Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

You could trigger an avalanche where a stiff slab rests over a weak layer of loose surgery snow. Carefully assess the snowpack before stepping out onto cold, shady slopes steep enough to slide. Thin coverage, with obstacles poking through the snow, increases the consequences of getting caught in an avalanche.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    In isolated areas, a slab of stiffer snow overlays weak facets around a buried crust, or at the base of the snowpack. The problem is most likely found on cold, shady aspects and terrain features prone to wind-loading, which had continuous snow coverage in November and early December. Persistent weak layers are slow to gain strength and can remain a concern over an extended period.

    If you find a dense layer of snow with weak sugar underneath, you’ve found the ingredients for a persistent slab. If triggered, the resulting avalanche could break in unexpected ways involving the full depth of the snowpack. When in doubt, you could avoid steep terrain where the problem might exist. Shooting cracks and whumpfing noises in the snowpack are signs of instability.

    (12/24/2023)

    This avalanche failed on buried facets and likely ran on 12/21

    Photo: Clancy Nelson

Avalanche Discussion

The last reported slab avalanches likely ran on the 21st, during the last windy storm. These failed on weak facets buried under wind-drifted snow. While the snowpack is slowly gaining strength, every observation since December 19th has included signs of instability, like cracking or collapsing of the snowpack as a result of the same poor structure. 

Across the majority of the forecast area, avalanche start zones with enough snow to be concerning are isolated. The exception is the Mammoth Lakes area, and closer to the Sierra Crest. In these areas, the combined distribution of weak layers and an overlying slab is more continuous. The snow atop the weak layer varies from a few inches of loose snow to stiff slabs more than a foot thick. Warm days and sunshine have melted the snow surface near and below treeline leaving some areas crusty. Rising temperatures may consolidate loose surface snow into a slab, meaning you could find more slopes where the problem exists.

On lower elevation slopes still holding snow, a rain crust below about 9500 feet has left the snowpack more supportable. However, thin coverage, with shallowly buried rocks and logs, is a major hazard. Walking or skinning downhill may be a good option if your planned descent is less ridable than it appeared from afar.

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