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
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 10 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

CONSIDERABLE avalanche danger at all elevations exists today, increasing to HIGH danger this evening. Human triggered avalanches are likely and natural avalanches are possible. A complex mix of wind slab, storm slab, and deep slab avalanche problems exist. The majority of avalanche activity today is expected on slopes 35 degrees and steeper but could occur on slopes 30 degrees and steeper in isolated areas. An Avalanche Warning has been issued starting 4 pm today lasting through 7 am Thursday.

Problemi valanghivi

  • Wind Slabs

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

    Human triggered wind slab avalanches occurred yesterday in a variety of locations. The ongoing combination of new snow and wind will keep this problem ongoing today. This problem will be most prevalent on NW-N-NE-E-SE aspects in near treeline and above treeline areas, but could be found in more isolated areas on other aspects or below treeline.

    Numerous clues such as drifting snow, cornices, and wind pillows exist to identify areas of recent wind loading and subsequent wind slab formation. Identify and avoid areas where wind slabs are likely to exist.

  • Loose Dry

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

    New snow from this storm cycle continues to accumulate and is now measured in feet in the majority of locations. Snowpack failure associated with this problem is possible at the old/new snow interface on old near surface facets or anywhere within the storm snow. With warming air temperatures, the storm snow is expected to become increasingly upside down. This avalanche problem will be most prevalent in wind protected near treeline and below treeline areas on all aspects.

  • Storm Slabs

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

    As new snow continues to increase the load on the snowpack, large persistent slab trending to deep slab avalanches are an increasing concern. The problematic weak layer of near crust facets on top of the Dec 15 rain crust is now buried 2 to 4+ feet deep in the snowpack. Any avalanches that either initially fail on or step down to this weak layer will be large and destructive. Recent snowpit data has shown increasing variability on the degree of weakness in this layer from one location to another, but it is still a problem. This problem is possible on W-NW-N-NE-E aspects above about 7,200', regardless of proximity to treeline.

Avalanche Discussion

Human triggered wind slab avalanches occurred yesterday on Elephant's Hump (Carson Pass area) and in numerous areas on Castle Peak (Donner Summit area). Avalanche activity was noted to occur either at the old/new snow interface or within the storm snow. On Waterhouse Peak (Luther Pass area), significant blowing snow was observed in open areas near treeline. Areas of wind load that existed yesterday around the forecast area were noted to range from 8 inches to 4 feet. Last night's snowfall will have made these areas even more loaded. Recent snowpit data targeting the persistent weak layer of Dec 15 near crust facets has shown increasing variability in weakness of this layer, but unstable test results continue to occur.

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