Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

Shifting winds over the last 24 hours are expected to have deposited slabs of wind drifted snow in a variety of areas. Lingering instability may also exist within the new snow in wind protected areas. Backcountry travelers could trigger very large avalanches today.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3

    Winds were out of the SW yesterday, shifting to the NE last night. Last night's NE winds were strong. Expect to encounter a mix of wind scoured and wind loaded areas in near treeline and above treeline terrain today. Large, thick slabs of wind drifted snow could be encountered on any aspect today with substantial variation from one location to another around the forecast area. Wind slabs are most widespread in near treeline and above treeline terrain and may also exist to a lesser extent in below treeline terrain.  Wind slab avalanches triggered today by backcountry travelers could be very large.

    Consider intentionally choosing terrain today that is not capable of producing large wind slab avalanches. Slopes that appear filled in by wind drifted snow are highly suspect. Use clues such as the most recently formed wind drifts, cornices, and snow surface texture to identify areas of concern.

    (12/30/2022)

    Natural wind slab avalanche, cornice fall triggered, Wildflower Ridge, NE aspect at 7,800'. Donner Summit, CA

    Photo: Steve Reynaud

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Snowfall rates were impressive yesterday at 3 to 7 inches per hour. Snow was accumulating faster than it could bond. Substantial storm slab instability was observed yesterday in wind protected areas below treeline, failing deep within the new snow. With the high intensity snowfall having ended, this problem should be less widespread today, but lingering instability is a concern.

    Snow surface cracking created while breaking trail is an indication of unstable snow. Following in someone else's track provides very limited opportunity to identify the presence of unstable storm slabs. Get out of existing tracks from time to time and observe if you create snow surface cracking. If snow surface cracking is occurring, steer clear of convexities and areas of steeper terrain.

    (12/31/2022)

    Storm slab avalanche the N side on Rubicon Peak. The small size of this avalanche was due to terrain limitations with only a very small section of slope over 30 degrees in slope angle where the avalanche could physically occur.

Avalanche Discussion

Poor visibility has limited avalanche occurrence data over the past 48 hours. We do know that:

  • Natural wind slab avalanches and natural wet loose avalanches at least to size D2 were observed during this storm. Some wind slabs avalanches had wide propagation with cornice collapse as a common trigger.
  • Widespread storm slab instability was observed yesterday in wind protected areas below treeline on Hidden and Rubicon Peaks on the West Shore of Lake Tahoe.
  • A thick layer of rain soaked snow exists below the recent storm snow in nearly all areas below about 8,500' to 9,000'. It will take several days for this layer to fully refreeze.
  • Creek flows are decreasing rapidly but may continue to carry substantial amounts of water today.

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