Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Some human-triggered wind slab avalanches may remain possible where strong shifting winds have left firm slabs of wind drifted snow near ridgelines, in gullies, and on open slopes exposed to the wind. Widespread firm icy conditions present additional hazards today including long sliding falls. MODERATE avalanche danger exists in near and above treeline terrain with LOW avalanche danger below treeline. Factor both the avalanche concerns and challenging snow conditions into today's travel plans.

Problemi valanghivi

  • Wind Slabs

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

    Strong NE winds have been blowing snow across the ridges since yesterday. The wind should shift back to the W today and may move some of that snow back to the other side of the ridges. This back and forth has left stiff slabs of wind drifted snow and areas of firm wind-scoured surfaces on a variety of aspects. Most of the wind slabs should remain small and not extend very far away from ridgelines. However, a few of them may be large enough to cause problems for backcountry travelers especially when combined with the firm and icy surfaces that exist in many areas. Triggering a wind slab avalanche may still be possible in some places today.

    Today's travel plans should account for the possible wind slabs and potentially challenging snow surface conditions. Blowing snow, cornices above a slope, wind pillows, and areas of smooth, firm, hollow-sounding snow can help identify where a wind slab may exist. Monitoring the snow conditions and talking about them with your group can help avoid traveling into an area where conditions exceed your group's abilities or comfort levels. Making the choice to turn around or change plans to use more mellow terrain can sometimes feel disappointing, but often it represents one of the smartest and most fun decisions.

Avalanche Discussion

Variable snow conditions have made backcountry travel challenging. A widespread rain event combined with strong NE winds has left firm icy surfaces on many slopes. A fall on one of these could easily result in a long uncontrollable slide. In areas where the crust is thinner, breakable crust conditions exist. Wind-hammered, variable, uneven and firm surfaces exist in the few places where the rain crust is absent.

* Observers reported NE winds blowing snow and loading W-SW aspects of Tamarack Peak (Mt Rose backcountry), Freel Peak (S of Heavenly), and Castle Peak (Donner Summit) yesterday. Some small, shallow wind slabs that did not extend very far away from the ridges had also formed on these aspects.

* Rain crusts extended to the top of Castle Peak at 9000 ft and the top of Freel Peak at 10,800 ft. This rain crust was reported at the summit of the West Shore and upper elevations on Carson Pass as well.

* Observations in the Tamarack Peak area yesterday found widespread wind effects and variable snow surfaces ranging from firm wind-buffed snow to breakable wind crusts to shallow soft snow on top of supportable snow in the most sheltered areas. In this area, a dense layer of supportable snow existed at or near the surface but the rain crust seen on the Sierra Crest was not observed above 8800 ft.

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