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 8 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Some wind slabs may exist on top of a buried weak layer in some areas in very wind-exposed near and above treeline terrain. The avalanche danger is MODERATE. Human triggered avalanches may be possible today.

Problemi valanghivi

  • Wind Slabs

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

    Firm sun crusts on many windward slopes and moderate wind speeds limited wind slab formation to the most wind-exposed NW-N-NE-E aspects in near and above treeline terrain. In some cases, these wind slabs formed on top of weak feathery snow known as surface hoar. Some wind transport and wind-loading could continue today in isolated areas particularly if any new snow accumulates. Most avalanches resulting from these wind slabs should remain small. Small avalanches can have serious consequences especially with all the rocks and obstacles lurking near the snow surface. It is not impossible for a wind slab avalanche to involve enough snow to bury or injure a person (size D2) in some areas. 

    Signs that wind slabs may exist on a slope include cornices above a slope, wind drifts/pillows, ripples/wind-created textures on the snow surface, hollow sounding firm snow, and current blowing snow. The buried surface hoar will make any wind slabs that do exist more difficult to manage. Surface hoar can allow remote triggering of avalanches and can allow avalanches to propagate across wider areas and run farther downslope. If there are any doubts or uncertainty about the existence of an unstable wind slab on a slope, assume the slope is unstable and avoid it. Avoiding wind-loaded terrain where problematic wind slabs may linger represents a great way to manage today's potential avalanche problem and to enjoy the cold soft snow that still remains in many more-sheltered, non-wind-exposed areas.

Avalanche Discussion

* Along the upper elevation ridgelines and in very exposed near treeline areas small fragile wind slabs and new cornices were observed in the area between Castle and Basin Peak yesterday. Ski cuts caused shooting cracks and small wind slab failures on wind-loaded test slopes. No wind slab formation was seen at lower elevations or in less exposed terrain.

* Widespread wind scouring had occurred on the windward aspects on Castle Peak. Firm sun crusts had also formed on the sun-exposed aspects on Castle Peak, Basin Peak, Tamarack Peak, and Andesite Peak. Both of these factors helped limit wind transport.

* Widespread surface hoar existed on shaded sheltered slopes in the Donner Summit and Mt. Rose areas.

* Decent snow coverage exists above 7,000' to 7,500' along the Sierra Crest with the best coverage in the northern and far southern Sierra Crest portions of the forecast area.  Snow coverage declines to the east. Early season conditions exist.

** Vague reports of a skier incident on Tallac yesterday came in this morning, but no details concerning whether or not it was an avalanche incident or a fall exist. If we get information that it was an avalanche incident, we will update the site. 

 

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