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

Isolated pockets of moderate avalanche danger will exist throughout the forecast area today.  Wind slabs and persistent slabs remain a lingering concern on all aspects above treeline and NW-N-NE aspects near treeline and below treeline.  Low danger exists for all other areas.  Human triggered avalanches will remain possible in isolated terrain.  Evaluate snow and terrain carefully and use proper travel techniques to help mitigate risk.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    The moderate to strong NE winds have been creating reactive wind slabs throughout the forecast area above treeline.  We had 2 reports of wind slab avalanches from yesterday in near and above treeline terrain that was actively being wind loaded.  The last few days of moderate to strong NE winds have redistributed snow back to SE-S-SW-W-NW aspects.  In complex terrain, many features have been top loaded and cross loaded making for potential wind slabs on all aspects near and above treeline.  The winds will shift today from the NE to the NW and decrease bringing an end to the wind slab development.  Below average cold temperatures could slow the bonding process of these wind slabs making them a concern for today.  Look for cornice formation, snow surface scouring, and wind pillows for clues as to where wind slabs may exist.  

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Near crust facets that have developed near the 12/10 and 12/13 rain crusts are still showing unstable results during snowpack tests.  The 12/10 rain crust has shown weakness mainly in the southern half of the forecast region and the 12/13 rain crust has been more widespread.  While it remains unlikely to trigger an avalanche on this layer if a user could find the right combination of weak layer with slab on top it remains possible.  On many exposed areas on N-NE-E aspects near and above treeline, the surface snow has been scoured by the recent winds.

    The buried surface hoar layer that was responsible for avalanches this past Sunday is now thought to be unreactive in most areas.  The last few days of observation work show the distribution of this weak layer throughout the forecast area appears to be limited.  Where is has been found, it has collapsed causing less concern as a weak layer. 

Avalanche Discussion

An avalanche was reported from Incline Lake Peak yesterday.  This avalanche occurred on a 40 degree slope angle with an E/NE aspect.  It was 50' wide and ran downslope for 400'.  There were strong N winds in the morning hours that were cross loading this gully feature that was thought to create the wind slab that avalanched.  The trigger is unknown but with no signs of tracks in the area this could be a natural avalanche.  This avalanche was large enough to injure, bury or kill a backcountry user.

A smaller wind slab avalanche was reported on the SW upper face of Castle Peak.  This was skier triggered and this slope was being actively wind loaded by the moderate to strong NE winds yesterday.

Observations from Grouse Rocks (Ward Canyon) and Andesite Peak (Donner Summit) revealed weakness associated with the 12/13 rain crust.  Snowpack tests showed propagation was possible on this layer but no other signs of instability were noted.  Protected terrain near treeline and below still have unconsolidated surface snow with exposed areas above treeline being wind scoured.    

Regions covered