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

Loose wet avalanche problems will develop quickly today in wind protected areas. Wet slab avalanches also warrant consideration. LOW avalanche danger very early this morning will increase to MODERATE avalanche danger as the morning progresses.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    A strong but superficial snow surface refreeze is expected to have occurred last night with clear skies and below freezing air temperatures. Strong mid April sunshine will rapidly melt the firm snow surface as the morning progresses. Once the surface crust melts away, deep wet snow prone to loose wet avalanches will exist. Avalanche size up to D2 is expected.

    While NE winds will keep the snow surface frozen at and near ridgetops for much of the day, rapid melt will occur just off of the ridgetops and on the slopes below. Don't be fooled by firm frozen surfaces on ridgetops or other wind exposed areas. Anticipate rapid melt rates on the slopes below. Avoid steep terrain in areas where the surface crust is no longer supportable. E-SE-S aspects will melt the quickest, followed by SW-W-NW-N-NE aspects.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Forecasting a wet slab avalanche is notoriously difficult. Too much uncertainty exists to assign a likelihood to this avalanche problem. The current snowpack structure may allow for the possibility of a wet slab avalanche to occur when meltwater percolates down to the March 24 buried surface hoar layer. This potential weak layer is located 1 to 2 feet below the snow surface on some open NW-N-NE-E aspects. Avalanche size is expected at D2.

    As long as there was a decent to strong overnight refreeze, timing and terrain choices to avoid deep wet snow and/or steep terrain could help avoid wet slab avalanches. Any time a weak to non-existent overnight refreeze occurs or later in the day when deep wet snow exists, all bets are off.

Avalanche Discussion

* Yesterday, even with a strong snow surface refreeze, snow surface melt occurred rapidly creating concerning amounts of deep wet snow on wind protected E-SE aspects by 9:30 to 11 am.

* Diurnal melt-freeze conditions exist all aspects.

* The March 24 buried surface hoar layer that is located 1-2 feet below the surface on some NW-N-NE-E aspects is being monitored as a potential weak layer for wet slab avalanches.

Regions covered