Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

People will likely trigger dangerous avalanches today. These could happen on open slopes where wind-blown snow has piled up or in more sheltered areas where buried weak layers exist under the new snow. In some places, both problems may exist! If you see any signs of unstable snow, like recent avalanches, cracking, or collapsing, or doubt a slope, go ahead and stick to more conservative terrain to reduce your exposure. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Yesterday afternoon, snowmobilers triggered a small avalanche while riding on a low-angle road. Around the same time, skiers caused shooting cracks that failed on buried surface hoar and weak snow near crusts. Observers have reported these buried weak layers in most areas around the region. Some natural failures likely occurred last evening during the peak of the storm. While the natural activity may have subsided with the storm's end, people will likely still trigger avalanches on these persistent weak layers today. Since one to two feet of snow covers these layers, avalanches could easily involve enough snow to bury or injure a person.  In some places near ridges, wind-loading could have piled even more snow on top of these weak layers, giving rise to even larger avalanches.

    Clues like recent avalanches, snow surface cracking, snowpack collapse, or whumpfing sounds indicate unstable, persistent slabs. People can trigger persistent slab avalanches from above, below, or to the side of a slope, and they often break wider than expected. If you see any signs of unstable snow or have any doubt about a slope, play it safe, assume it is unstable, and stick to low-angle, non-avalanche terrain not connected to steeper areas above or beside it.

    (1/6/2024) Snowmobilers remotely triggered this small avalanche on the shoulder of Yuba Pass Road at 7500 feet. It likely failed on a buried persistent weak layer.

  • Wind Slabs

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

    People began to trigger wind slab failures on test slopes yesterday afternoon as strong SW winds deposited slabs of wind-blown snow during the storm. Last night, the winds shifted to the NE and moved snow back across the ridges, forming new wind slabs on different aspects. These shifting winds have likely scoured wind slabs away from some of the upper-elevation slopes that got loaded yesterday but may have left some of yesterday's mid and lower-elevation wind slabs in place. Expect to find a mix of scoured and wind-loaded areas in any exposed areas today. Triggering wind slab avalanches remains likely. Larger and more widespread wind slabs will exist in near and above treeline terrain, but some wind slabs may also linger in open areas below treeline due to the strength of yesterday's wind.

    Blowing snow, cornices above a slope, and wind-created surface textures can help determine where wind slabs exist. Patterns of snow surface scouring can also help identify where wind-blown snow may accumulate. The shifting winds will make locating wind slabs harder today so careful evaluation of these clues will be necessary. Exercise increased caution today around wind-loaded areas, especially if there are signs that any of the above-mentioned persistent weak layers are present in the area. 

    (1/6/2024)

    A ski kick triggered this small wind slab in near treeline terrain on Andesite Ridge in the early part of yesterday's storm.

    Photo: SAC

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 4 inches 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.

Regions covered