Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
Vedi sulla mappa

Pericolo valanghe

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

In sintesi

Areas of wind drifted new snow and a buried weak layer in the upper snowpack continue to produce areas of unstable snow. Elevated concerns continue for avalanches triggered by backcountry travelers. Consider avoiding avalanche terrain on NW-N-NE aspects today.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2.5

    Ridgetop winds drifting new snow into unstable slabs remain a concern. Wind slabs that were formed during the past 24 hours were created by drifting during ESE winds. New wind slabs today will form by drifting during SW winds. This leads to the potential of encountering an unstable wind slab on any aspect today in near treeline or above treeline terrain. Some of the wind slabs on NW-N-NE aspect terrain may sit on top of buried surface hoar allowing for deeper failure and wider than usual propagation as a persistent slab avalanche.

    Due to the complexity of the current avalanche situation, simply identifying where the most recent wind drifting snow is depositing will not identify all of the slopes of concern. If you are determined to travel in avalanche terrain today, choosing E-SE-S-SW-W aspect terrain in wind protected areas below treeline has the lowest chance of triggering an avalanche at the current time.

    (3/20/2023)

    Avalanche on the N side of Roundtop Peak that involved the full burial and unlikely survival of a solo skier, Carson Pass area, CA. This avalanche was triggered in low angle terrain with connected steeper terrain above. Read the firsthand account.

    Photo: Public

  • Persistent Slabs

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

    This avalanche problem appears to exist mainly above 7,500' on NW-N-NE aspects where a layer of surface hoar exists on top of the uppermost crust in the snowpack. Two of the avalanches that occurred Monday were confirmed to have failed on this weak layer. Additional snowfall yesterday and today is gradually increasing the slab depth and continuing to provide stress to this weak layer. The distribution of the buried surface hoar layer is patchy, which makes it more likely to catch someone by surprise. Any persistent slab avalanches will have wider than usual propagation.

    Uncertainty around a persistent weak layer means that now is not a good time for aggressive terrain selection. Opting for non-avalanche terrain if traveling NW-N-NE aspects is highly recommended. The patchy distribution of the buried surface hoar makes it difficult to determine exactly which slopes or specific sections of larger slopes do or do not hold 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.

    (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

  • Long and short shooting cracks and test slope wind slab failures occurred yesterday.
  • 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. Most were wind slabs. At least two involved buried surface hoar.

Regioni coperte