Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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In sintesi

Buried weak snow should keep you off large open slopes where unpredictable avalanches are more likely. Focus on these deeper layers of concern when making your travel plans. You may also need to manage recently fallen snow on slopes over 35 degrees where smaller avalanches are possible.

Problemi valanghivi

  • Persistent Slabs

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

    Buried weak layers exist throughout the zone and should be your primary consideration when making travel plans on Sunday. These layers are 2-3 feet below the surface and have produced whumpfing collapses as recently as Friday. Their distribution may be a bit spotty, but shaded slopes at mid and upper elevations are generally suspect. Avoid large open slopes in these areas, electing to travel in small, low-angled, or treed terrain instead. You may not get much feedback from these layers, warning you that a slope is ready to slide. Conditions may "feel safe" as you travel in the beautiful new snow, with no whumpfs, shooting cracks, or collapses. Don't be lulled into a false sense of security. The weak snowpack is lurking, and the only way to manage this problem is through avoidance.

  • Wind Slabs

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

    As snow continues to trickle in daily, new snow problems should be on your radar on slopes over 35 degrees. Wind-loaded slopes should be the most likely location to trigger an avalanche large enough to call consequential. Look for stiffer-feeling snow near ridgelines, the base of cliffs, convexities, or the sides of gullies/chutes. Use visual clues to help identify wind-loaded features to avoid, such as actively blowing snow, textured surfaces, fresh cornices, or drifts behind objects. 

    In sheltered terrain, you may see loose avalanches running in the surface snow. Some of them may be solar-induced during sun-breaks. Most of these should be small enough to call inconsequential but don't get caught off guard near a terrain trap.

    (2/8/2025)

    A shallow slab on a convex feature in the new snow. You may need to manage shallow slabs and loose avalanches in the upper snowpack on Sunday.

    Photo: Bryce Bartl-Geller

Avalanche Discussion

It was a sneaky avalanche day at The Pass on Saturday as the roughly 3-5 inches of new snow struggled to bond to the underlying surface. A subtle melt-freeze crust under the new snow appeared to have been a good sliding surface at mid and upper elevations. Slabs were reported on Mount Snoqualmie, Wright Mountain, Avalanche Mountain, and Bryant Peak. All of them were small, but they help highlight that even as we tip-toe around worrying about the big slides deeper in the snowpack, we still need to manage new snow problems. A little more wind Saturday night and another inch or two could result in similar conditions on Sunday. 

Over the past week, we have had a handful of bulls-eye information alerting us that the snowpack is unhappy. Whumpfing collapses and persistent avalanches have been reported as recently as Wednesday. The January Drought Layer (JDL) and 1/10 complex are the buried weak layers causing all the commotion. As alluded to in the persistent slab problem above, their distribution is a little spotty, and they may look different from slope to slope. But generally speaking, they're 2-3 feet below the surface and consist of multiple melt-freeze crusts and facets (weak snow). Since they got buried last weekend, we have watched these layers, and there hasn't been much change. You know, they've persisted. So, in response, not much has changed in the avalanche forecast or how you should manage them.  Keep your terrain selection simple and try to fight the lure of new snow on slopes you know are potentially dangerous. Test results continue to suggest that these layers can propagate a fracture given the right trigger, including propagation saw tests repeatedly failing with cut lengths around 35 cm [PST35 END].

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