Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 8 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

MODERATE avalanche danger exists in near and above treeline terrain with LOW danger in below treeline areas. Lingering wind slabs and unlikely but not impossible deep slabs represent today's avalanche problems. Human triggered avalanches may still remain possible in some areas.

Problemi valanghivi

  • Wind Slabs

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

    Strong SW winds during the storm and strong NE winds after the storm have left a mix of firm wind slabs, soft wind slabs, and scoured surfaces on most wind-exposed aspects. In areas where wind slabs exist, human-triggered wind slabs could still be possible. The newer wind slabs formed by the NE winds will remain more sensitive, but they should also be smaller and involve less snow. The older wind slabs formed by the SW winds could be larger but should be more difficult to trigger. 

    Cornices above a slope, blowing snow, hollow sounding firm snow, and other wind created features can help identify where wind slabs and wind scoured/affected surfaces may exist. Choosing slopes sheltered from the wind could provide better snow conditions and fewer avalanche concerns. 

  • Storm Slabs

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

    Strength gains in the persistent weak layers 4+ ft below the surface and the strong snow above those layers has made triggering a deep slab avalanche unlikely. Still, this problem may not be impossible in an isolated area where conditions are just right or with a large enough trigger (large cornice failures, multiple people on a slope, etc). Complex terrain with steep cliffy areas, overlapping avalanche paths, unsupported slopes, and lots of trigger points could represent some of the isolated areas where a surprise might still happen.

    Some uncertainty still surrounds this problem. Pay close attention to areas where these old layers may exist especially in complex terrain when there is a potential for a large trigger to impact the slope. Good group management techniques like traveling one at a time from safe zone to safe zone and plans that provide buffer zones around suspect terrain could help create appropriate safety margins.

Avalanche Discussion

* Observations from Trimmer Peak and Relay Peak found some signs of instabilities around small wind slabs on exposed upper elevations slopes. On Relay Peak cornices remained fragile but refrigerator sized cornice blocks dropped onto a wind-loaded slope did not trigger larger wind slabs. 

* Wind-scoured surfaces existed on ridgelines and on the upper portions of NE wind exposed slopes on Red Lake/Stevens Peak, Trimmer Peak, Angora Peak, Relay Peak, and on Silver Peak. In some areas, the wind scouring had brought the rain crust to the surface. Observers also noted blowing snow in some upper elevation areas near Trimmer Peak and on the Sierra Crest north of Silver Peak. 

* Below the ridges on Trimmer Peak, Red Lake/Stevens Peak, Angora Peak, Silver Peak, and Relay Peak wind effects decreased dramatically and soft unconsolidated snow existed on northerly aspects with some slightly sun affected snow on southerly aspects. 

* Snowpit data from Silver Peak targetting the deeply buried surface hoar and old facet layers yielded similar results to data from Hidden Peak on Monday and indicated that these old persistent weak layers continue to gain strength.

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