Boletín de aludes

Central Sierra Nevada

Sierra Avalanche Center
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Peligro de aludes

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

Lo esencial

You could still trigger an avalanche today that fails 1 to 3 feet deep on top of weak old snow in the lower half of the snowpack. Carefully assess the snowpack before committing to avalanche terrain, especially in and adjacent to shaded areas. Signs of instability are becoming less obvious in some areas, making it easier to get caught by surprise in spots where instability lingers.

Problemas de aludes

  • Persistent Slabs

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

    Our persistent slab avalanche problem remains most prominent along the eastern side of the forecast area (Carson Range) above about 8,300' where evidence of instability is still reported daily. Fewer signs of instability have been observed along the Sierra Crest, but signs of unstable snow are showing up from time to time in areas near and above 8,900'.

    One of our longtime SAC Pro Observers summed it up well yesterday: "Informal obs did not indicate instability, but formal tests near 9000ft produced unstable results on the facets at the ground. This was a good reminder that without targeted, formal obs, we might have incorrectly assumed stable conditions".

    This is one of the reasons why a persistent slab problem on a decreasing trend presents a challenge that has fooled many seasoned backcountry travelers in the past. Signs of instability become less obvious and less frequent, and confidence builds right up until an avalanche is triggered unexpectedly.

    Utilizing different aspects or lower angle, non-avalanche terrain are options for minimizing exposure to this avalanche problem.

Avalanche Discussion

Weak faceted (sugary) snow crystals exist in the lower half of the snowpack on many NW-N-NE aspects above 8000 ft. The moisture content of this weak snow has increased, especially below 9,500'. Basal facets remaining dry post-storm have been observed in locations at 9,700' and 9,800'. In the Carson Range where the weakest snow was reported before the last storm, these moist to wet facets continue to fail in snowpack tests, and slope-scale snowpack collapses were reported on Tuesday and Wednesday. More time is needed before the persistent slab problem fully goes away despite the increases in weak layer moisture content.

Snow surface warming occurred across all aspects on Wednesday and Thursday. A crust has formed on the snow surface up to 8,300' and potentially higher in some areas due to recent fog.

The snowpack has become more usable, especially above 7,500'. There are still rocks to hit and open creeks to deal with, but not nearly as many as before this last storm.

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