Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

HIGH avalanche danger will occur today for all elevations. An avalanche warning is in effect through 7 am Friday. Travel in or below avalanche terrain is not recommended. If you choose to go out into the backcountry today, please create and closely follow a clear and detailed plan to travel only on slopes less than 30 degrees in slope angle without any exposure to steeper terrain above. Poor visibility may make navigation and terrain recognition very difficult.

Problemi valanghivi

  • Wind Slabs

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

    Feet of new snow combined with wind transport today and tonight will create widespread areas of large unstable wind slabs mainly near and above treeline on NW-N-NE-E-SE aspects. In more isolated areas wind slabs could form below treeline due to the strong to gale force winds and the duration of this storm event. Potential avalanche size is expected to quickly reach D2 to D3 today with isolated size D4 possible as the storm progresses*.

    Avalanches could be long running and move through mature stands of trees on the valley floor. Travel in or below avalanche terrain is not recommended. Identify and avoid avalanche terrain. Poor visibility may not allow for the proximity to avalanche terrain to be recognized without the proper use of map and compass, gps, etc.

    *Avalanche size D2 could bury, injure, or kill a person. Avalanche size D3 could bury and destroy a car, damage a truck, destroy a wood frame house, or break a few trees. Avalanche size D4 could destroy a railway car, large truck, several buildings, or a substantial amount of forest.

  • Loose Dry

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

    High intensity snowfall with accumulation rates of 2+ inches per hour will cause rapid loading in wind protected areas. This will lead to storm slab development in near treeline and below treeline areas on all aspects. Potential avalanche size is expected to reach D2 to D3.

    Travel in avalanche terrain is not recommended. Avalanches initiating in open areas below treeline or in areas of widely spaced trees could run significant distances through forested terrain. In order to anchor the snowpack in place, trees will need to be too closely spaced to travel thorough on skis or a snowmobile. Simply "staying in the trees" may not be a successful tactic for avoiding avalanches today. Slope angle is the critical factor.

     

  • Storm Slabs

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

    Throughout the forecast area on near treeline and below treeline NW-N-NE aspects, a layer of faceted snow was observed around 1 foot below the snow surface prior to the start of the current snowfall event. In isolated areas, snowpits tests have clearly indicated that this layer will not respond well to rapid new snow loading. Failure of this layer will lead to deep slab avalanches.

    As this storm progresses and wind slabs and possibly storm slabs will exceed 3 feet in slab thickness, these avalanche problems could take on deep slab characteristics (failing deeper, wider, and more destructive than typically anticipated) and not necessarily triggered by the first person on the slope. Travel in avalanche terrain is not recommended.

Avalanche Discussion

* Several wind slabs avalanches were reported this past week from around the forecast area. More details are available in the specific observations section of this website.

* A potentially problematic layer of old near surface facets and/or near crust facets has been observed throughout the forecast area near treeline and below treeline on NW-N-NE aspects. This layer had around 1 foot of snow on top of it prior to the start of this storm. In isolated areas, snowpit tests have indicated that this layer will react poorly to rapid new snow loading.

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