Bollettino valanghe

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Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

You can trigger a widely propagating, dangerous avalanche on open slopes steeper than 30 degrees on a persistent weak layer. This is a scary moderate, where it’s tough to say exactly how widespread or reactive the problem is, but we suspect it exists on most open slopes. Terrain selection puts control of the problem in your hands - travel along ridgelines, through dense trees, or on smaller slopes where less consequence from an avalanche exists.

Problemi valanghivi

  • Persistent Slabs

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

    A layer of surface hoar buried 1 to 2 feet beneath the snow’s surface exists on sheltered slopes. It is present in areas where it was not destroyed by wind before being buried. You can read a couple observations from Saturday HERE and HERE. In some recent pits this layer was found to be very reactive, where columns failed on isolation. In other locations results weren’t as alarming. Natural and remotely triggered avalanches occurred on this layer about a week ago. There haven’t been large changes in snow conditions since these events. 

    Buried surface hoar maintains notoriety for producing avalanches that can release on a low-angle slope, break above you, propagate widely, or trigger remotely. Additional recent observations have led us to believe this problem exists in most areas where the surface hoar was not destroyed by sun or wind. This means most slopes aside from steep southerly slopes and areas where an abundance of vegetation is poking through. Assume the problem exists on smooth, open snow-covered slopes at this time. 

    Stick to ridges, thick trees, and slopes less than 30 degrees to maintain a margin of safety. Steer around steeper, unsupported, or actively wind-loading slopes. Whumphs and rumbling collapses provide a warning that the risk of triggering an avalanche on a steeper slope nearby very well could happen.

    (12/17/2022)

    An obvious layer of buried surface hoar, seen as a thin grey line in this pit wall, is the culprit right now. 

    Photo: Matt Lubar- Cascade Mountain Ascents

Avalanche Discussion

What we’re seeing in the backcountry right now is a scary moderate. It appears to be getting harder to trigger avalanches on this persistent layer, however, the buried weak layer still exists. It is now more difficult to trigger an avalanche due in part to surface layers being harder but if you do trigger an avalanche on this layer the avalanche will probably be larger and more dangerous than the avalanches which occurred a week ago. Take this into consideration before stepping out onto large, high-consequence slopes. 

Looking into the future, snow surfaces are coated with a new layer of surface hoar, something to pay attention to as an unsettled weather pattern heads our way.  If you make it out on Sunday, share what you saw with us by submitting an observation. The more information we have, the easier it is to produce an accurate forecast so that you can have a safer day in the backcountry. 

Regioni coperte