Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Rapid warming conditions and snow surface melt will raise concern for a variety of wet snow avalanche problems today including loose wet, wet slab, and cornice collapse. MODERATE avalanche danger is expected to form quickly today for all elevations, further increasing to CONSIDERABLE danger during the afternoon hours.

Avalanche problems

  • Glide Cracks

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    0

    With above average air temperatures and a wind shift to the W, cornices will rapidly warm and melt today. Natural or human triggered cornice collapse is an elevated concern today. Large to very large cornice chunks may fall and tumble down the slopes below. These cornices chunks have destructive potential on their own. Falling cornices may also trigger loose wet or wet slab avalanches, increasing the destructive potential further.

    Stay well back from abrupt edges on ridgelines and out from under cornices, especially if you can see or hear meltwater dripping from the cornice.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Inversion conditions kept air temperatures at the mid slope and upper elevations above freezing last night but skies were clear. A decent but very superficial snow surface refreeze is expected to have occurred last night from the radiational cooling of the snowpack. This refreeze is not expected to be as strong as what occurred the previous two nights. Strong mid April sunshine will rapidly melt the 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.

    Anticipate rapid melt rates today, faster than what occurred on Monday and Tuesday. Avoid steep terrain in areas where the surface crust is no longer supportable. E-SE-S aspects will melt the quickest, followed by varied rates on 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

* A report was received of a large natural avalanche, possibly a wet slab that may have occurred Monday in the vicinity of Mt. Price (Desolation Wilderness area) on a NE aspect with the crown at mid slope. The avalanche was seen from afar. No other details are known.

* Diurnal melt-freeze conditions exist on 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