Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
1 · Debole
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 13 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

On slopes steeper than 32 degrees, MODERATE avalanche danger exists on near and below treeline NW-N-NE aspects due to lingering persistent slabs. Human triggered persistent slabs remain possible. Remotely triggered avalanches can occur under these conditions. Some isolated areas of unstable snow may still remain on above treeline slopes as well.

In addition to the avalanche danger a myriad of season-ending obstacles still lurks just below the surface. Conservative terrain selection, careful snowpack evaluation, and conservative decision-making are essential.

Problemi valanghivi

  • Deep Persistent Slabs

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

    Human triggered avalanches remain possible in near and below treeline terrain on NW-N-NE aspects where weak sugary snow exists under the snow that fell on Dec. 7th. While the vast majority of these persistent slabs exist in near and below treeline terrain, the possibility remains that some isolated areas above treeline where snow did not get scoured away earlier this season could pose a problem. The recent snow has enough cohesion to act as a soft slab sitting above the Dec 7th facets. Even though some data indicates that the snowpack has become less fragile, the additional weight of a person on a slope where this persistent weak layer/soft slab combination exists can still cause the slope to fracture. Unstable conditions like these take a long time to change and often catch people off-guard.

    Since fractures can travel through the persistent weak layer, people can trigger persistent slabs remotely while standing in low angle terrain or on ridgelines or anywhere that the snowpack under their feet connects to steeper and/or deeper terrain. Wide propagation and avalanche activity on lower angle slopes to around 32 degrees remains possible below treeline.

Avalanche Discussion

Another day of widespread collapsing and whumpfing yesterday near Red Lake on Carson Pass (more info, snowpit, video). These collapses happened when the weak sugary snow (Dec. 7th facets) below the recent new snow broke and a fracture propagated along the weak layer. Several of these whumpfs and and collapses happened near areas that had previously collapsed. Snowpit tests also indicated that when the facet layer breaks, the resulting fracture can travel along this persistent weak layer. Data also indicates that the snow layer above the Dec. 7th facets continues to represents a soft slab.

Barely covered rocks, stumps, logs, and other hard, immobile, season-ending, equipment-breaking objects still exist on all slopes. The shallow snowpack does not have enough structure or strength to keep a person above all these things. It only camouflages their existence.

Regioni coperte