Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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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 trigger a large avalanche breaking in layers of weak sugary snow hidden below the surface. Feedback like shooting cracks and collapses in the snowpack may not always be obvious. A smaller wind slab triggered in steep leeward terrain could step down to the buried weak layers. Your safest option is to limit yourself to low slope angles without avalanche terrain overhead.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Weak layers of sugary snow are responsible for shooting cracks, collapsing, and some recent avalanches at all elevations. In some areas, the feedback from these layers has been widespread and obvious, especially on north and east-facing slopes between Mammoth and June. In other places, you may not get signs of instability until you’ve wandered onto the wrong slope. Persistent slab avalanches can be triggered from low-angle terrain below or adjacent to avalanche starting zones. Once triggered, these avalanches often break in unexpected ways and could involve the full depth of the snowpack. Careful route selection and evaluation are important strategies to manage this problem. When in doubt, choose travel routes with lower slope angles and without exposure to overhead hazards.

  • Wind Slabs

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

    Some recent avalanches, below ridges and in steep couloirs, appear to have broken in wind-drifted snow. Observers yesterday noted light, low-density snow on slopes where west winds can come and move it onto leeward terrain. Winds are forecast at snow-blowing speeds today ahead of the next storm system. You may find new and recently drifted slabs on the leeward sides of ridgelines, in alpine couloirs, gullies, and cross-loaded depressions. Hollow-sounding drifts and shooting cracks through stiff or textured surface snow are signs that you have found unstable wind slabs. 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.

    (1/11/2024)

    Avalanche in the bottom of Bloody Couloir likely ran overnight on 1/10. Northeast aspect,  11, 000 ft.

    Photo: Clancy Nelson

Avalanche Discussion

Up to 14 inches of new snow fell with extreme winds Wednesday night. Over the last 48 hours, natural, explosive, and skier-triggered avalanches have run at all elevations near Mammoth. Some of these appear to have run mid-storm in wind-drifted snow. Others broke on buried weak layers. Forecasters near June Mountain triggered widespread, slope-scale collapses near treeline. Though natural avalanches are unlikely today, there is real potential for human-triggered avalanches large enough to bury or kill a person.

Recent and newly drifted snow can break in the upper snowpack on leeward slopes near and above treeline. A layer of sugary facets is buried around an old crust 1 to 2 feet below the surface. A fragile layer of large, loose, depth hoar exists near the ground on shady slopes. Both of these layers have been actively failing at the slope scale. Patiently choosing routes with low slope angles is the best way to mitigate your exposure to a hazard that is both unobvious and potentially deadly.

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