Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

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

In sintesi

The storm has left unstable slabs of wind drifted snow and softer slabs of storm snow on steep slopes in both exposed and sheltered terrain. Recreating on slopes where these problems exist could trigger avalanches. Give the snowpack time to adjust to the new load before heading onto steep slopes. Plenty of nice snow exists on lower angle sheltered terrain. Expect CONSIDERABLE avalanche danger near and above treeline with MODERATE danger below treeline.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2

    Fresh slabs of wind drifted snow exist on wind-loaded and cross-loaded NW-N-NE-E-SE aspects. These wind slabs will remain fragile today. If people venture onto steep wind-loaded slopes, they will likely trigger wind slab avalanches. Wind slab avalanches could break several feet deep and could entrain enough snow to bury a person or maybe even a car. In some isolated areas, it is not impossible for these avalanches to break below the old snow surface on older weak snow. Sun on wind-loaded slopes could make wind slabs easier to trigger. Large fragile cornices also lurk above many wind-loaded slopes.

    Look out for cornices above a slope, convex pillows of wind-drifted snow, scoured ridgetops, and wind created surface textures. Use this information to plan a route to avoid areas where dangerous wind slabs may lurk. Soft cold snow will exist in abundance on lower angle slopes in areas sheltered from the wind.

  • Loose Dry

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

    People recreating on steep slopes in sheltered terrain could still trigger avalanches that involve slabs of storm snow 1 to 2 ft deep. These storm slab avalanches could entrain enough snow to bury a person. They could break on weaknesses within the storm snow or may fail on the old snow surfaces. In some isolated areas, they may overload weak layers below the old snow surface. Similar to the wind slabs above, sun on slopes could make storm slabs easier to trigger.

    Since the new snow may look soft and smooth, storm slabs can be hard to identify. Recent avalanche activity, shooting cracks, and test slope failures can all help identify which slopes may hold unstable storm slabs. Storm slabs tend to gain strength relatively quickly so being patient and waiting a couple of days to travel on steeper slopes can also help avoid the storm slab problem. 

     

Avalanche Discussion

Yesterday morning skiers triggered storm slab avalanches in Munchkins that measured about 6 inches in depth. Later in the day, skier-triggered storm slabs on test slopes on Silver Peak (mid-day) and Trestle Peak (afternoon) measured 12 to 18 inches in depth. On Silver Peak, the storm slabs failed just above the old snow surface and on Trestle Peak they failed just below the old snow surface. Observers also reported upside-down layering and skier triggered shooting cracks in the storm snow on Pickett Peak. Small storm slab activity that occurred Saturday evening was also reported from near Frog Lake Cliffs (near Castle Peak).

A small wind loaded test slope on Silver Peak released as a skier approached the slope yesterday. Observers also reported widespread cracking on wind drifted test slopes on Powderhouse Peak. Small wind slab avalanches that occurred on Saturday evening were also reported on Andesite Peak. 

Skier triggered loose dry sluffs occurred before 10 am yesterday in Deep Creek.  

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