Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

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

In sintesi

Additional snowfall today with increasing winds will create slabs of wind drifted snow in exposed areas.  In addition, a buried weak layer in the upper snowpack could still produce unstable snow.  Look for signs of instabilities while traveling in the backcountry and be willing to change plans if you encounter unstable snow.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Increasing SW winds today with additional snowfall will create blowing snow and new wind slab development on NW-N-NE-E-SE aspects in near and above treeline areas.  Existing soft snow exists for wind transport as these SW winds began to increase in speed early this morning.  Wind slabs that form on NW-N-NE aspects above a layer of buried surface hoar could create deeper and wider propagating avalanches that have persistent slab avalanche characteristics. 

    Look for blowing snow, new cornice formation, wind pillows, and snow surface scouring as clues to where these wind slabs are forming.  Make a plan that accounts for the current avalanche problems and where in the terrain they could exist.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    A layer of surface hoar was buried on Sunday March 19 during a storm event.  Multiple avalanches were reported on Monday, some of which were confirmed to be failing on this buried surface hoar layer.  Other avalanches that occurred that day are thought to have failed on this layer due to the wide propagation and some remote triggering of these avalanches.  In some areas of the forecast region, the Sunday storm had rain or wet heavy snow that destroyed some of this surface hoar layer, potentially up to around 7500'.  Recent observations targeting this layer have found it to be patchy in distribution with variable weakness in snowpack tests.  Additional snowfall over the last couple days and today is gradually increasing the slab depth and continuing to provide stress to this weak layer. 

    Recent wide propagating avalanches, unstable snowpit test results, snow surface cracking, snowpack collapse, or whumpfing are all signs of unstable snow in the area.  The patchy nature of buried surface hoar make it very challenging to manage in the backcountry.  If traveling on NW-N-NE aspects, sticking to slopes under 30 degrees in steepness with no overhead hazard may be the best strategy until this weak layer gains strength.   

    (3/20/2023)

    An unintentional snowboarder triggered avalanche on the N side of Castle Peak. Buried surface hoar confirmed as the failure layer. Donner Summit area, CA

Avalanche Discussion

  • Numerous avalanches in the size D1 to D2 range were triggered Monday by backcountry travelers on N to NE aspects in the Donner Summit, West Shore Tahoe, and Carson Pass areas.  At least two avalanches involved buried surface hoar.

Regioni coperte