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 13 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

CONSIDERABLE avalanche danger exists on slopes 32 degrees and steeper on all aspects above 7000 ft. due to wind slabs, storm slabs, and deep persistent slabs resting on a variety of weak layers. Below 7000 ft. where more of the storm's precipitation fell as rain, less avalanche danger exists. Even though the best window for natural avalanches has passed, human triggered avalanches remain likely today. Large, deep, and destructive avalanches could still occur today.

Problèmes avalancheux

  • Wind Slabs

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

    Large wind slabs exist above a variety of weak layers on the wind loaded NW-N-NE-E-SE aspects in near and above treeline terrain. Observations have shown these wind slabs at 3-6+ ft in depth. The weak layers under the slabs have not had time to adjust to this large heavy load and human triggered avalanches will remain likely where these wind slabs exist. Large destructive avalanches would result from the failure of these wind slabs.

  • Loose Dry

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

    This storm started out cold and and grew progressively warmer until last night. This warming trend created an upside down snowpack with lighter softer snow resting below heavier more dense snow layers. Below all of that storm a variety of weak layers ranging from facets above a rain crust to even softer colder snow from earlier storms exists. This combination of heavy snow sitting above weak snow layers means that human triggered avalanches remain likely even in non-wind affected areas. These storm slabs avalanches could also be large and destructive. 

  • Storm Slabs

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

    In areas above 9,500' deep persistent slabs linger near treeline and below treeline on NW-N-NE aspects. Weak layers of well developed facets and depth hoar remain buried in the snowpack in these areas. With the load above these old weak layers more than quadrupling since last week, human triggered deep slab avalanches remain possible today. Locations that are both above 9,500' and near treeline or below treeline terrain represent only a small portion of the forecast area, keeping this problem isolated in distribution.

Avalanche Discussion

Yesterday on Tamarack Peak and on Andesite Ridge, the remains of several natural avalanches existed on N-NE aspects. The crown depths on these avalanches measured 2 to 4 ft and the slides all entrained enough snow to deeply bury people. The failure layer for these avalanches appeared to be a layer of light soft snow. Some of avalanches stepped down to lower older weak layers and the ground. Tests and snowpit data in both of these areas yesterday showed that the weaknesses still remained active. Skier triggered whumphing, collapsing, and shooting cracks occurred on all aspects in the Tamarack Peak area yesterday. A piece of cornice dropped onto a wind loaded test slope also triggered a small wind slab failure on that test slope in the Tamarack Peak area yesterday.

On Andesite Ridge, rising snow levels allowed rain to fall on snow up to 8200 ft. Ski cuts on wet test slopes did release some small wet loose snow instabilities like pinwheels and roller balls.

Régions couvertes