Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Tue
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

The sheer size of the avalanche that could be triggered by a backcountry traveler today is unnerving. The month of December thus far has been plagued by deep instability. This problem is still lingering and the consequences have gotten even bigger.

Problèmes avalancheux

  • Wind Slabs

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

    SW winds blowing and drifting snow during this last storm built wind slabs near treeline and above treeline in leeward areas mainly on NW-N-NE-E-SE aspects. Identify slopes of concern as areas near cornice features, slopes with large wind drifts along the top or the side, and/or wind created texture on the snow surface. Move around these areas with caution. 

    Triggering a wind slab avalanche could create a step down to a much larger deep persistent slab avalanche in some areas.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2.5–4

    This last storm just put a huge load on top of the existing snowpack. While we made it through 5 consecutive days pre storm without any additional persistent slab avalanches, the Dec 1 faceted persistent weak layer at the bottom of the snowpack continued to show signs of instability leading into this storm. The areas of greatest weakness were across NW-N-NE aspects near and above 8,000'. Any deep persistent slab avalanches that occur today will most certainly be big, and potentially historic.

    We received a report yesterday from a N aspect, 24 degree angle slope, near 7,700' elevation stating that "Partner fell out of skis, ended up wallowing shoulder deep in snow. Broke through PWL and triggered a whumpf across the whole slope. Visible cracks above on slope....No other signs of instability."

    This is often how it goes with deep slabs - no signs of instability right up until the time that the slope fails big.

    Avoidance, avoidance, avoidance is the strategy for not getting caught in an avalanche of this magnitude.  Options for reducing the risk: 1) Staying committed to sub 30 degree slopes without steeper connected terrain above or to the side. 2) Travel on SE-S-SW aspects where the Dec 1 persistent weak layer is much less likely to exist.

    (12/12/2022)

    Very large avalanche crown in Hourglass Bowl, Tamarack Peak, NV.

    Photo: Public

Avalanche Discussion

  • With improving visibility, there should be an opportunity to see if any deep persistent slab avalanches occurred naturally during the recent storm. If you see a large crown, please submit an observation with a photo and location info.
  • Any areas of buried surface hoar that existed prior to the recent storm are expected to have either already failed during the storm or been crushed by the new snow load.

Régions couvertes