Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Alpine
1 · Low
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 13 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Near and below treeline NW-N-NE aspects still hold MODERATE avalanche danger on slopes steeper than 32 degrees because persistent slabs still remain in those areas.

Human triggered avalanches remain possible. Barely covered rocks, logs, stumps and other obstacles would increase the consequences of any avalanches that do occur.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    The near and below treeline NW-N-NE aspects still hold persistent slabs. In some areas the myriad of anchors/obstacles poking through the snowpack have kept these slabs small. In some areas these slabs have become more difficult to trigger. However, in most places data and observations continue to indicate that the additional weight of a person on top of the slope can break the weak layer (Dec 7th facets) and that the resulting fracture can still travel along that weak layer. Human triggered persistent slabs avalanches remain possible. 

    Any of these avalanches that do occur would drag a person through rocks, stumps, trees, and other obstacles because of the shallow snowpack and the fact that the near and below treeline terrain holds the most unstable snow as well as the greatest number of obstacles.

Avalanche Discussion

We did not receive or make any observations yesterday. Data and observations from earlier this week show that the Dec. 7th facet layer still exists in near and below treeline terrain on the northerly aspects. The data also indicates that this layer remains weak. As persistent weak layers like this one gain strength, they strengthen sporadically with some areas showing no signs of instability while adjacent areas remain unstable and easy to trigger. This process leads to a great deal of variability on all scales and uncertainty about which slopes or even which parts of the same slope remain unstable. Recent observations seem to indicate some of this variability. Tests in some areas indicate that fractures will not travel along the persistent weak layer. In other areas the same tests indicate that fractures can still travel along the Dec. 7th facets, and in some places the additional weight of a person on the slope can still break this layer and trigger a collapse that propagates along this layer.

The weak and shallow snowpack will not support a person or snowmobile enough to prevent collisions with all of the barely covered rocks, stumps, logs, and other hard immobile objects. Collisions with these obstacles could easily break equipment and injure people.  

Regions covered