Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
Open full map
Non aggiornato — questo bollettino è scaduto 13 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Near treeline and above treeline, avalanche danger is HIGH on NW-N-NE-E-SE aspects on slopes 32 degrees and steeper. For all other areas, avalanche danger is CONSIDERABLE on slopes 32 degrees and steeper. Wind slab, storm slab, wet slab, loose wet, and deep persistent slab avalanches are all possible today.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    3

    New snow and wind transport last night has further increased the size of wind slabs that existed over the past several days. Winds slabs 2 to 4+ feet or more thick now exist near treeline and above treeline on NW-N-NE-E-SE aspects. Large destructive avalanches are possible today. Some of these wind slab avalanches could take on wet slab characteristics today in areas where the slab becomes wet from rain due to rising snow levels.

  • Loose Dry

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

    New snow has deposited on top of weak layers of buried surface hoar, buried graupel, near crust facets, and/or lower density storm snow layers that are known to exist within the upper snowpack between the Jan 30 rain crust and the snow surface. Human triggered avalanches are likely and natural avalanches are possible near treeline and below treeline on NW-N-NE-E aspects above 7,000'. Warming air temperatures today will deposit higher density new snow on top of lower density new snow creating an upside-down snowpack. This will further serve to increase snowpack instability in these areas. Some of these storm slab avalanches could take on wet slab characteristics today in areas where the slab becomes wet from rain due to rising snow levels.

  • Loose Wet

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

    As snow levels continue to rise today, rain will fall on new snow. Loose wet avalanches are possible, below 7,000' to 8,000' on all aspects. Wet loose avalanches are most likely to initiate on slopes 37 degrees and steeper.

Avalanche Discussion

Observations made yesterday along the Blue Lake Road (Carson Pass area), in the Deep Creek drainage, and on Andesite Peak (Donner Summit area) all revealed unstable wind slabs. Wind slabs ranging from 4 inches to 2 feet thick were observed in wind loaded areas on NW-N-NE-E aspects in near treeline and above treeline terrain. Intentionally skier triggered avalanches occurred in Deep Creek and on Andesite Peak. These wind slabs were noted to fail on lower density layers of snow between the base of the wind slab and the top of the prominent January 30 rain crust. The exact failure layers of these avalanches and other observed unstable winds slabs varied from one location to another. Near crust facets, buried surface hoar, and simple lower density layers of storm snow associated with rising snow levels over the past few days are all likely culprits. Blowing snow at the sites of the noted instabilities made exact snow crystal type very difficult to identify

In areas above 9,500' deep persistent slabs linger near treeline and below treeline on NW-N-NE aspects. Weak layers of well developed facets and depth hoar remain buried in the snowpack in these areas and were not destroyed by rain on January 28 and 29. The likelihood of failure of these basal facets will increase as this storm cycle progresses and additional new snow load stresses the snowpack above these weak layers. Locations that are both above 9,500' and near treeline or below treeline terrain represent only a small portion of the forecast area, keeping this problem isolated in distribution.

Regioni coperte