Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 8 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

MODERATE avalanche danger will exist at all elevations throughout the forecast region due to wind slab and persistent slab avalanche problems.  Large destructive human triggered avalanches could be possible today. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Large wind slabs that formed during our last storm with up to 4 feet of snow and over 100mph winds exist on NW-N-NE-E-SE aspects in near and above treeline terrain.  These wind slabs will take time to adjust to the new load and gain strength.  Some of these wind slabs sit on top of old weak faceted snow layers that could allow for remote triggering, wide propagation, and large avalanches.  Strong to gale force winds will return today ahead of our next storm.  Another round of wind slab development will become possible as snow transport begins.

     

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Old weak faceted snow that was buried during our last storm cycle is showing signs of weakness in many areas of the forecast region.  These old near surface facets exists below 1.5 to 4' of recent storm snow.  Easy snowpack test failures along with widespread whumpfing and collapsing of the snowpack on this facet layer occurred yesterday in multiple areas.  Uncertainty exists as to how long this weak layer will last and if any avalanche activity has occurred.  This layer has been found in the 7000-9000' elevation range on NW-N-NE-E aspects.   

    Large destructive avalanches are possible today.  Remote triggering and wide propagation could occur.  Until more information is learned, terrain management and conservative decision making are essential.  Travel on slopes well under 30 degrees with no overhead hazards.  Whumpfing or collapsing of the snowpack would indicate that this layer is still weak and potentially reactive. 

Avalanche Discussion

*  Observations from Hidden Peak (West Shore area) showed widespread whumpfing and collapsing of the snowpack failing on the weak old faceted snow that is below the recent storm snow.  Consistent easy snowpack test results observed.  A large density change in the upper snowpack was observed up to high point of 8700'. 

*  Observations from Powderhouse Peak and Trimmer Peak ( Luther Pass area) and Andesite Peak (Donner Summit area) all showed similar conditions with whumpfing and collapsing of the snowpack on the old near surface facets.  Snowpack test results showed failure on the faceted layer.  Weaknesses were also found under the large density change within the storm snow.

*  At Incline Lake Peak (Mt. Rose area) some storm snow instabilities existed.  Weakness at the old snow surface was not as pronounced as in other areas.

*  Please let us know what you see out there!

Regions covered