Bollettino valanghe

Central Cascades

Central Oregon Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Heavy snowfall and strong winds will create dangerous avalanche conditions at treeline and above.  Wind Slab avalanches will be likely on any North and East facing slopes that the wind has blown snow onto.  Often strong winds can create wind compacted snow (and potential wind slab avalanches) lower in the terrain than we are used to.

Problemi valanghivi

  • Wind Slabs

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

    The forecast is for 1.5 - 2 feet of new snow at treeline elevations.  Combine that with Strong winds from the SouthWest and we have a good recipe for Wind Slab avalanches.

    As we know here in Oregon, the wind can do a great job of picking up snow and blowing it onto lee slopes (transport).  It also breaks down the snow crystals as it moves them and can pack them into a consolidated slab that we call a Wind Slab.  When those slabs overlay some type of weak layer we have Wind Slab avalanches.  These avalanches typically occur at treeline and in alpine elevations where the wind plays the greatest role.

    These avalanches exist most often below ridgelines  and along features that act as wind breaks.  With Strong and Extreme wind speeds these loading patterns can be a bit less predictable and sometimes we find wind packed snow lower in the terrain.

  • Storm Slabs

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

    Gradually cooling temperatures overnight and during Tuesday should limit the potential for Storm Slab avalanches.  Nonetheless Storm Slabs should be on everyone's radar with such heavy rates of snowfall in the forecast.  The potential for dangerous storm slabs will increase as the snow piles up.  At nearly all relevent elevations this new snow will overlay very wet snow from recent rainfall, which may briefly contribute to instability in steep terrain.

    Test slopes are really the best tool to evaluate the storm slab problem.  If you see cracking on test slopes or other signs of consolidation in the new snow, steer clear of unsupported, steep terrain particularly in conjunction with terrain traps.

Avalanche Discussion

Several days with rainfall have put a bit of a damper on some folks riding over the holiday, and taken a bit of a toll on our snowpack as well.  It is looking promising that the current atmospheric river could be cold enough by Tuesday to deliver some significant snowfall.  Tuesday's avalanche problems will be the Wind Slabs and Storm Slabs we associate with major winter storms.  New snow will overlay some very wet snow from recent rain.  The Dec. 08 buried surface hoar is still evident in the snow pack (down 25-50 cm.) but is predominently unreactive.

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