Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

New snow and wind are likely creating unstable avalanche conditions in areas where blowing snow has accumulated.  Additionally, new snow loading on top of an already weak snowpack may create unstable avalanche conditions in wind sheltered areas. Exercise caution near or below slopes where blowing snow is accumulating, snow surface cracking or audible collapse is occurring, or recent avalanches have occurred.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Blowing and drifting snow are expected to accumulate into wind slabs mainly on NW-N-NE-E aspects in above treeline and near treeline areas. Avalanche size up to D2 is possible, especially as wind slabs continue to grow in size through the day with continued snowfall and SW to NW winds.

    Look for, identify, and consider avoiding slopes that are below cornice features, have pillow-like wind drifts in the upper portions, or have visible snow surface texturing from the wind. In some locations especially above 8,500', these wind slabs may be loading on top of an already weak snowpack. Where this is the case, it could be easy to trigger an avalanche that is wider and travels further than expected.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Early season snowfall that sat on the ground through the extended Nov 10 to Dec 5 dry spell became weak and sugary as it faceted and changed snow crystal type. This is a problem on NW-N-NE aspects, especially near and above 8,500' or so both above and below treeline. Generally, the higher in elevation you go and the more shaded the slope, the weaker the snowpack. It doesn't matter if slopes are treed or not.

    As snowfall continues today persistent slab avalanches will become a concern in these NW-N-NE aspect locations where new snow amounts start to reach or exceed 8 to 10 inches. Recent avalanches, snow surface cracking, snowpack collapse, audible "whumpf" sounds from the snowpack, and unstable snowpit test results are all indications that conditions in the immediate areas are dangerous. If these signs of instability are present in your location, pull back into conservative, less steep, simple terrain.

Avalanche Discussion

*  Prior to this storm, 1 to 3 feet of snow existed on NW-N-NE aspects with continuous snow cover starting above about 8,000-8,500 ft.  Below about 7,800'-8,000' was a mix of patchy snow cover and bare ground. Almost all SE-S-SW-W aspects were snow-free with continuous bare ground exposed.

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