Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Moderate avalanche danger exists on NW-N-NE-E-SE aspects, on slopes steeper than 32 degrees, at all elevations, due to wind slabs and persistent slabs.  On S-SW-W aspects at all elevations, low avalanche danger exists.  Human triggered avalanches are possible today.  Evaluate snow and terrain carefully, identify features of concern. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Sensitive and reactive wind slabs formed yesterday in near and above treeline terrain throughout the forecast area.  These winds slabs were 8'' to 2' in size and were failing on a density change within the new storm snow.  These wind slab avalanches were noted in several areas to have wide propagation and very poor bonding to the snow below and could be sensitive throughout today.

    This problem exists in near and above treeline terrain on NW-N-NE-E and potentially SE aspects.  Look for evidence of previous blowing snow, cornice formation, wind pillows, and snow surface scouring to help identify where wind slabs exist. 

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    Persistent weak layers in the form of buried surface hoar exist throughout the forecast region in some areas on N-NE-E aspects near and below treeline and possibly on NW and SE aspects.  These weak layers are now buried anywhere from 1.5' to 4' deep in the snowpack.  We have experienced a large avalanche cycle on these weak layers over the last 2 weeks.  Many of the suspect slopes have already avalanched, or the surface hoar has been compressed or collapsed and has started to gain strength.  With that said, observations are still finding these layers intact with reactive snowpack tests and we have had recent avalanches associated with these layers during our latest storm cycle.

    The recent rain and heavy snow storms have just added additional weight and stress to these weak layers.  Large destructive avalanches, severe consequences, and remote triggering continue to remain possible today.    

Avalanche Discussion

Observations from Andesite Peak (Donner Summit area) showed 6'' of heavy new storm snow in this area.  Sensitive wind slabs formed near and above treeline and intentionally human triggered avalanches were propagating wide distances.  These wind slabs were failing on a density change within the storm snow and were 8'' to 2' deep.  Buried surface hoar was found in this area intact and a small avalanche below treeline was thought to be caused by this weak layer.  Rain was observed up to 8000' in the early afternoon.

On Powderhouse Peak (Luther Pass areas) similar conditions existed.  Storm slabs and wind slabs were easily failing on the same storm density change.  Storm slabs in protected areas 6'' deep were reactive as well as wind slabs near ridges.  Snow levels hovered around 7700' in the morning and climbed higher into the afternoon.

Regions covered