Boletín de aludes

Eastside Region

Eastern Sierra Avalanche Center
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Peligro de aludes

Fri
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
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

In the past 48 hours light snowfall and wind-loading caused a natural avalanche cycle involving weak layers at the base of the snowpack. With a break in the weather signs of instability may become less obvious, but there is still a good chance of triggering a large avalanche failing at the base of the snowpack. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2.5

    Human-triggered avalanches breaking at the base of the snowpack remain likely. We are still within the first forty-eight hours following a peak in instability and the current persistent slab problem has shown that it gains strength very slowly following increases in natural avalanche activity. Variation in snow depth near and above the treeline has led to larger slabs with weaknesses at their margins and around trigger points in shallower areas. If triggered, the resulting avalanche could break with little warning, involving the full depth of the snowpack. Persistent slab avalanches can be triggered from below a steep slope or from adjacent slopes. These avalanches can propagate long distances and beyond terrain features that typically contain surface instabilities such as storm or wind slabs. Managing this problem is made more difficult because of our shallow and inconsistent snow coverage. The few areas with enough snow for backcountry riding are generally the same areas where the avalanche problem exists. To limit your exposure to persistent slab avalanches look for travel routes with slope angles less than 30 degrees and without overhead hazard.

    (1/17/2024)

    Large natural avalanche, NE aspect, 10,800', Mammoth Lakes Basin. Released overnight between 1/16/24 and 1/17/24.

    Photo: Everett Phillips

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    In the northern part of the forecast area reactive wind slabs were found near and above the treeline yesterday. Be cautious around steep terrain features that encourage drifting, such as the leeward sides of ridgelines, alpine couloirs, gully features, and cross-loaded depressions. Hollow-sounding drifts, shooting cracks through stiff or textured surface snow, and the snowpack collapsing under your weight are indications that you have found unstable wind slabs. Keep in mind that even a relatively small wind slab avalanche breaking in the upper snowpack may be enough to step down to persistent weak layers near the ground, creating a larger avalanche involving the full depth of the snowpack.

    (1/16/2024)

    Natural activity likely occurred overnight on 1/16/24

    Photo: Steve Mace

Avalanche Discussion

Recent avalanche activity: Multiple natural wind slab and persistent slab avalanches released on N and NE aspects near and above treeline overnight on 1/16 to 1/17. 

Snowpack Summary: There are currently three layers of concern in the snowpack: (1) Storm interfaces within or at the bottom of the most recent snow down 10 to 20cm from the surface; (2) a  layer of small to medium-grained facets down 40 to 90 cm; and (3) advanced facets and depth hoar buried near the ground down 60 to 120cm.  Any of these layers may become the primary layer of concern depending on aspect, elevation, and wind-loading patterns. Digging and probing as you travel through terrain will help to track the presence and depth of these layers. 

There are two main sources of uncertainty in today's forecast; (1) Persistent slab avalanche forecasting is inherently uncertain. (2) With lower-than-normal snow coverage this season there have been fewer observations from a limited number of backcountry areas. 

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