Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 7 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

A low likelihood high consequence persistent slab avalanche problem lingers below treeline and near treeline with ongoing isolated instability. Lingering wet snow surface conditions below 8,500' may allow for some very small loose wet avalanches. Wind and light snow last night may have created isolated slabs of wind drifted snow near and above treeline. MODERATE avalanche danger exists at all elevations.

Problèmes avalancheux

  • Deep Persistent Slabs

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

    Lingering, isolated instability exists below treeline and near treeline on NW-N-NE-E aspects. The sugary Jan 4 crust/facet persistent weak layer in these areas is gaining strength but not at the same rate in all locations. Spatial variability of stable vs unstable is increasing. In most below treeline locations, this weak layer is buried 1 to 2 feet below the snow surface. In some near treeline areas, this weak layer is buried up to 8 feet below the surface under wind drifted snow. Human triggered avalanches size D2 to D3 have become unlikely on a regional scale, but an isolated avalanche is still a concern.

    A low likelihood high consequence avalanche problem is what remains at this time. We are close to but not quite past this avalanche problem on a regional scale due to the continued signs of isolated instability. Make conservative terrain and route selections in any areas where unstable snowpit test results or other signs of instability exist.

  • Loose Wet

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

    Wet snow surface conditions will remain in some areas today below 8,500'. Some rollerballs or very small loose wet avalanches are possible today. Avalanche size is expected at D1. Problematic consequences of being caught would come from downslope terrain hazards such as cliffs and terrain traps below.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1

    In isolated areas above treeline and near treeline, small unstable slabs of wind drifted snow may have formed last night. Slopes below cornice features are the most suspect. Avalanche size is expected at D1 with up to D2 possible in the most heavily wind drifted areas where over two inches of new snow fell last night. Move cautiously around cornice areas in locations where 2+ inches of new snow are present.

Avalanche Discussion

* Wetted snow surfaces were reported yesterday from the Echo Summit and West Shore Tahoe areas with some rollerballs and pin wheels occurring.

* Surface hoar 2-9 mm in size was reported yesterday on northerly aspects in the Echo Summit and Luther Pass areas.

* Snowpit tests targeting the persistent Jan 4 crust/facet layer have shown increasingly variable results over the past several days with isolated areas of unstable test results continuing. Clearly unstable snowpit test results were observed yesterday on Stoney Ridge (West Shore Tahoe area) while at the same time several snowpits in similar terrain on Waterhouse Peak (Luther Pass area) gave no indications of ongoing instability. Five days have past since an avalanche was reported to have failed on the Jan 4 weak layer.

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