Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 9 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

MODERATE danger continues in near and above treeline terrain where hard wind slabs exist above older weaker snow. While these hard slabs may be difficult to trigger, human-triggered avalanches remain possible. If these slabs do break, they would likely fail above the trigger or after that person committed to the slope. Identify where wind slabs exist and avoid them. Firm or icy surfaces where arresting a fall would be challenging also exist on some exposed near and above treeline terrain.

Problemi valanghivi

  • Wind Slabs

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

    Stubborn, hard wind slabs exist above a layer of loose weak snow (facets) on some wind-loaded NW aspects. These conditions may also exist on some wind-loaded N-NE aspects where the NE winds have not scoured away the wind slabs. These wind slabs exist in specific areas in near and above treeline terrain near ridgelines and have grown up to 18 inches in depth. Triggering these wind slabs may be difficult due to the strength of the slab, but it is possible for larger triggers like large cornices or multiple people on a slope or even the right trigger in the right place to cause an avalanche. If they do break, these hard wind slabs would likely break above the person who triggers them or break after the person on the slab has already committed to the slope. Areas where a shallower wind slab exists, places near exposed rocks, convex rollovers, and unsupported slopes could represent some of the trigger points where breaking one of these hard slabs may be easier.

    Use clues like blowing snow, hollow sounding snow, cornices above slopes, drifted snow, ripples in the snow surface, and other wind created textures to identify where wind slabs may exist and avoid those areas. Travelling in sheltered non-wind-affected terrain where softer snow still exists should provide safer and more enjoyable conditions today. 

Avalanche Discussion

* Hard wind slabs resting above a weaker layer of older snow (facets) exist on wind-loaded NW aspects of Andesite Peak and Castle Peak. Tests targetting these stubborn, hard wind slabs yielded unstable results in both places on Tuesday and Wednesday (ECTP's and 2m ECTP's).

* Whumphing and cracking occurred yesterday in Munchkins east of Alpine Meadows on N-NE aspects near treeline where wind slabs existed.  

* Widespread firm, icy, scoured surfaces or hard wind packed surfaces exist on exposed N-NE-E aspects.

* Some areas of soft, unconsolidated snow still exist on near and below treeline northerly aspects sheltered from the E and NE winds, but the snow surface conditions are becoming more variable.

Snow coverage is deepest in areas above 8000 ft. in the northern half of the forecast area (north of Emerald Bay). Even at these elevations, snow coverage varies by location. Some areas at the upper elevations south of Emerald Bay still have marginal snow coverage. Below 8000 ft. most areas still have patchy snow coverage with many exposed obstacles and areas of bare ground. 

Regioni coperte