Boletín de aludes

Central Sierra Nevada

Sierra Avalanche Center
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Peligro de aludes

Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 11 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

UPDATED at 8:30 am.

CONSIDERABLE avalanche danger exists on NW-N-NE-E-SE aspects steeper than 35 degrees at all elevations with MODERATE danger elsewhere due wind slabs and storm slabs. Large human triggered avalanches that run long distances and involve large amounts of snow are likely today and natural avalanches may remain possible this morning. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential. Identify where wind slabs and storm slabs exist and avoid them and their run out zones.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    3

    UPDATE @8:30 am -- We have received reports of large natural avalanches that are ran long distances and hit the Alpine Meadows Road around 7:00-7:30 am. Other natural avalanches also occurred last night and early this morning. No details about what kind of avalanches these were or their failure layers are available. As mentioned below some similar natural avalanche activity may remain possible through this morning.   

    Strong winds and significant amounts of new snow at all elevations since 10 pm last night mean that wind slabs have formed on open slopes at all elevations. The largest and most fragile wind slabs will exist on exposed wind loaded near and above treeline N-NE-E aspects and cross loaded NW and SE aspects, but wind slabs could also exist in more sheltered locations and in below treeline terrain due to the strength of the winds during this storm. These wind slabs will continue to grow in size and extent today as the strong winds continue to move a combination of snow that fell last night and the new snow expected today. Even though the best window for natural wind slab avalanches likely occurred last night and early this morning, some natural wind slab avalanches may remain possible especially before noon today. Human triggered wind slab avalanches large enough to bury and injure people will be likely today on wind loaded slopes 35 degrees and steeper. These wind slabs will most likely fail on weaknesses within the new snow, but some could break on the old snow surfaces.

    Clues like cornices above a slope, blowing snow, wind drifted snow, ripples in the snow surface, and other wind created textures can help identify where wind slabs may exist. Using observations and clues like these to find where the wind slabs lurk and then avoiding those wind slabs represents a prudent choice for backcountry travel today.

  • Loose Dry

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

    Even though temperatures have gotten progressively colder since the snowfall started, some subtle temperature changes and rapid snow accumulation could have created some weaknesses within the storm snow like graupel layers or small density changes. In some cases failures on these weaknesses will manifest as small loose dry point release avalanches. However, these storm snow weakness will also allow human triggered storm slabs to become possible on open slopes steeper than 35 degrees in near and below treeline terrain where the new snow has more slab characteristics.

Avalanche Discussion

Yesterday observations from Powderhouse Peak on Luther Pass showed a strong, consolidated snowpack that should handle new snow loading well. The 1 to 2 inches of new snow that had already fallen in that area had already started to bond to the old snow surfaces that consisted of melt freeze crusts and moist snow on the sheltered northerly aspects and scoured crusts on the exposed aspects. Observations from other places around the forecast area this week have told a similar story with a well bonded snowpack capped by a a mix of melt freeze crusts, scoured surfaces, and old expoesed rain crusts.

UPDATE @8:30 am -- We have received reports of large natural avalanches that are ran long distances and hit the Alpine Meadows Road around 7:00-7:30 am. Other natural avalanches also occurred last night and early this morning. No details about what kind of avalanches these were or their failure layers are available.

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