Bulletin d’avalanche

Eastside Region

Eastern Sierra Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Drifting snow continues to build slabs on the surface and load buried persistent weak layers. You can trigger dangerous avalanches at any elevation today. Slabs can break unpredictably: failing mid-slope or in areas you may consider “safe.” Step back from steep slopes and areas with avalanche terrain overhead.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–3

    Snowfall and extreme wind over the past 24 hours have increased the stress on persistent weak layers. Wind continues to drift snow onto slopes with buried facets this morning. Faceted layers are responsible for shooting cracks, collapsing, and recent avalanches at all elevations. 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. Tracks on a slope are not evidence that it’s safe. Once triggered, these avalanches often break in unexpected ways and could involve the full depth of the snowpack. Choose travel routes with lower slope angles and without exposure to overhead hazards.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    West and Southwest winds reached speeds up to 100 mph overnight. Strong winds this morning are still depositing snow onto leeward terrain. As you gain elevation, you’ll likely find dense, spongy slabs getting larger and more sensitive. The most common places to trigger wind slabs will be the leeward sides of corniced ridgelines and the sidewalls of cross-loaded gullies. Due to the extreme wind speeds, unstable drifts may be found lower on slopes than usual and in unexpected places. Hollow-sounding drifts and shooting cracks through stiff or textured surface snow 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.

Avalanche Discussion

A skier near Mammoth Rock triggered an avalanche breaking on old snow yesterday. Forecasters near Minaret Vista experienced a collapse that rumbled over the terrain for up to 1000 feet. 

Friday: a rider was buried by a large avalanche that broke on weak snow near the ground and propagated across a steep, rocky slope below San Joaquin Ridge. Fortunately, their partner performed a quick rescue and there were only minor injuries. The same day, another party looks to have triggered a small avalanche below treeline while riding past on a snowmobile. Observers experienced collapses and shooting cracks near and below treeline on multiple aspects.

New loading has added stress to the fragile snowpack structure. 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. Warm temperatures yesterday stiffened the overlying slab. Because the weak snow is hidden below the surface the hazard can be hard to track. The consequences are potentially deadly.

Régions couvertes