Bollettino valanghe

West Slopes South

Northwest 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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In sintesi

Sunshine and warm temperatures will bring a big change to the West South zone on Wednesday. Expect the mountains to respond by shedding snow from rocks/trees, triggering lots of rollerballs, and producing a few small avalanches. Don’t let one of these slides push you into a creek or over a cliff.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    While Wednesday won’t be the first sunshine the cold snow has seen, this time the sun will team up with significantly warming temperatures and light winds to help the snow surface to become wet and unstable. Once the weak surface crust breaks down, you’ll likely see plenty of new rollerballs and several small loose wet avalanches. Even though we expect most of these slides to stay small, a few could grow large enough to catch and carry an unwary traveler. Once you start noticing the snow shedding from trees and rocks, it’s time to pay attention to the terrain above you. Don’t let one of these wet slides push you into a creek or over a cliff. 

    Along with this warm-up, you could see cornices fail naturally. Fortunately, they aren’t generally as big and widespread as we see in most seasons. Even still, you don’t want to be under one of these looming waves of snow if it falls down. So, limit the time you spend underneath overhanging cornices.

  • Wind Slabs

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

    While most of these wind slabs are now a few days old and getting harder to trigger, we keep getting just enough reports of wind-affected snow and human-triggered slides to keep them on our minds. You’re most likely to encounter one of these potential avalanches on a steep unsupported slope or convex rollover. So, before you commit to higher consequence terrain, look for clues like sharp drifts, textured surfaces, and fresh cornices to help you anticipate wind-loaded areas. In some isolated locations, these slabs could be large enough to bury you. Steer around smooth pillow-like slabs, especially where slides could push you off a cliff or bury you deeply in a gully.

    (1/16/2023)

    Example: A human triggered winds slab on a convex rollover near ridgecrest. [NW 6400']

    Photo: Public Observation

Avalanche Discussion

While not the craziest warm-up we’ve seen in the West South zone, Wednesday's sunshine and rising temperatures will certainly be a shock to the snowpack. Fortunately, brief sunny periods over the past few days and a weak surface crust should help take the bite out of the swing in the weather. This will help limit the size and distribution of most slides. However, warm-ups are tricky and there’s always some uncertainty about how the snowpack will respond. If you see avalanches gouging into older snow or growing larger, the scales have tipped, and its time to step back and let the mountains shed some snow. Slides could involve snow as deep as the MLK crust if they grow large and more powerful. 

Recent windy days really reshaped the snowpack in many areas. This resulted in scoured slopes, wind-packed snow, and deeper slabs. However away from wind-affected areas, you’ll typically find 1.5-2 ft of snow (45-60cm) over the very stout and prominent MLK crust. While subtle interfaces (1/21, 1/18 ) exist between each storm (or sun crusts on southerly aspects), we haven’t seen any recent avalanches on these older layers.

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