Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 6 years ago.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

Highlights

A powerful winter storm is expected to bring multiple feet of new snow with gale force winds over the next 2 days.  This new snow will be loading a shallow and generally weak snowpack.  Large and destructive avalanches involving the new snow and the existing snowpack could occur.  EXTREME avalanche danger exists for the SAC forecast region.  Travel in or near avalanche terrain is not recommended and should be avoided.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    Persistent slab avalanches could be large, with wide propagation, and fail within the existing snowpack.  Multiple layers of concern exist in our current snowpack that have the potential for deeper and larger avalanche activity.  Buried surface hoar, near crust facets, and a deep persistent weak layer-any of these concerns could make for larger and wider avalanche activity today.  In areas where a shallow and weak snowpack has existed for most of the season, like Carson and Ebbetts pass along with areas east of the Sierra Crest, avalanches have the potential to be large, wide, and involve most of the existing snowpack. 

    Avalanches have the potential to run long distances and be very large.  Travel in or near avalanche terrain is not recommended. 

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Certain
    Size
    2–3

    Multiple feet of new snow with gale force winds will create large to very large wind slabs on NW-N-NE-E-SE aspects in near and above treeline areas.  Cornices are expected to build out during this storm cycle and be very large and weak.  Wind slab avalanches could run long distances into below treeline areas and lower angle terrain.  Any terrain below large cornices or wind loaded slopes is suspect.  Natural wind slab avalanches will be almost certain today.  

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Storm slab avalanches could occur on all aspects in near and below treeline areas.  Rapid loading with snowfall rates up to 4-5''/hour and any temperatures fluctuations throughout the day could cause storm slab avalanches.  Storm slab avalanches could involve part or all of the recent storm snow. 

Avalanche Discussion

* Small wind slab avalanches and blowing snow were reported from multiple locations yesterday.

* The Dec 11 PWL in the lower portion of the snowpack could cause a deep slab avalanche problem if this winter storm performs as forecasted.

* With numerous weak layers in our current snowpack from the now buried surface hoar layers, near crust facets in the upper snowpack, and the lingering Dec 11 PWL, the existing snowpack is in poor condition to handle a major new snow load.

Regions covered