Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

In sintesi

Expect very dangerous avalanche conditions to develop and peak during the height of the storm Wednesday. Several overlapping factors will make this anything but a normal powder day. Put plenty of space between you and places where avalanches start, run, and stop.

Problemi valanghivi

  • Storm Slabs

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

    High snowfall rates and slightly warmer temperatures should easily create slabs in the new snow. Expect natural avalanches, particularly during periods of heavier precipitation. These slides could include most or all of the new snow. By the end of the day, that could be avalanches 1-2ft thick! In more wind-exposed areas and at higher elevations, expect slabs to be firmer and deeper. 

    This new snow will fall on a patchwork of surfaces, including some weak facets and surface hoar. The variability may help keep slabs from propagating widely at the newest interface. However, given the variable conditions, it will make predicting how any individual slope will react nearly impossible. Some features could trigger remotely, while others nearby seem stable. 

    With so many factors at play, every steep open slope is suspect regardless of its aspect or elevation.

    (1/6/2024)

    Example: Even small openings in the forest could produce slab avalanches. 

    Photo: Andy Harrington

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    We don’t exactly know how the deeper layers will react to the new snow load. However, it feels like a safe bet that it won’t help matters. Given the near-constant influx of observed very large crowns over the past 10 days, the presence of this issue isn’t in question. We have reported slides from every region and on nearly every aspect.

    These layers are so deep, that they won’t “talk to you” and show signs of instability unless you dig. It will likely take a bigger trigger such as a storm slab or cornice to step down to these older layers. If they do, avalanches could wrap around terrain features, involve massive amounts of snow, and be unsurvivable. Best to simply give them some distance and stay away from larger avalanche paths. 

    (1/16/2024)

    Here you can see just a sampling of the recent persistent slab avalanches in the West South zone over the past 10 days. 

    (The number is recorded avalanches in our database, and does not include all avalanches in the zone)

    Photo: Dallas Glass

Avalanche Discussion

Buckle up! We’re starting another long stormy period in the West South zone. The combination weak surfaces, buried persistent layers, and additional snowfall could make the next few days unique. Don’t run the same ole-playbook.

If you’re out on Wednesday morning, conditions might not be that dangerous. However, as the storm intensifies, what felt very benign could suddenly become scary. By the end of the day, most locations will have 1-2.5ft of new snow. 

Sure, the volcanoes will get more snow, but they will also see additional warming. That could result in some wet avalanches at lower elevations. With snow well below our forecast area, this could mean avalanches on open slopes down in the deep, dark forest. 

There’s a lot going on in the snowpack, but there are three layers to really watch going into this storm. 1). The 1/16 interface could hold facets/surface hoar. 2). 1/8 the base of last week's storm snow was generally strong. 3). The Solstice crust/facet matrix down about 3-5ft is suspected in all of the recent very large slides. This persistent layer has only gotten weaker and the structure is present nearly everywhere. 

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