Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

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

Points saillants

Unstable, dangerous avalanche conditions remain ongoing with conditions ripe for large and destructive avalanches.  There is a big load of recent storm snow on top of very weak snow at the base of the snowpack.  Travel with great caution in the vicinity of avalanche terrain, remembering that recent avalanches have been triggered from substantial distances away, often from the side or from below the steeper terrain.

Problèmes avalancheux

  • Persistent Slabs

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

    We are in the midst of a persistent slab avalanche cycle with the end not yet in sight.  Evidence of instability is encountered daily throughout the forecast area and avalanche events are a near daily occurrence. The persistent weak layer of sugary snow that formed during our dry spell through the 2nd half of November is now buried under 1.5 to 4 feet of snow.  Whumpfing noises, collapsing of the snowpack, shooting cracks, and large avalanches have been frequent occurrences since last Thursday as this weak snow fails under load. This persistent weak layer is most widespread on NW-N-NE-E aspects. It has been observed on all aspects in isolated areas.  Known avalanches that have occurred on this weak layer have been on NW-N-NE aspects with wide propagation, wrapped around terrain features, and have been remotely triggered from several hundred feet away.

    Large and destructive avalanches are expected again today.  Clear signs of unstable snow in your immediate area include recent avalanche activity, shooting cracks, collapsing of the snowpack, whumpfing noises, and/or unstable snowpit test results.  Two things you can do to significantly decrease your likelihood of becoming caught in an avalanche today: 1) Limit your travel only to slopes less than 30° in steepness without connected steeper terrain above or to the side. 2) Move through terrain anticipating that any avalanches triggered will be wider than expected and run longer downslope than expected.

Avalanche Discussion

  • Rain on Dec 3 did not percolate down to the faceted Dec 1 PWL in the vast majority of areas. Moisture has increased in the faceted PWL in some locations below 7,500' to 8,000'.  Snowpit tests and other signs of instability in these locations continue to indicate that the layer remains weak and unstable.
  • The faceted weak layer remains dry in most locations above 8,000'.
  • Avalanches and signs of instability continue to be reported throughout the forecast region.  Check out the observations page for more details.

Régions couvertes