Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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4 · Forte
Limite del bosco
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In sintesi

UPDATED @ 1:30PM 

Due to snow levels rising sooner than expected, natural and human triggered avalanches are likely this afternoon and tonight. Large destructive deep slabs, wind slabs, and wet slabs that run long distances are likely as more rain and snow impact the region. Very dangerous avalanche conditions exist. Travel in or near avalanche terrain is not recommended. The avalanche danger has increased to HIGH at all elevations due to rain, wind, and snow impacting the region.

Problemi valanghivi

  • Wind Slabs

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

    New wind slabs will form on wind loaded W-NW-N-NE-E-SE aspects in near and above treeline terrain steeper than 35 degrees today as more snow and wind impact the forecast area. The heavy wet snow that comprises these wind slabs may not bond to the current snow surfaces and human triggered wind slabs will become likely during the day and natural and human triggered wind slabs could become likely overnight. These new wind slabs could involve 2 to 3 ft. of wind loaded snow in some places by this afternoon, and they will continue to grow in size overnight and during the next 36 hours in places above snow line where more snow accumulates. They could also step down and become the deep slabs mentioned below.

  • Storm Slabs

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

    More snow and rain during this storm will add significant load to the snowpack and make it easier for the facets near the 12/15 rain crust to fail. If this layer does fail, large destructive deep slab avalanches will result. These human-triggered deep slab avalanches remain possible today throughout the entire forecast area on W-NW-N-NE-E aspects at all elevations. As more snow and rain continue to load the snowpack over the next 36 hours, natural and human triggered deep slab avalanches will become likely. These slabs could measure anywhere from 4 to 10+ feet deep. Rain on snow could also trigger deep wet slabs on this layer in the next 36 hours.

    Deep slabs are unpredictable. Remote triggering with large propagation into any connected terrain remains possible. Large to historic runout zones could occur if a deep slab avalanche was triggered. Ski tracks on a slope will not be an indicator of stability and steep trees will not be a safe zone. Avalanche avoidance and cautious route finding remain the best practice to deal with this deep slab avalanche problem. Deep slabs can occur on less steep slopes and any slopes steeper than 30 degrees are suspect. 

  • Persistent Slabs

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

    UPDATE @ 1:30 pm:

    Snow levels have climbed to above 8000 ft. in most of the forecast area. Where rain is falling on snow, wet slabs and loose wet avalanches are now likely. As more rain loads the snowpack some wet slabs may step down to the deep slabs mentioned above.

    Previous Description published @ 7:00 am:

    Heavy wet snow on top of cold light snow means that human triggered storm slabs will be possible today. As more heavy snow accumulates during the storm, human triggered and natural storm slab avalanches will become likely. As the snow changes to rain, rain on snow could also cause widespread avalanche activity. These wet storm slabs could also step down to become deep slabs mentioned above and could occur on slopes steeper than 30 degrees where new snow or rain falls. 

Avalanche Discussion

Yesterday observations in Deep Creek, on Andesite Ridge, and on Red Lake Peak all showed settlement and consolidation in the upper snowpack. Snowpit data from Deep Creek and Andesite ridge revealed that the facets near the 12/15 rain crust remain weak and that fractures can still travel through that layer. In Deep Creek, a whumph occurred on that layer while excavating the pit. Another party in Deep Creek reported some shooting cracks in wind loaded areas. A party on Herlan Peak (east shore) reported large whumphing on N-NW slopes. Ski kicks on wind loaded test slopes on Red Lake Peak and Andesite Ridge as well as a cornice dropped onto a test slope on Andesite Ridge did not trigger signs of instability on wind loaded test slopes. Several other recent avalanches that likely failed on the 12/15 facets on Wed. or Thurs. were also reported from areas including Andesite Ridge, Castle Peak, and Deep Creek. Ski areas also reported still being able to trigger this layer with very large triggers yesterday. 

PREVIOUS BOTTOM LINE PUBLISHED AT 7:00AM

Human triggered avalanches will become likely again today. Deep slabs, wind slabs, and storm slabs represent today's avalanche problems. Natural and human triggered avalanches will become likely by tonight as the storm continues. Large destructive avalanches could occur. Rain on snow could trigger widespread avalanche activity. CONSIDERABLE avalanche danger exists at all elevations today and the avalanche danger will rise to HIGH tonight or sooner if the snow level rises faster than expected.

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