Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Wed
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

Large avalanches have been observed during the past 24 hours and dangerous avalanche conditions will continue today. Heavy snowfall continues to overload a weak snowpack allowing for very wide avalanches to occur that may run down into mature forest. Travel in, near, or below avalanche terrain is not recommended today.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2–3

    Heavy snowfall and gale force winds leading to intense blowing snow have created very rapid snow accumulation rates along and just below ridgelines on NW-N-NE-E-SE aspects. Unstable snow with ongoing natural and human triggered avalanches are expected today. In areas where this heavy load of new snow has drifted in on top of weak snow from before the storm avalanches can be very wide and wrap around numerous corners. This type of avalanche behavior was observed yesterday. Unstable conditions are expected to continue today, even after wind speeds and snowfall rates decrease this afternoon.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2–3

    We saw avalanches yesterday that failed as wide as the terrain would allow, up to nearly 900' wide yesterday across the Far East Ridge of Tamarack Peak, NV in the Mount Rose zone. The issue is faceted weak old snow at the old snow/new interface (Dec 11 layer) as well as faceted weak old snow down deeper (Nov 9 layer). The Dec 11 layer was very unstable yesterday with widespread cracking, collapsing, and whumpfing. While the Nov 9 layer is limited to NW-N-NE aspects above 8,500', the Dec 11 layer is more widespread across NW-N-NE-E-SE aspects and has been observed as low as 6,800' leading to snow surface cracking over smooth ground. These weak layers are a problem both above and below treeline and in both wind protected and wind drifted areas.

    Don't mess around with this stuff right now. Avalanches could easily be larger than expected and occur in unexpected locations. These avalanches could be triggered from low angle terrain below or to the side of a slope. If traveling non-avalanche terrain today it is critical that you know your exact proximity to any avalanche terrain nearby. Even if you are in the trees you could get hit from above.

    (12/13/2021)

    R5, full path width avalanche propagation on Dec 11 facet layer at old/new snow interface. This avalanche was nearly 900' wide and wrapped around numerous corners.

    Photo: Brandon Schwartz

  • Storm Slabs

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

    To top it all off there has also been and will likely continue to be instability within the storm snow itself. Unstable storm slabs are expected in wind protected areas below treeline on all aspects. There has been enough new snow that storm slabs can be an issue even in areas that were bare ground prior to the current storm. Once again, travel in, near, or below avalanche terrain is not recommended today.

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