Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

You could trigger an avalanche today that is either a surface instability formed from blowing and drifting snow following a wind shift, or a deeper instability associated with weaker old snow at the bottom of the snowpack. Each require a different approach to terrain management. Intentional route planning and very specific terrain selection are recommended. The next update to this forecast will occur on Friday, Nov 29.

Problemi valanghivi

  • Wind Slabs

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

    On Tuesday night, a 180 degree wind shift from SW to NE occurred. This drifted and redistributed snow on the ground. The most likely place to trigger an avalanche today is in locations where a cohesive slab of locally deeper wind-drifted snow has formed. Colder than average air temperatures during wind slab formation may prolong instability. 

    Visual clues exist to identify where potentially unstable wind slabs exist. Blowing snow, cornice formations, snow drifts, and snow surface texture indicated current or past drifting snow conditions. Use these clues to identify slopes of concern near ridgetops and gully features. Move cautiously around them.

    (11/24/2024)

    Minor cracking above the skin track on a small wind-loaded slope.

    Photo: Sierra Avalanche Center

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    In specific types of terrain, weaker faceted snow lingers at the bottom of the snowpack. Over the past two days, it has become harder to trigger an avalanche on this weak layer. We need to continue to manage this avalanche problem for a few more days while we let the snowpack continue to gain strength. Keep in mind that the snowpack does not gain strength at equal speed in all locations. Any avalanches that fail near ground level will easily be large enough to bury a person, maybe even break a tree or two. Please give our current the snowpack the respect it deserves while it continues to stabilize.

    The areas with the greatest chance of a persistent slab avalanche occurring are at and below treeline across NW-N-NE aspects above 8000'-8500'.  In isolated areas, a snowpack structure conducive to this avalanche problem has also been observed above treeline or on E aspects. As this avalanche type becomes harder to trigger, don't expect to get much feedback from the snowpack in the form of collapsing or cracking as alerts to instability.

    This avalanche type can be triggered low on a slope and from low angle terrain. Move through terrain with this in mind. You can use terrain to manage/avoid this avalanche problem. The easiest way is to choose slopes less than 30 degrees in slope angle, without steeper connected terrain above or to the side. A bit more nuanced is to seek out slopes below about 8,000' where previous rain destroyed the weak layer of concern.

    (11/26/2024)

    There is a distinct difference in snow at the bottom of the snowpack where this avalanche problem exists. Pole probing has been effective at feeling for the presence or absence of a weak layer at the bottom of the snowpack. NNW aspect at 9,650' near Incline Peak, NV.

    Photo: Sierra Avalanche Center

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