers up to this point with decreasing signs of instabilities.  Future storms will reload and retest these weak layers.  Avalanches remain unlikely at lower elevations where a stronger and more consolidated snowpack exists without this weak layer. 

    Obvious signs of instability are hard to come by these days without digging into the snow and looking at the layers.  To limit your exposure to this avalanche problem, you can recreate on non-avalanche terrain with no overhead hazard or pick areas and locations where this persistent slab avalanche problem does not exist.

Avalanche Discussion

Extended periods of clear weather and a shallow snowpack have left various weak layers on the cold, northerly aspects that do not see much sun this time of year. Facets exist near the bottom of the snowpack, on the surface, or near/between crusts. Recent warm weather has allowed the weak, faceted (sugary) snow to start clumping together in some areas. In other places, the weak layers remain dry and loose. In general, the snowpack gets weaker as elevation increases and you move east of the Sierra Crest. Our shallow snowpack is highly variable from one location to the next and throughout the forecast region. This persistent slab problem may linger for some time and could reactivate in future storms.

Warm weather and fog have left crusts on the snow surface up to around 8,300 ft, potentially higher in some areas.

The snowpack has become more usable, especially above 7,500 ft. There are still rocks to hit and open creeks to deal with, but not as many as there were before this last storm.

Regioni coperte