Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

HIGH avalanche danger exists at all elevations in the backcountry at this time. Conditions are dangerous and travel in or below avalanche terrain is not recommended. This includes steep slopes below treeline.

Problèmes avalancheux

  • Wind Slabs

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

    Large amounts of wind drifted snow in above treeline and near treeline areas has created a wind slab avalanche problem. This exists mainly in lee areas on NW-N-NE-E-SE-S aspects with previous snow cover. Avalanche size is expected at D2 to D3. Avoid travel in or below avalanche terrain. Avalanches may run significant distances into flat areas below steep slopes. Keep in mind that poor visibility may make it difficult to see steep slopes above you.

  • Loose Dry

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1

    Weak layers existing within the new snow were becoming apparent yesterday afternoon with additional weak layers expected to form in the new snow last night and today. This will allow for a storm slab avalanche problem to exist in wind protected areas near treeline and below treeline on all aspects with previous snow cover. Loose dry avalanches could also occur in these same areas. Avalanche size is expected at D1 to D2. Travel on steep slopes below treeline is not recommended today.

  • Storm Slabs

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

    Feet of new snow has been loaded on top of weak faceted (sugary) snow a few inches below the old/new snow interface near treeline and below treeline on NW-N-NE aspects. This has introduced the possibility of a Deep Slab avalanche problem with an expected avalanche size of D2 to D3. Any deep slab avalanches will involve all of the accumulated new snow, plus the additional depth of wind drifted snow if occurring near treeline. Large avalanches may occur in below treeline areas on slopes with a history very infrequent avalanches. Travel on steep slopes below treeline is not recommended today. Becoming caught in a deep slab avalanche near or below treeline may not be survivable.

Avalanche Discussion

* Drastic differences in new snow accumulation between the Sierra Crest and the eastern side of the forecast area were observed most of yesterday. New snow accumulation began to increase significantly on the eastern side of the forecast area late yesterday afternoon and overnight.

* On NW-N-NE aspects near treeline and below treeline a layer of weak faceted (sugary) snow exists a few inches below the old/new snow interface. On other aspects, new snow is deposited on top of a thick melt-freeze crust.

If you insist on going into the backcountry today, make a well defined plan that avoids all potential avalanche terrain and all low angle runout zones below adjacent avalanche terrain. Make sure all group members understand and agree to the plan. Call out anyone in your group who deviates from this agreed upon plan. Anticipate and plan for navigation in very poor visibility with disappearing tracks. Plan for challenges to communication between group members from high winds, blowing snow, wet, low visibility weather conditions. Plan for very delayed or impossible rescue due to dangerous conditions if someone gets hurt.

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