Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Thu
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dangerous avalanche conditions exist today with recent rain and heavy snow on top of an existing weak snowpack.  Additional rain and high elevation snow is expected to continue for today.  Conservative terrain choices are key to avoid todays complex avalanche problem.

Problèmes avalancheux

  • Persistent Slabs

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

    Recent rain and high elevation snow has overloaded our weak snowpack structure.  Multiple reports yesterday showed shooting cracks, collapsing, and whumpfing sounds on these weak layers.  Additional rain and snow overnight and through today will add more weight to these large slabs that have formed above our weak snowpack.  Large avalanches are expected to occur today.  These avalanches could fail at or near the ground taking all or most of the snowpack downhill.  These avalanches could be large and destructive with a high chance of trauma with any avalanche involvement.  The recent high snow levels and limited available terrain will push backcountry users into areas where the weakest snow exists on northerly aspects above 8000’.  

    Recent avalanches, snow surface cracking, snowpack collapse, or whumpfing sounds can indicate unstable, persistent slabs.  Persistent slab avalanches can break wider than expected, and can be triggered from a distance or low on a slope. The consequences, variability, and unusual nature of this avalanche problem make conservative terrain choices and wide safety margins prudent. If you see any signs of unstable snow or have doubts about a slope, assume it is unstable. 

    (12/19/2023)

    Large shooting cracks near Tamarack Peak, Mt Rose area.

    Photo: Public

Avalanche Discussion

A weak faceted (sugary) snowpack exists on most NW-N-NE aspects, especially in areas above 8000 ft.  Near and below about 8,500', faceted snow exists near buried rain crusts. Above 8,500', the rain crusts gradually disappear, and almost the entire lower half of the snowpack becomes weak faceted snow. The higher you go on wind-protected NW-N-NE aspects, the weaker the snowpack. These weak layers are well developed, with depth hoar found at the base of the snowpack in many areas.

There is still the potential to hit many obstacles (rocks, logs, open water, bushes, etc.) that are barely covered (or not) by the shallow snowpack. This is especially true in areas below 7,500' and very rocky areas up to at least 8,000'. Anticipate encountering a different snowpack structure and a different set of travel conditions if you are moving from one place to another around the forecast area.

Régions couvertes