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
1 · Debole
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The weak snowpack poses the risk of a low likelihood but high consequence avalanche. You can minimize your exposure to this hazard by avoiding steep and sustained open slopes on west, north, and east aspects. You’ll find safer travel and great snow in lower-angle terrain and in the forest.

Problemi valanghivi

  • Persistent Slabs

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

    Weak layers of sugary snow, often interspersed with crusts, lurk beneath 1.5-3.5ft thick slab. This poor structure is well documented and has produced multiple avalanches, audible collapses, and poor test scores, all of which suggest that a dangerous avalanche could ensue if you find the “sweet spot”. The likelihood of triggering a slide on these layers is low, but low probabilities don’t matter to the person who draws the short straw. Avoidance continues to be the only surefire way to stay safe. 

    If you decide to roll the dice, stack the odds in your favor. Before committing to a slope, discuss the consequences of a slide on the terrain you are considering. Hedge towards simpler, smaller, and lower-angle. Choose planar and supported terrain with clean runouts and no terrain traps, only expose one person at a time, and minimize your exposure on the ascent. Keep in mind that areas where the slab is thinner, such as around rocks, trees, and locally wind-scoured spots may act as trigger points. Be wary of these specific features within wind-loaded start zones below ridgelines and cliff faces. Complex terrain often holds this dangerous combination of thicker and stiffer slabs with locally thin areas on the slope.

    A few other factors for Wednesday. The sun should be out and it will be the warmest day in quite a while in western parts of the zone like St. Helens and Rainier. Look for small loose avalanches shedding from steep slopes and rocky faces in the sun. In addition, winds are forecast to increase in the afternoon. Avoid lee start zones if you see actively blowing snow.

     

    (2/1/2025)

    This intentionally triggered persistent slab in the West South zone propagated the entire width of the feature. It failed on facets over a thin crust. ENE, 6200ft, SS-ASc-D2-R3-O, 20-24 in deep, 200 ft wide.

    Photo: Dallas Glass

Avalanche Discussion

NWAC forecasters and avalanche professionals out on Tuesday noted thin wind slabs below ridgeline, scattered dry loose avalanches on slopes facing the sun, and generally excellent snow. Tuesday’s sun may have formed a thin crust on south-facing slopes moving forward. Another low-cut length propagation saw test in the Crystal backcountry shows that while it may be unlikely to initiate a fracture in the weak layer, if you do it could propagate and release a dangerous avalanche. Observers also noted widespread surface hoar and near-surface faceting on slopes sheltered from the wind with a clear view to sky.

As for the persistent slab, the structure really isn’t changing. The 1/10 complex and the January Drought Layer are still weak, but as we get further out from the last loading event it is becoming harder to trigger an avalanche on these layers. Not impossible, just unlikely. That may very well change with a fresh round of wind and snow late this week through the weekend. In the meantime, stay humble and respect the inherent uncertainty associated with these types of avalanches. There is lots of great and safe snow out there in mellow terrain!

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