Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Alpin
1 · Faible
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 13 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

MODERATE avalanche danger continues near treeline and below treeline on NW-N-NE aspects on slopes 32 degrees and steeper due to ongoing instability of persistent slabs.

Human triggered avalanches remain possible. Pay attention to the big picture of surrounding terrain and the presence of steeper slopes above. Understand that remote triggering of avalanches from low angle slopes below to steeper slopes above is very possible under the current snowpack conditions.

Problèmes avalancheux

  • Deep Persistent Slabs

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

    It has now been a week since the last significant snowfall and it remains game on for avalanches. The areas with the deepest snowpack continue to hold the greatest amount of avalanche danger. Near treeline and below treeline slopes on NW-N-NE aspects that resisted scouring by the Nov 21-23 ENE gale force wind event hold significant amounts of faceted snow. This is the persistent weak layer below the overlying slab of recent storm snow from Dec 6-7.

    Beware of steeper terrain above as remote triggering of avalanches from low angle terrain below is very possible under the current snowpack conditions.

Avalanche Discussion

Persistent weak layers are the name of the game right now with little improvement in snowpack stability observed over the past week. Recent observations from around the forecast area continue to show the presence of the weak Dec 7 facet layer (sugary snow) in the bottom half of the snowpack on the vast majority of near treeline and below treeline NW-N-NE aspects. Where this was once several layers of crusts and facets, it is continuing to metamorphose into an increasingly homogenous facet layer as the crusts facet and erode. Human triggered snowpack collapse with whumphing sounds remains widespread in these areas along with unstable snowpit test results. Once collapse of the weak layer is triggered, propagation over distances of a few tens of feet to a few hundred feet have been observed.

Barely covered rocks, stumps, and/or logs that exist on most slopes present an additional hazard to backcountry travelers. There are very few areas where the shallow snowpack has enough structure or strength to keep a person from hitting these objects. The snow cover mostly serves to camouflage their presence.

Régions couvertes