Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Sun
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Heavy wet new snow and drifting snow are expected to overload weak layers within the backcountry snowpack today. A natural avalanche cycle is expected to occur in the backcountry starting sometime today and lasting into tomorrow morning.  Backcountry travelers could trigger avalanches 2 to 6+ feet deep this morning as instability rises with even larger avalanches expected once the natural avalanche cycle begins. For this reason, travel in or below avalanche terrain is not recommended today.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Gale force SW winds will drift and deposit new snow into cohesive wind slabs along the downwind side of ridgetop areas and cross-load new slabs into gully features. This will occur mainly above treeline and near treeline. Wind slabs may form below treeline to a lesser extent due to the strength of the winds.

    Travel in or below avalanche terrain is not recommended today.

    (1/12/2024) Blowing and drifting snow was observed yesterday (and the day before) due to SW winds. Photo: Public

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    2–3

    Large to very large avalanches are expected over the next 24 hours. As wet heavy snow loads the snowpack, failures could occur on a variety of weak layers at various heights within the existing snowpack. The Jan 2 persistent weak layer (PWL) (buried surface hoar, faceted snow, and/or a crust/facet combo) has been the main player in recent avalanches in the backcountry. As this storm progresses, the likelihood will increase for failure of weak faceted snow located much deeper in the snowpack around the Dec 19 rain crust or the depth hoar near ground level. Failure of either of these deeper weak layers could easily result in a size D3 avalanche.

    Recent avalanches, snow surface cracking, snowpack collapse, or whumpfing sounds will indicate unstable persistent slabs in the immediate area.  These avalanches could be remotely triggered from low angle terrain above, below, or off to the side of a steeper slope.  Travel in or below avalanche terrain is not recommended today.

    (1/11/2024) One of several avalanches remotely triggered by backcountry travelers on Jan 11. This one was remotely triggered by a snowmobile traveling in adjacent low angle terrain north of White Rock Lake near Independence Lake, CA. The depth of this avalanche was due to wind-loaded snow on top of the Jan 2 PWL. Future avalanches could fail at least this deep or deeper as the current storm progresses and the likelihood of failure on weak layers below the Jan 2 layer increases. Photo: Public

Régions couvertes