Bollettino valanghe

Central Sierra Nevada

Sierra Avalanche Center
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Pericolo valanghe

Thu
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

Unstable slabs of wind-blown may still exist near ridges, below cornices, in gullies, and on steep open slopes. Sunny slopes could also get warm enough for wet snow to slide downhill. Be willing to change plans and move to gentler terrain if you see signs of unstable snow.

Problemi valanghivi

  • Wind Slabs

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

    Unstable wind slabs may linger in areas where the wind has piled snow up over the last few days, especially on slopes near ridges, in gullies, or complex or extreme terrain. Due to the changing wind directions, wind slabs could exist on almost any aspect. In some places, the winds may have stiffened existing wind slabs into hard slabs that can break above a person. Today's warmer weather and intense sunshine may weaken some wind slabs on slopes with full sun exposure, like cross-loaded SE-facing gullies. 

    Shifting winds have scoured and loaded some slopes, making identifying which slopes still hold wind slabs harder. Assume the wind slab problem could exist on any exposed slope. Watch out for slopes with cornices above them and slopes with firm hollow-sounding snow or dense wind-packed snow on top of softer snow. 

    (4/4/2023)

    Large cornices above NE and N facing slopes on Tamarack Peak

    Photo: SAC

  • Loose Wet

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

    While cloud cover this afternoon may block some of the sun's intensity, above-freezing daytime highs combined with April sunshine could still provide enough warming for areas of unstable wet snow to form. Initial signs of wet snow problems include rollerballs and pinwheels. These could progress to sluffs of wet loose snow that entrain more snow as they slide downhill, especially on sunny E-SE-S-SW-W facing slopes steeper than about 35 °. Smaller amounts of wet snow may also form on NE and NW aspects due to the higher sun angles this time of year. 

    Signs that the snow has become wet enough for wet loose avalanches include rollerballs, pinwheels, and other wet loose avalanches. Once the snow gets wet enough to slide downhill, moving to slopes less steep than 35 ° or to different aspects where the snow has not warmed up can help reduce the risk of encountering a wet loose avalanche. 

    (3/30/2023)

    Roller balls formed around noon in sun exposed terrain, Donner Summit, CA.

    Photo: SAC

Avalanche Discussion

  • Fewer signs of wind slab instability were reported yesterday, but people still triggered shooting cracks in wind-loaded test slopes. Most of the sunny days in March have seen human-triggered wind slabs, and several close calls have occurred this spring.
  • Large cornices exist along many ridgelines. Some of them have deep cracks behind them. 
  • Signs of persistent instability on old weak layers across NW-N-NE aspects within the forecast area have become increasingly isolated even though tests can still identify some of these layers. Triggering an isolated persistent slab avalanche has become unlikely on a regional scale but may not be impossible.

Regioni coperte