Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 10 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Human-triggered wind slab avalanches will be possible today on wind-loaded slopes. Near and above treeline terrain will hold more widespread and larger wind slabs, but some wind slabs may still linger in below treeline terrain. MODERATE avalanche danger exists at all elevations. Due to unusual wind directions, wind slabs may exist in unusual places. Evaluate the snowpack and terrain carefully to identify where avalanche problems may exist and plan travel routes to avoid them.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    Continued wind and additional snowfall today will lead to another round of wind slab formation on wind-loaded slopes. The forecasted SE winds are uncommon for this area, so wind slabs will likely exist in unusual places today with direct wind-loading occurring on W-NW-N aspects and cross-loading on SW and NE aspects. Some of the wind slabs that formed yesterday will still linger on previously wind-loaded NW-N-NE-E-SE aspects, and the new wind slabs could form on top of these in some places. Human-triggered wind slabs will be possible today on all aspects in near and above treeline terrain due to the shifting winds and unusual wind directions. Some of these wind slabs may be firm and stubborn, and some could break above the person who triggers them. Some smaller wind slabs may still remain in below treeline terrain as well due to the strength of the wind over the last 24 hours. 

    Identify where wind slabs may exist using clues like blowing snow, cornices, wind pillows, ripples across a slope, firm but hollow sounding snow, and other wind created textures. Use this information to plan a route that avoids the wind slabs and utilizes more sheltered terrain where better snow for recreation will exist.

Avalanche Discussion

Yesterday observations on Andesite Ridge and Ophir Peak revealed significant wind-loading despite the limited snow accumulation. Wind slabs on Ophir Peak measured up to 8 inches in depth, and on Andesite, they grew to 14 inches in the most heavily wind-loaded areas. On Ophir Peak ski cuts and kicks on wind-loaded test slopes did not produce signs of instability, and data and observations indicated good bonding between the old and new snow. Across the Lake on Andesite Peak, refrigerator-sized cornice pieces dropped onto a test slope caused a wind slab failure that propagated a few feet wider than the cornice pieces. Ski cuts could trigger cracking on wind-loaded test slopes on Andesite Peak if those slopes were undercut first. In both areas, gale force southwest winds continued wind-loading slopes all day. 

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