Bulletin d’avalanche

Central Sierra Nevada

Sierra Avalanche Center
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Danger d’avalanche

Fri
Alpin
5 · Très fort
Limite forestière
5 · Très fort
Sous la limite
5 · Très 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

Gale force winds and intense snowfall continue to overload the snowpack. This extreme load combined with new and old weak layers in the snowpack have created very dangerous and complicated avalanche conditions. Large, deep, and destructive avalanches are almost certain today.  The avalanche danger is EXTREME.  Fortunately, the travel advice is simple: avoid traveling on any steep slopes, under any steep slopes, near any steep slopes, or across any runout zones. Avoid travel in, near, or below avalanche terrain.

Problèmes avalancheux

  • Persistent Slabs

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

    Buried surface hoar, near crust facets, and older facet layers all existed in the snowpack before the storm dropped several feet of new snow in a short amount of time. These pre-existing weak layers are likely to break under this rapid addition of such a large load resulting in large persistent slab avalanches. These kinds of avalanches often propagate farther and wider across slopes and can be triggered remotely. Some of them may even break down on the Dec 11 facet layer and involve almost the entire snowpack, especially where a shallow and weak snowpack previously existed like in the Carson and Ebbetts Pass areas. 

    These avalanches could run long distances and be very large and deep.  Avoid travel in, near, or below avalanche terrain.

  • Wind Slabs

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

    Gale force winds shifting between the S and SW combined with several feet of new snow have created deep slabs of drifted snow on leeward aspects. Wind slabs may exist in some unusual places due to the southerly winds. Many wind-loaded slopes likely avalanched during the night, have since refilled, and are ready to slide again. Large wind slab avalanches will continue to occur today on steep wind-loaded slopes especially in near and above treeline terrain. Large fragile cornices also exist above many slopes. Any wind-loaded terrain or terrain below cornices is suspect.

    Wind slab avalanches could break more than 6 ft deep and run long distances into below treeline areas and lower angle terrain. Avoid travel in, near, or below avalanche terrain.

  • Storm Slabs

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

    Changing conditions during the storm including warming temperatures, fluctuating snowfall rates, and shifting winds have created weaknesses within the storm snow. Avalanches involving slabs of new snow that failed on these weaknesses likely occurred during the night. Similar storm slab avalanches remain likely today on any steep slope on any aspect.

    Storm slab avalanches could involve part or all of the storm snow.  Avoid travel in, near, or below avalanche terrain.

     

Avalanche Discussion

* A large wind slab avalanche was reported on Silver Peak yesterday that likely failed on buried surface hoar.

* Several small test slopes failed on buried surface hoar near Brockway Summit. More test slope failures were reported from near Bear Meadows (Litte Truckee Summit).

* Snowpit data from Powderhouse Peak, Jakes Peak, Silver Peak, and Brockway Summit all identified various weak layers in the snowpack including buried surface hoar, near crust facets, and the Dec 11 PWL. 

* With numerous weak layers in our current snowpack from the now buried surface hoar layers, near crust facets, and the lingering Dec 11 PWL, the existing snowpack is in poor condition to handle the major new snow load.

Régions couvertes