Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

There remains a chance that a larger avalanche could be triggered today failing on one of a variety of weak layers buried 1 to 1.5 feet deep by the most recent snowfall. In addition, blowing and drifting snow is expected to continue today with the possibility of triggering a smaller avalanche of wind drifted snow near ridgelines. Avalanche danger will increase substantially tomorrow afternoon into Sunday.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    New persistent weak layers in the form of a facet/crust combo and/or surface hoar were buried on Jan 2 and an avalanche cycle occurred on Jan 3. No additional avalanches were reported yesterday. Unstable snowpit test results were reported from some but not all areas yesterday. Some of these test results were highly concerning. There remains a chance that you could trigger an avalanche 1 to 1.5 feet deep today on a wide range of aspects. Once we get through today, additional new snow loading on these weak layers will likely lead to another avalanche cycle occurring this weekend.

    Any avalanches that are triggered today may not be preceded by obvious signs of instability. Forgiving terrain choices with minimal down slope hazards such as rocks, cliffs, and terrain traps are recommended. Look for recent avalanche activity, cracking in the new storm snow, and whumpfing sounds.  Keep in mind that persistent slab avalanches often have wide propagation that challenges traditional "safe zones" within avalanche terrain.  

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Ridgetop winds out of the NE yesterday drifted minor amounts of snow along the ridgetops. NE winds are forecast to continue today and increase a bit in speed. Some blowing and drifting of snow will likely be visible today along the ridgetops. Expect to encounter small, shallow wind slabs today along the downwind side of ridgetop areas.

    Look for areas where blowing snow is actively occurring and for any areas of snow surface cracking.  Snow surface scouring may also help to determine which side of the ridgetop has the most recent wind slab formation. Small avalanche size is expected, but consider the consequences of being carried into or over downslope hazards.

    (1/4/2024) Obvious signs of ridgetop wind drifting in progress. Castle Peak, Donner Summit area, CA Photo: Public

Avalanche Discussion

More on our persistent slab avalanche problem:

The scope of the persistent slab problem has changed with weak layers higher up in the snowpack now the main concern and the problem is distributed across more aspects. The Jan 2 layers of crust/facet combo and/or buried surface hoar found 1 to 1.5 feet below the old snow surface are the layers to watch.

For much of the season, the persistent slab problem focused on faceted snow near the base of the snowpack. Substantial strength gains in the midpack and a deepening of the snowpack along the Sierra Crest have reduced concerns for deep weak layer failure until a major atmospheric river type storm with multiple inches of SWE returns to the forecast area. In the Carson Range along the eastern side of the forecast area where the snowpack has remained shallower and weaker, the situation is different and there remains a greater concern for deeper weak layer failure with incremental new snow loading over the next week or so.

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