Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 8 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Expect the avalanche danger to rise quickly as the storm impacts the area. Unstable slabs of new snow will form first in wind-loaded areas and spread to sheltered terrain below treeline as storm snow intensifies. Monitor the rapidly changing conditions. Stepping back from steep slopes and recreating on lower-angle, non-avalanche terrain can help reduce the risk of getting caught in an avalanche today.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Pay attention to the quickly changing conditions today. Slopes that were dirt may become snow-covered and avalanche-prone, and new snow may create unstable slabs on slopes that were ok a few hours ago. Clues such as recent avalanches, test slope failures, snow surface cracking, and unstable test results can indicate the presence of unstable storm slabs. You can still enjoy the new snow and reduce your exposure to avalanche problems by recreating on lower-angle, non-avalanche terrain without overhead hazards like other steep slopes or looming cornices.

    A series of winter storms that get progressively colder will bring heavy snow and wind to the region through Friday. Significant new snow should accumulate at all elevations, even though some of the initial precip may include rain below 7500 ft this morning. The snow will likely accumulate faster than it can bond to itself and the snow below it. Weaknesses may also form in the storm snow, like lighter layers of storm snow or graupel. 

    Unstable snow will form first in areas where blowing snow fills in the downwind side of ridges, gullies, and open slopes with fresh slabs of wind-drifted storm snow. As more snow piles up today, unstable slabs of storm snow will spread into more sheltered areas. Enough snow should fall for avalanches large enough to bury or injure people to become likely on steep slopes in both wind-loaded and wind-protected areas across all aspects by this afternoon. Locally deeper, stiffer slabs of storm snow will form in wind-loaded areas and could result in larger avalanches. In sheltered areas, storm slabs may be less deep and softer but still dangerous. 

Avalanche Discussion

Collision hazards with rocks, bushes, stumps, down trees, and open water continue to exist.

We had an early start to our winter with snow and rain in October through mid-November.  After a 3+ week dry spell in late November into December, the upper snowpack became weak, faceted, sugary snow.  Widespread snow loss occurred with warm temperatures and high elevation rain that followed, leaving a 1-2' snowpack above 8500-9000' on mostly northerly aspects. The recent storm rained up to ~10,000 ft and soaked those old weak layers, changing them into wet snow. This change and the compression added by the strong new snow above the old weak layers have allowed them to gain strength.  Most data now indicate that these old, weak layers have gained sufficient strength to support the snow above them. 

Regioni coperte