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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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

MODERATE avalanche danger continues for our area.  A persistent slab avalanche problem remains a concern in below and near treeline areas.  Increased winds overnight will make unstable wind slabs in near and above treeline terrain.  Human triggered avalanches remain possible today.  

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    The Dec. 11 persistent weak layer is buried under about 1 foot of snow and has been a concern for over a week.  Just as it took time for this layer to facet and weaken, it has taken time for the weak layer to adjust to the current snow load and gain some strength.  Yesterday marks the first day without reports of active whumpfing on this layer from the forecast region.  Unfortunately, reports of unstable snowpack test results did come in and large variability continues from one area to the next.  This weak layer exists on W-NW-N-NE-E aspects in below and near treeline areas.

    Whumpfing sounds, cracking, and/or unstable snowpack test results could indicate that this weak layer is still active in your specific area.  Limiting exposure to avalanche terrain by using only sub 30 degree angle slopes without steeper connected slopes above or to the side is the easy way to manage this avalanche problem.  

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    SW winds increased overnight into the strong to gale force range at higher elevation.  Snow transport is expected with small unstable wind slabs forming last night on NW-N-NE-E-SE aspects in near and above treeline areas.  Winds will shift towards the NW today and then to the E tonight remaining gusty in near and above treeline areas and possibly transporting snow to other aspects.  Avoid areas below new cornice formation and newly formed wind pillows and drifts.   

Avalanche Discussion

* Unstable snowpack test results were reported from the Castle Peak area yesterday on the Dec 11 persistent weak layer.  Other reported snowpack tests from Incline Lake Peak (Mt. Rose area) and Shirley Canyon (Squaw Valley area), did not show unstable results.  No whumpfing, cracking, or other signs of instabilities were reported yesterday.

* Increasing SW winds were observed yesterday with light snow transport reported starting in the early afternoon.

* Surface hoar was reported from lower elevation areas not influenced by the recent temperature inversions.

Regions covered