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
2 · Modéré
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Périmé — ce bulletin a expiré 12 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Human-triggered avalanches are likely (CONSIDERABLE danger) on NW-N-NE aspects steeper than 32 degrees due to wind slabs (all elevations) and deep persistent slabs (above 9000 ft). In other wind loaded areas on NW-N-NE-E-SE aspects human triggered avalanches will be possible (MODERATE danger) on slopes 35 degrees and steeper. Strong winds may mean wind slabs formed at lower elevations and in atypical areas. In areas east of Lake Tahoe where less snow fell, less avalanche danger will exist. 

Problèmes avalancheux

  • Wind Slabs

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

    New snow and wind during this storm have formed wind slabs on wind-loaded NW-N-NE-E-SE aspects. Due to the strength of the winds associated with this storm wind slabs likely exist in some areas that typically remain sheltered from the winds. The largest wind slabs will exist in near and above treeline terrain, but some may have formed in below treeline terrain as well. Additional snow and wind today will increase the size and extent of these wind slabs. Human triggered wind slab avalanches are possible today anywhere wind slabs exist and are likely on the most heavily wind loaded slopes along the Sierra Crest especially if these wind slabs have formed above the persistent slabs mentioned below. Wind slab avalanches deeper than 3 ft are possible today in heavily wind loaded areas along the Sierra Crest and could break to the ground if they trigger the persistent slabs below them.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    3

    Even thought snowfall amounts ended up less than forecasted, the additional weight will push the persistent weak layers near the base of the snowpack on some NW-N-NE aspects above 9000-9500 ft. close to their limit. Triggering a deep persistent slab avalanche will be possible today where these layers exist and are continuous. In areas where wind slabs sit on top of the persistent slabs, human triggered deep persistent slab avalanches are likely. These avalanches would break near the ground, involve the entire snowpack, can release on less steep slopes, can be triggered from a distance, and have very serious consequences. For these reasons any terrain that has the potential for deep persistent slabs is suspect and deserves extra caution or better yet avoidance, even though some uncertainty still remains concerning how continuous and widespread these layers are.

Avalanche Discussion

Yesterday above Red lake on Carson Pass small wind slabs had already started to form with only about an inch of new snow accumulation. These wind slabs formed on top of a mix of thin crusts and some softer snow in the areas below 8500 ft. Recent data from other places around the forecast area continue to reveal the presense of weak sugary snow layers near the base of the snowpack on northerly aspects above 9000 to 9500ft. Tests on these persistent weak layers keep indicating that if these layers break the resulting fracture could travel through the persistent weak layers.

Snow covered mountains, improving weather, and fresh tracks will make it easy to forget about today's avalanche problems. For some advice on dealing with various avalanche problems check out this page.

Régions couvertes