Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Highlights

The avalanche danger will remain LOW until the precipitation starts to fall. Once the snow begins accumulating the avalanche danger will increase quickly and could reach HIGH on slopes steeper than 32 degrees during the night. Natural avalanches will become likely tonight and early tomorrow morning. Wind slab, storm slab, and deep persistent slab avalanches will all become problems during the next 24 hours. Travel in and around avalanche terrain is not recommended during the storm.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    3

    Triggering a persistent slab avalanche will remain unlikely until new snow starts to accumulate this evening and during the night. At some point the weight of the new snow will likely overload this weak layer resulting in destructive deep persistent slab avalanches that break near the ground. NW-N-NE aspects above 9000-9500 ft. where this persistent weak layer of loose sugary snow (facets) still lingers represent the best places to trigger deep persistent slab avalanches. Sometime tonight natural and human triggered deep persistent slab avalanches will become likely.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    New snow and wind during this storm will form wind slabs on wind-loaded NW-N-NE-E-SE aspects. Due to the strength of the winds associated with this storm wind slabs may form at all elevations and in areas that typically remain sheltered from the winds. These winds slabs may start forming today, but triggering a significant wind slab will remain unlikely until more snow accumulates tonight. During the night natural and human triggered wind slab avalanches will become likely.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Changing conditions during the storm will create weaknesses within the storm snow that could result in storm slab avalanche activity. Like the other avalanche problems, storm slabs will remain unlikely until enough snow accumulates on top of the current snowpack. Sometime during the night natural storm slab avalanches could become possible and human-triggered storm slabs could become likely in areas with enough new snow on them.

Avalanche Discussion

Observations from the Mt. Rose backcountry yesterday continue to show a persistent weak layer near the base of the snowpack on NW-N-NE aspects above 9000-9500 ft. Tests on this layer in the Relay Peak area and on Tamarack Peak indicated that once this layer breaks the resulting fractures can travel along the weak layer. While data around the forecast area indicates a currently stable snowpack, the same data also points to a snowpack that will not be able to support the additional snow load that the forecasted storm is supposed to deliver over the next 24 hours.

Snow covered mountains, improving weather, and fresh tracks tomorrow will make it easy to forget about the deep persistent slabs, wind slabs, and storm slabs that form during the night. Slopes that don't slide tonight will be problematic tomorrow especially in areas where the persistent weak layers exist. A slope breaking around a person and avalanching often represents the only warning that persistent slabs give people. For some advice on dealing with persistent slabs, wind slabs, and storm slabs check out this page.

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