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
1 · Faible
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Périmé — ce bulletin a expiré 7 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

MODERATE avalanche danger continues for above treeline and near treeline terrain due to wind slabs formed yesterday from deposits of wind drifted snow. Significant uncertainty exists for near treeline terrain where a wind slab avalanche yesterday was observed to have unusual characteristics. Below treeline, LOW avalanche danger continues.

Problèmes avalancheux

  • Wind Slabs

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

    Yesterday's SW winds drifted significant amounts of snow in near treeline and above treeline terrain. Newly formed wind slabs exist on NW-N-NE-E-SE aspects. The expected avalanche size is up to D2.

    A natural wind slab avalanche with unusual characteristics was observed yesterday on Elephants Hump (Carson Pass Area). This hard slab avalanche occurred in near treeline terrain on a N aspect at 8,400'. The 1 to 1.5 foot crown propagated around a corner to be about 200' feet wide in relatively small avalanche terrain. Additional shooting cracks were observed off the edge of the crown. Additional human triggered collapses were reported yesterday in the area adjacent to the crown of the avalanche. The characteristics of this avalanche suggest that there may have been faceted (sugary) snow or surface hoar underneath the wind slab. 

    Greater than usual uncertainty warrants extra caution around wind slabs today. Hard slab conditions exist above treeline. Near treeline wind slabs may avalanche wider than anticipated. Use the clues of recently wind drifted snow to identify areas of wind slab and adjust routes accordingly. Recently wind drifted snow exists below cornices, at and below rounded wind pillows, and were indicated by wind scouring vs deposition patterns along ridgelines.

     Photos of yesterday's hard wind slab avalanche. Note how the debris in the trees of the first photo extend well around the corner and continue out of view.

Avalanche Discussion

Significant amounts of blowing and drifting snow were observed near treeline and above treeline yesterday in the Carson Pass area with one natural wind slab avalanche reported. Lesser amounts of blowing snow were reported from the Mount Rose and Donner Summit areas. Recent observations from around the forecast area have noted near surface facets and surface hoar in wind protected areas below treeline. The larger open areas have held the most well developed near surface facets and the largest surface hoar. Snowpit tests targeting the buried Dec 12 rain crust have yet to show problematic weak layer formation around this crust.

Régions couvertes