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

Early this morning, avalanche danger is LOW for all elevations and aspects. As the day progresses, areas of MODERATE danger will form on all aspects at all elevations on slopes 37 degrees and steeper in response to daytime warming. Small human triggered loose wet avalanches will become possible.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    A decent snow surface refreeze is expected to have occurred last night due to air temperatures near or below freezing and radiational cooling of the upper snowpack mostly uninhibited by cloud cover. As daytime warming progresses, the snow surface will transition from frozen and supportable to melt phase with developing wet snow instability. Human triggered loose wet avalanches will become possible from late morning onward, especially during the afternoon and evening hours. Most areas of instability will exist on E-SE-S-SW-W aspects, spreading to include areas on NW-N-NE aspects later in the day. Above treeline areas with exposure to wind will experience convective cooling of the snow surface and slower melt rates than wind sheltered areas near treeline and below treeline. With many previous melt-freeze cycles and previous rain events having already occurred this winter and spring, free water drainage from the snowpack is well established. This is expected to keep loose wet avalanche activity limited to human triggered avalanches that are relatively small in size.

Avalanche Discussion

Observations made yesterday on Castle Peak (Donner Summit area) indicated that a decent snow surface refreeze occurred in this area Friday night. In above treeline areas, moderate to strong southwest winds provided convective cooling of the snow surface which greatly slowed the rate of snow surface melt. In wind protected areas near treeline and below treeline, snow surface melt occurred rapidly. At 12:30 pm, ankle deep boot penetration was noted in above treeline terrain at 8,500' on a wind exposed SW aspect. Much deeper boot penetration could easily be found in wind sheltered areas at that same time. At 12:45 pm, unsupportable snow surface conditions were observed on wind protected S aspects at treeline at 8,000'. Overall, the rate of snow surface melt and development of surface wet snow instability was greatly influenced by exposure to wind in any given location (photo, more info).

Regions covered