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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Highlights

MODERATE avalanche danger exists today for all aspects both above and below treeline on slopes 35 degrees and steeper due to expected poor snow surface refreeze last night and rain on snow this afternoon. Increasingly hazardous avalanche conditions are expected this evening into tomorrow as wind slabs begin to form in near and above treeline areas on NW-N-NE-E-SE aspects.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    A poor snow surface refreeze is expected to have occurred last night in areas below 9,000' to 9,500'. Warm overnight air temperatures will have kept snow surface refreeze reliant on radiational cooling. In open areas below 9,000', snow surface refreeze that did occur is expected to be thin and superficial. Little to no snow surface refreeze is expected to have occurred in treed areas where the forest canopy inhibits significant radiational cooling. Rain on snow expected this afternoon will add additional free water to the snowpack. In many areas below 7,500' to 8,000', recent melt has established free water drainage from the snowpack and today's rain will drain from the snowpack fairly easily. In the 8,000' to 9,000' zone where free water drainage is not as well established, more loose wet instability could occur during rain on snow this afternoon, especially on W-NW-N-NE-E aspects.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    Strong to gale force SW winds and up to a few inches of new snow beginning to accumulate above 8,000' late today and tonight will start the formation of small wind slabs in near treeline and above treeline terrain. This avalanche problem is expected to become increasingly widespread on NW-N-NE-E-SE aspects above 7,000' to 8,000' as wind slabs build over the course of this storm cycle. Use clues such as signs of avalanche activity from the last storm cycle, cornice formations, wind pillows below ridgelines, and blowing snow to determine the location of potentially unstable wind slabs.

Avalanche Discussion

Observations made yesterday on Ralston Peak (Echo Summit area) and while traversing the Sierra Crest between Sugar Bowl and Squaw Valley revealed differing degrees of snow surface melt from one area to another. Once the snow surface started to melt around 10:30 to 11 am, some areas became marginally skier supportable by mid day while other areas remain highly supportable, especially above 8,000'. By late in the afternoon, unsupportable deep wet snow was widespread on E-SE-S-SW-W aspects below 7,800'. In these mid and low elevation areas, well established free water drainage from the snowpack kept loose wet instability to a minimum.

Regions covered