Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Rapid new snow loading, drifting snow from gale force winds, and the stressing of older weak layers within the existing snowpack will create very dangerous avalanche conditions today. Avoid travel in, below, or adjacent to avalanche terrain. A rapid increase to HIGH avalanche danger will occur for all elevations today.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    There are several weak layers within the existing snowpack ranging from the Dec 11 PWL to buried surface hoar that are expected to be stressed to the point of failure today under rapid new snow loading. Persistent slab avalanches failing within the old snow are expected to have wide propagation and could be rather large and destructive today. Avalanches could be triggered from low angle areas near the bottom of a slope or from the side on an adjacent lower angle slope. Persistent slab avalanches are most likely today near treeline or below treeline on W-NW-N-NE-E aspects and to a lesser extent above treeline as well.

    While avoiding avalanche terrain today, keep well away from avalanche runout zones and pre-plan for how you are going to avoid avalanche terrain when poor visibility obscures the view of the terrain around you. Keep in mind that instability will rapidly rise as the day progresses and how that may affect a return route.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1

    Rapid new snow loading combined with gale force SW winds over ridgetops will create widespread areas of drifting snow deposits and new wind slabs in lee areas.  Wind slab avalanches are most likely to occur today above treeline and near treeline on NW-N-NE-E-SE aspects but could occur in any areas where drifting snow is deposited.

    Give cornice areas a wide berth. Ridgetop travel that avoids avalanche terrain could be difficult today due to gale force winds and poor visibiity. Keep in mind that instability will rapidly rise as the day progresses.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    High intensity snowfall today is expected to create unstable layers within the new snow. Avalanches failing on these layers could occur in wind protected areas below treeline on any aspect. Don't expect "in the trees" to be a safe place from avalanches today. Persistent slab and storm slab avalanches are a good bet below treeline today. Avoid avalanche terrain.

Avalanche Discussion

* The Dec 11 PWL gained some strength since the last storm but an overall poor snowpack structure remains. Recent snowpit data from around the forecast area indicates that this layer will likely become unstable again today under rapid new snow loading.

* Surface hoar buried a few inches below the old snow surface has been reported from some locations.

Regions covered