Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 8 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

CONSIDERABLE avalanche danger exists at all elevations due to widespread wind slabs and some storm slabs. Large human-triggered avalanches could occur today. More avalanche fatalities occur at the CONSIDERABLE danger rating than at higher danger ratings.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2

    Gale force winds and several feet of new snow during this storm have left large wind slabs on leeward slopes. Some additional snow and moderate winds in the forecast today may add to these existing wind slabs. While the decrease in storm intensity should have decreased the chances for widespread natural avalanche activity, human-triggered wind slab avalanches remain likely today and some natural wind slabs may still be possible. Wind slab avalanches could be large and destructive. The largest and most fragile wind slabs should exist on wind-loaded NW-N-NE-E-SE aspects in near and above treeline terrain, but some may also exist in wind-exposed areas in below treeline terrain due to the pervasive SW winds. 

    Cornices above a slope, blowing snow, wind drifts/pillows, and other wind created textures can help identify where wind slabs may exist. Using this information to plan a cautious route around potential wind slabs with conservative buffer zones represents a prudent choice for today. Less wind-exposed and/or lower angle terrain should hold softer less variable snow.

  • Loose Dry

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2

    Changing conditions during the storm have deposited a variety of storm snow layers. Some of these could serve as weak layers and some could represent slab layers. Human triggered storm slab avalanches will remain possible today on steep slopes in sheltered terrain. The likelihood of natural storm slab activity should have decreased as the storm intensity waned and as temperatures have steadily declined. Some loose dry sluffs could also occur in the new snow on steep slopes today. Storm slab avalanches could be large today especially if they break on one of the deeper weaknesses within the storm snow.  

    Before committing to any slopes, look for clues about potential storm slab instability like recent avalanche activity, cracking and collapsing, and/or results on test slopes. Use this information to identify areas where storm slabs may exist and build appropriate safety margins around this problem. Sticking to lower angle terrain without overhead hazard could be one way to have fun with a nice safety margin. 

Avalanche Discussion

* Observations from Donner Ridge and Incline Lake Peak yesterday found blizzard conditions with intense blowing snow and gale force winds. Widespread skier-triggered shooting cracks occurred in wind-affected areas in both places. On Incline Lake Peak, cornices above test slopes failed easily. On Donner Ridge wind slabs extended into some treed areas.

* In more sheltered areas on Incline Lake Peak and Donner Ridge, deep storm snow existed with several different layers including light snow below heavy snow and some other storm snow weaknesses. One ECTP result was reported from Incline Lake Peak on a density change. 

* Other observations during this storm have also found reactive wind slabs as well as weaknesses in the storm snow. 

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