Boletín de aludes

Central Sierra Nevada

Sierra Avalanche Center
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Peligro de aludes

Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 13 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

On slopes steeper than 30 degrees, MODERATE avalanche danger exists at all elevations on NW-N-NE aspects an on the near and above treeline E-SE aspects due to a combination of widespread persistent slabs and lingering wind slabs. Human triggered persistent slabs remain possible in near and below treeline terrain. Remotely triggered avalanches can occur under these conditions. 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.

I will update the advisory next on Thurday morning at 7am. 

Problemas de aludes

  • Deep Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2

    Human triggered avalanches remain possible in near and below treeline terrain on NW-N-NE aspects where the recent snow rests on top of the Dec. 7th facet layer. Any areas that had snow cover prior to this storm remain suspect. The recent snow currently represents a soft slab. Depending on how fast it consolidates or how fast it weakens the new snow may become more (faster consolidation) or less (faster weakening) slab-like. A more slab-like layer would make these persistent slabs easier to trigger.

    Since fractures can travel so easily 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 30 degrees remains possible below treeline.

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1

    Some fragile wind slabs that formed during the storm may still linger in isolated areas on the near and above treeline NW-N-NE-E-SE aspects. Most of these wind slabs should have become more difficult to trigger, smaller, and more shallow over the last few days. However, some of these wind slabs could sit on top of the persistent weak layers mentioned above on the near treeline NW-N-NE aspects. Other larger and more fragile wind slabs may also linger in more in complex or extreme terrain (unsupported slopes, couloirs , cliffy areas, etc). Human triggered avalanche activity resulting from the failure of these wind slabs remains possible.

Avalanche Discussion

More whumpfing and cracking occurred on Rubicon Peak (more info, snowpit) yesterday in N-NE facing near and below treeline terrain. As in other areas 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. The collapses in this area were less widespread, smaller, and did not travel as far as the failures that occurred in other areas over the last 2 days. Observations and snowpit data showed that while the Dec. 7th facets remain weak they have started to adjust VERY SLOWLY to the recent snow above them. Data also indicates that the recent snow layer still represents a soft slab. This recent snow has also started to weaken due to the cold clear weather across the region.

In the more wind exposed terrain near the top of Rubicon, some small wind slabs remained on the N-NE aspects. Stepping onto small wind loaded test slopes in this area did cause some small shooting cracks 3-5 ft in length. Very little evidence of east wind scouring existed in this area.

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.

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