Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
1 · Low
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Avalanche danger remains LOW for most areas today. In areas where rain falls on the snowpack, pockets of MODERATE danger could form on NW-N-NE-E aspects on slopes steeper than 37 degrees due to the possibility of loose wet avalanches.

The avalanche danger will increase tonight and tomorrow as a strong winter storm brings wind, some rain, and 1-2 ft of snow above 7000 ft. The new load on top of the already weak snowpack should cause the avalanche danger to reach HIGH meaning that natural and human triggered avalanches will become very likely tonight and tomorrow. Travel in and around avalanche terrain is not recommended tonight or during the day tomorrow.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Natural and human triggered wet loose avalanches could become possible again today in places where where light rain falls on the snowpack. Near and below treeline NW-N-NE aspects below 8,000 to 9,500' that already hold wet snow and areas where water saturates some of the near surface facet layers will hold the greatest potential for these wet loose slides. Still these wet snow problems could occur on any snow covered slope that receives rain today. Steeper slope angles upwards of 37 degrees may be necessary for avalanches to initiate.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    During the day today persistent slabs avalanches should remain unlikely since there is not much new load above them. However, as new snow and wind impact the forecast area tonight and tomorrow, this avalanche problem will become a serious threat. For the last several weeks the snowpack has gotten weaker and weaker and the only ingredient missing from the avalanche recipe has been a thick cohesive slab layer. This storm will provide that slab layer in the form of 1-2 ft. of dense storm slabs and wind slabs. Data indicates that the current snowpack will not support this load. Natural and human triggered avalanches will become very likely overnight and tomorrow. The size and extent of these avalanches will also increase as the snow accumulates. This is an unusual winter with a snowpack more like a CO pack than a Tahoe pack. Don't let old habits or "powder-fever" dictate decisions tomorrow. 

Avalanche Discussion

Yesterday observations on Andesite Peak, near Emerald Bay, and at Mt. Rose, all showed wet unconsolidated snow on the surface. In all three of these areas small wet loose slides involving this surface snow occurred (see photos below). On Andesite Peak and at Mt. Rose below the wet surface snow, the snowpack still consists of several layers of very weak facetted snow. Tests and data indicated that the snowpack in both these places would not support the new snow load expected to arrive over the next 36 hours. All across the forecast area data and observations have shown similar weakness where ever snow exists.

Regions covered