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

Moderate avalanche danger exists for all elevations and aspects on slopes 35 degrees and steeper due to wind slab and loose wet avalanche problems. Locations in the northern portion of the forecast area will be most prone to these avalanche problems today. Locations in the southern portion of the forecast area where little to no new snow accumulated over the past 36 hours will have more limited loose wet avalanche problems today and no wind slab avalanche problems.

Problèmes avalancheux

  • Wind Slabs

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

    In the northern portion of the forecast area, strong to gale force NE winds will redistribute the recent new snow on the ground and create fresh wind slabs in near treeline and above treeline areas on SE-S-SW-W-NW aspects today. These wind slabs are generally expected to be small in size, but could bury a person in a terrain trap. Some of these wind slabs could take on wet slab characteristics today.

    Look for, identify, and avoid areas of potentially unstable wind slab. Use clues such as recent avalanche activity, blowing snow, new cornice and wind pillow formation, and human triggered snow surface cracking to determine where wind slabs exist.

  • Loose Wet

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

    Loose wet avalanche problems are expected to form today in sun exposed areas on all aspects at all elevations. In locations with a couple inches or more of recent storm snow, loose wet avalanche problems are expected to form quickly this morning. Hard melt-freeze crust below the recent storm snow will act as an efficient bed surface for avalanche activity today allowing for the potential of long running avalanches. In areas where little to no recent storm snow exists and the snow surface is composed of hard melt-freeze crust, loose wet avalanche problems will form more slowly today, likely holding off until the afternoon hours.

    In areas with recent storm snow, natural and human triggered roller balls and pinwheels will be the clues of developing wet snow instability. In areas without recent storm snow, loss of on foot supportability of the surface melt-freeze crust will indicate when the amount of surface wet snow is becoming problematic.

Avalanche Discussion

Observations made yesterday on Andesite Ridge (Donner Summit area) revealed signs of instability were limited to loose dry avalanches. New snow amounts of 4 inches were present. Wind loading was isolated at 12 to 18 inches deep but did not extent more than 3 feet down slope. Bonding of new snow to the old snow melt-freeze crust surface was fairly poor, but some cohesion was observed. New snow was cohesive and moist but still acting like loose dry avalanches on test slopes in response to ski cuts. Sun breaks on the Sierra Crest yesterday morning were very infrequent and always lasted less than 3 minutes in the Donner Summit area. Despite the isolated periods of sun, a thin sun crust formed quickly in open areas on E-SE aspects.

Régions couvertes