Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You could still trigger an avalanche where stiff wind drifts break over a weak base of loose surgery snow. Thin coverage, with rocks and logs poking through the snow, increases the consequences of getting caught in an avalanche. Carefully assess the snowpack before stepping out onto cold, shady slopes steep enough to slide.

Problemi valanghivi

  • Persistent Slabs

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

    In isolated areas, recent storms built a slab of wind-drifted snow over weak layers of facets and depth hoar at the base of the snowpack. The problem is most likely found on 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: cold, shady, leeward slopes. 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

Several small loose dry avalanches sluffed down steep northerly slopes over the weekend.

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. 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 wind-stiffened slab is more continuous. The snow atop the weak layer varies from a few inches of loose cold snow to stiff slabs more than a foot thick. Warm temperatures 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, which could make the persistent slab problem more widespread.

A rain crust below about 9500 feet has left the snowpack more supportable at lower elevations. However, thin coverage and shallowly buried rocks and logs deserve special attention. 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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