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
1 · Débil
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Desactualizado: este boletín caducó 11 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Human triggered avalanches will remain possible today on slopes 35 degrees and steeper on all aspects above treeline and on NW-N-NE-E-SE aspects and in near treeline terrain. MODERATE avalanche danger exists in those areas. Shifting winds mean that wind slabs could exist in any of these areas. Evaluate snow and terrain carefully before committing to a slope.

Problemas de aludes

  • Wind Slabs

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

    Strong east winds will create new wind slabs on the SW-W-NW aspects and could cross load the S and N aspects as well. These new wind slabs should remain confined to areas along wind loaded ridges in above treeline terrain and not extend very far down slope, but they could still involve enough snow to cause problems for backountry travelers. These new wind slabs will be sensitive to human triggering today.

    The scouring east winds will remove yesterday's wind slabs from some slopes, diminish them on others, and turn them into hard slabs on still others. Also the east winds may not impact all of the slopes where previous wind slabs existed. Some of yesterday's wind slabs could remain on the near treeline NW-N-NE-E-SE aspects as well as some of the above treeline slopes that face that direction but have some protection from the strong east winds. In areas where these older wind slabs remain human triggered avalanches remain possible as well. Couliors, steep cliffy areas, and other complex or extreme terrain may be the best places to find older wind slabs that remain unstable, but they could also still exist on any previously wind loaded slope that has not been fully scoured. These slabs could take the form of hard wind slabs that sound hollow below them on some slightly scoured slopes or may remain softer on the slopes protected from the east winds. 

Avalanche Discussion

Yesterday observations on N-NE facing wind loaded test slopes along Donner Ridge between Sunrise Bowl and Drifter Bowl showed fragile cornices and wind slabs that would crack under the weight of a skier. Snowpit tests and probing in more sheltered areas did not reveal any signs of the mid December persistent weak layers. On Powderhouse Peak off of Luther Pass snowpit data and observations also did not reveal any signs of lingering persistent weak layers. In both of these areas the snowpit data as well as general observations indicated that the new snow has started to slowly consolidate and bond to itself and the old snow surfaces below it. 

As for as the previous deep slab issues, snowpit data and observations from Drifter Bowl, Powderhouse Peak, Red Lake Peak, Hidden Peak, and Becker Peak have all indicated that the persistent weak layer issues along the Sierra Crest have subsided. In the Mt. Rose backcountry tests conducted on 12/23 still showed a layer of old facets lurking near the base of the snowpack underneath the 12/10 rain crust on some NW-N-NE aspects in more sheltered terrain but not in other similar terrain. Those tests also indicated that actually getting enough force through that strong upper snowpack to break this layer would be extremely difficult and require a huge trigger like a giant cornice collapse, another very large avalanche, or maybe several people on a slope at once. These kind of large avalanches have become very unlikely and are becoming more and more unlikely with each passing day, but until we have more data on the changes in this layer, paying attention to where it may possibly exist and whether or not it may still have potential to let fractures travel through it still represents a prudent course of action.

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