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

Human-triggered avalanches will be likely today in near and above treeline terrain due to a wind slab avalanche problem. The avalanche danger is CONSIDERABLE. Some loose dry avalanches may also be possible in more sheltered terrain. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    New wind slabs have formed on top of old wind slabs that rest on top of old weak surface snow. The largest wind slabs should lurk on NW-N-NE-E-SE aspects loaded by the SW winds in near and above treeline terrain. Smaller wind slabs are possible on NE wind-loaded W-SW-S aspects. In some cases, wind slabs may have crept into wind-exposed areas below treeline as well. While the best period for natural wind slab avalanches should have occurred during the night, human-triggered wind slab avalanches large enough to bury or injure a person will remain likely today. 

    Identifying wind-loaded slopes and traveling safely in more exposed terrain may be more difficult today. Clues like cornices above a slope, blowing snow, and wind created surface textures can help, but if you can't tell for sure, assume unstable wind slabs could exist on the slope. Slopes sheltered from the wind could hold consistent soft snow with fewer chances of instability.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Cooling temperatures during the storm combined with moderate new snow accumulations should make loose dry sluffs on steep slopes more likely than storm slabs today. They should remain relatively small and only occur in the new snow. While storm slab activity should be unlikely in most areas, storm slabs are not impossible on some isolated terrain features in areas that received the most new snow.  

Avalanche Discussion

* New wind slabs had formed in the Mt. Rose backcountry by noon yesterday and old wind slabs had become more sensitive. Ski kicks triggered shooting cracks as the stack of new and old wind slabs failed on old weak snow (near surface facets). 

* Observers reported new wind slabs forming on Red Lake Peak by noon yesterday as well. 

* Rain transitioning to snow by mid to late morning was observed at Carson Pass above 7500 ft, on Donner Summit above 7000 ft, and in the Mt. Rose backcountry above 7500 ft. Snow levels fell during the day.

Regions covered