Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

MODERATE avalanche danger will continue in near and above treeline areas due to wind slabs. Storm slabs are becoming unlikely, with LOW avalanche danger in below treeline areas. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Strong SW winds yesterday began transporting snow and forming new wind slabs and cornices.  SW winds continued overnight and are forecasted to remain strong to gale force through today.  New unstable wind slabs are expected in near and above treeline terrain on NW-N-NE-E-SE aspects.  These wind slabs could be large enough to injure or bury a backcountry user. 

    Look for blowing snow, new cornice formation, and snow surface scouring as clues to where new wind slabs will exist.  Avoid travel below large cornices and steep wind loaded terrain.

     

     

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Buried surface hoar below the 12/6-12/8 storm snow has been responsible for 1 snowboarder triggered avalanche on Monday and thought to be responsible for a handful of natural avalanches near the end of the storm cycle on Sunday.  This weak layer has been found in isolated areas and is thought to have only been reactive in the Donner Summit area.  Continued snowpack tests and observations have found this layer to be gaining strength with stubborn to non-reactive snowpack test results in most areas sampled. 

    While isolated on a regional forecast scale, it’s not impossible that this weak layer and storm slab combination could still be encountered.  It has been found on Northerly aspects, above 8000', in below treeline, or wind protected near treeline terrain.  Even though this storm slab avalanche problem has become unlikely, safe travel protocols and good group decision making still apply.     

Avalanche Discussion

* Dec. 9 - Castle/Basin Peak Avalanche Incident Report

* Observations from the recent avalanche incident showed decomposing surface hoar gaining strength.  Snowpack tests showed stubborn to non-reactive results.

* Strong SW winds yesterday were transporting snow along the ridges above 8500'.  New wind slab and cornice formation were observed.

* A variety of crusts and wet snow exists on southerly aspects.  Cold winter snow can still be found on northerly aspects.

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