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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Points saillants

A powerful storm continues to drop impressive amounts of precipitation across the forecast area.  Lowering snow levels are expected this afternoon and evening. Large and destructive avalanches that run long distances into below treeline areas could occur.  Travel in, near, or below avalanche terrain is not recommended today.

Problèmes avalancheux

  • Wind Slabs

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

    Gale force SW winds with gusts around 100 mph over exposed ridges and peaks will continue today.  Large, thick slabs of wind drifted snow will continue to form in lee areas above the rain/snow line. Wind slabs will become more widespread in near treeline and above treeline terrain as snow levels lower this afternoon. Wind slabs may also form to a lesser extent in below treeline terrain due to the intense winds.  Wind slab avalanches could become wet as they run downslope and entrain large amounts of wet snow.  Natural avalanche activity is expected today.  These avalanches could run long distances and continue down into below treeline areas. Travel in or below avalanche terrain is not recommended today.

    (12/30/2022)

    Natural wind slab avalanche, cornice fall triggered, Wildflower Ridge, NE aspect at 7,800'. Donner Summit, CA

    Photo: Steve Reynaud

  • Loose Wet

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

    Heavy rain continues to fall on the snowpack in many areas. Small to large wet loose avalanches remain a concern in all areas where rain on snow is occurring. Travel in avalanche terrain is not recommended today. After snow levels fall today, concern for this avalanche problem will diminish and a storm slab avalanche problem will take its place.

  • Storm Slabs

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

    After snow levels lower today, snowfall rates of 2 to 4 inches per hour are expected. While this will be a warm to cold snowfall event which can reduce the likelihood of instability developing within the new snow, the sheer intensity of expected snowfall cannot rule it out. New snow may accumulate faster than it can bond together. As new snow amounts approach 8 to 12 inches in wind protected areas below treeline and near treeline, anticipate the potential for a storm slab avalanche problem. As stated before, travel in or below avalanche terrain is not recommended today.

Avalanche Discussion

Poor visibility has limited avalanche data over the past 24 hours. We do know that:

  • Natural wind slab avalanches at least to size D2 occurred yesterday and the day before. Some had wide propagation. Cornice collapse has been a common trigger.
  • Some size D1 to D1.5 wet loose avalanches were reported yesterday.
  • The upper snowpack is rain soaked in many areas below about 8,500' to 9,000'.
  • Creek flows in snowcovered areas have increased, indicating rain water percolating through the snowpack in at least some areas.

Régions couvertes