Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

CONSIDERABLE avalanche danger exists at all elevations due to widespread wind slabs and storm slabs. Widespread human-triggered avalanches are likely today, and some natural avalanches may remain possible. These avalanches could be large, deep, and destructive. Dangerous avalanche conditions exist. Carefully evaluate the snowpack and terrain before committing to any slopes and plan routes to avoid avalanche problems using conservative terrain choices. CONSIDERABLE is the danger rating where the most avalanche fatalities occur.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    3

    While the best window for natural avalanches may have occurred last night, large, deep, destructive, and widespread human-triggered wind slab avalanches remain likely today. The wind slabs that formed during the storm are deep and likely have not bonded to the snow below them. Wind slabs could exist on wind-loaded W-NW-N-NE-E-SE aspects at any elevation where wind-loading occurred including below treeline terrain. The largest wind slabs could be considered deep slabs. They could have crowns deeper than 4 to 6 ft and would likely be unsurvivable. The deepest and most fragile wind slabs should exist in near and above treeline terrain.

    Blowing snow, cornices, wind drifted snow, and other wind created features and textures can help identify where wind slabs may exist. Avoid those areas and the runout zones of potential wind slab avalanches. 

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2

    Human-triggered storm slab avalanches will remain likely today. Rapid snowfall and fluctuations during the storm created slab layers and weak layers within the storm snow during the last 24 hours. A distinct density change exists at the bottom of the storm snow and could still remain sensitive to human triggering today. Like the wind slabs mentioned above, natural storm slab avalanches may remain possible today, but most of the natural storm slab avalanches should have occurred last night. The largest of these storm slabs could involve most of the new snow and be several feet in depth. Any steep slopes with new snow on them hold the potential for storm slab avalanches. 

    Clues like cracking, collapsing, and whumphing can help identify where storm slabs may exist as can digging into the snowpack with your hands or probing with a pole to look for layers in the storm snow. Use these clues to avoid steep terrain where storm slabs may exist. Storm slabs can exist on tree covered slopes in the openings between trees and may connect across some of these open spaces. 

Avalanche Discussion

Yesterday observations in Deep Creek (between Squaw and I80), near Watson Lake and in Negro Canyon (Donner Summit), and in Third Creek (Mt. Rose) all showed a dense heavy layer of snow resting on top of a lighter layer of older snow. In Deep Creek and Third Creek, some storm slab avalanche activity was noted on steep sheltered slopes and likely failed at this interface in the upside down snowpack. Skier triggered cracking occurred in sheltered areas in Deep Creek as well. Near the top of Negro Canyon and in Third Creek, ski cuts and kicks triggered shooting cracks in wind loaded terrain and some natural wind slab and ski cut triggered wind slab activity was observed. A snowmobile cut on a N-NE facing test slope near Watson Lake also triggered a small wind slab avalanche. Snowmobiles also triggered a large whumph in the Watson Lake area with noticeable collapsing on a sheltered low angle slope. Wind loaded slopes in Deep Creek held stiff wind slabs and large but fragile cornices. We also received a report of a natural avalanche on Highway 89 during the night that was large enough to bury cars.

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