Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

CONSIDERABLE avalanche danger for today in above treeline and near treeline areas due to a wind slab avalanche problem from increasing amounts of pre-storm blowing and drifting snow. Areas of MODERATE avalanche danger may exist as wind slabs form in wind exposed areas below treeline due to the strength of the winds. Numerous wind slab avalanches occurred yesterday and the avalanche problem will become more widespread today.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    If you see blowing and drifting snow, think unstable wind slabs. Mid slope and ridgetop winds are increasing again out of the S to SSW today with speeds of 45 to 70 mph expected today and 100 mph forecast for tonight. Unstable wind slabs existed yesterday and new ones will form on top of them today. Plenty of soft snow remains above 8,000' in most ridgetop areas to be drifted and deposited as new unstable wind slabs pre-storm today.

    With the S to SSW winds, wind slabs from either direct loading or cross-loading are expected in near and above treeline terrain on W-NW-N-NE-E-SE aspects above about 7,500' to 8,000'. Avalanche size is expected at D1.5 to D2. The potential exists for some wind slabs to form along below treeline ridges and spines due to the strength of the winds. Once new snow starts falling tonight, avalanche size and distribution is expected to further increase.

    Figure out where the wind slabs are and avoid them. Unstable wind slabs are likely on slopes where blowing and drifting snow is depositing, below cornices, and in areas were rounded bulges (wind pillows) exist on the upper to the middle portion of slopes. Increase your margin of safety in any place where these clues for unstable wind slabs exist.

Avalanche Discussion

Natural and human triggered wind slab avalanches were reported yesterday from Round Top (Carson Pass area), Red Lake Peak (Carson Pass area), and Grouse Rock (Ward Canyon area). All of these avalanches occurred in above treeline or near treeline terrain on N-NE-E aspects where S to SSW wind had drifted and deposited snow Wednesday night. These avalanches failed 6 to 18 inches deep in the snowpack.

The middle and bottom portions of the snowpack have continued to gain strength and are in good condition to handle new snow loading. Avalanches that occur today and tomorrow are expected to have snowpack failure occurring in the upper portion of the snowpack.

In recent days, a variety of surface crusts have been noted below 7,500' to 8,000' with softer surface snow above 8,000'.

Regions covered