Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

If you've got a date with the mountains on Friday, bundle up and avoid wind-loaded slopes. Vigorous east winds have created unstable slabs in unusual locations and added load over buried weak layers. Visual clues and red flags such as shooting cracks, whumpfing collapses, and actively blowing snow can help you identify dangerous slopes. 

Problemi valanghivi

  • Wind Slabs

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

    Strong easterly winds should eventually give way to moderate westerlies by the end of the day on Friday. Slabs formed over this windy period might overlay soft snow from earlier this week, making them more reactive than you're used to. Or they could sit on a melt-freeze crust on sun-exposed slopes, giving them a good sliding surface. With easterly winds, slabs form on different aspects than usual and sometimes further down in the terrain as slopes get cross-loaded. Visual clues such as actively blowing snow, textured surfaces, and fresh cornices can help you identify wind-loaded aspects. Even if slabs exist in some unusual locations, the type of terrain where they form will remain essentially the same. Look for them on the leeward side of ridgelines, convex slopes, the base of rocks/cliffs, or the sides of gullies/chutes.  Zoning in on pillow-like drifts, areas that look "fat," or stiff, hollow-feeling snow can help you identify slopes to avoid. 

  • Persistent Slabs

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

    As we add load to the snowpack through snow showers and wind events, the slab over our persistent weak layers should thicken. The question is how much load until these layers wake up and produce avalanches. Our hunch is we'll need a little more than what you'll find on Friday, but don't take that to the bank. Your best game plan is still avoidance of large open slopes, especially if they're wind-loaded.  Discuss the consequences of a slide with your loved ones if you are considering non-wind-loaded steeps on the shaded half of the compass. Your default should be to choose simpler, smaller, and lower-angle terrain. 

    (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

The easterly winds were cranking in the West South zone on Thursday. NWAC forecasters in the Crystal area observed plenty of blowing snow, shooting cracks, and natural activity. Backcountry travelers across the valley had a similar report. Rangers at Mount Rainier observed blowing snow and sensitive wind slabs forming. And the White Pass ski area stayed closed for the day due to the ferocity of the wind. Wind speeds were gusting into the 60 mph range at NWAC weather stations, making for a brutally cold day.

As we look ahead to Valentine's Day, the easterlies should begin to calm down, but the wind slabs formed during this event will still be fresh for human triggers. They'll likely still be touchy on Friday morning before our weather pattern slowly changes toward westerly winds and moderating temperatures. If the westerlies come in early, you may even see a fresh batch of wind slabs start to form by day's end. 

Wind-loaded slopes will be the more in-your-face problem, but our persistent weak layers are still down there. They're a few feet below the surface and have been dormant for the better half of a week now. That doesn't mean this problem is over with. As we incrementally load these layers through snow showers and wind over the weekend, keep an eye on how this problem changes. We may be bumping the likelihood to possible. Obviously, if you experience whumpfing collapses or see widely breaking avalanches, dial your terrain selection way back, and please let us know about it.

Regioni coperte