Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Highlights

LOW avalanche danger will continue through the day today. Normal caution is advised. Avalanche danger will begin to increase tonight following the onset of snowfall as new wind slabs begin to form in lee areas.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    A period of strong SW winds occurred during the day yesterday with minimal amounts of snow on the ground available for wind transport. New wind slab formation is not expected to have occurred on any type of widespread scale, but is not impossible in an isolated location, somewhere within the forecast area. Keep an eye out for signs of recent wind loading such as human triggered cracking, wind pillows, or new cornice formation on NW-N-NE-E-SE aspects in near or above treeline terrain.

    Following the onset of snowfall with the approaching storm, new wind slabs are expected to form on a more widespread scale tonight in near and above treeline areas on NW-N-NE-E-SE aspects.

     

Avalanche Discussion

Observations made yesterday on the N side of Ellis Peak (Blackwood Canyon area) between 7,000' and 8,500' matched well with other recent observations made along the northern portion of the Sierra Crest on N aspects at similar elevation. The problematic facet layer was present near the bottom of the snowpack on top of basal ice (see photo). Snowpit tests indicated that until significant new loading occurred, triggering weak layer failure remains unlikely. However as in other locations, snowpit tests indicated that once weak layer failure is initiated, propagation is likely to occur along this weak layer deep in the snowpack.

Minor amounts of blowing snow were observed on the N side of Ellis Peak in areas that typically receive wind loading, but no new wind slabs of any significant size were observed.

With a series of storm systems lined up and expected to impact the forecast area, start thinking about how this will potentially affect the facet layer that has been a focus of snowpack monitoring so far this season. There are no guarantees, but day to day snowpit data continues to indicate that this weak layer could become problematic under future loading conditions. Over the next week it is expected that new snow will significantly increase the load on this weak layer. The potential exists for avalanche activity to occur on this layer deep in the snowpack. Again there are no guarantees as to if this will come to fruition. The point is that this is the setup for a persistent deep slab avalanche problem, requiring a very different type of terrain management approach than when dealing with the typical Sierra storm slabs and wind slabs. Have a look at the Avalanche Problem Toolbox and read up on what to expect, how it differs from assessing and managing wind and storm slabs, and how to manage a persistent deep slab problem.

This facet layer exists near the base of the snowpack, usually on top of a ground level ice layer. This weak layer is found on N aspects along the Sierra Crest above about 8,300' and in the Mount Rose area above about about 9,300'.

Regions covered