Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A weak snowpack structure, continued snowfall, and fluctuating freezing levels will maintain dangerous avalanche conditions at Snoqualmie Pass. Slabs could fail easily or break more widely than you're used to. Keep your terrain selection simple by avoiding slopes over 35 degrees where triggering avalanches in new or old snow is more likely. 

Problemi valanghivi

  • Storm Slabs

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

    The snow is expected to keep falling at Snoqualmie Pass, increasing the potential size of slabs. On Sunday, most reported avalanches were small, but they could start creeping into the large category by Monday morning. Whether it's your classic storm slab due to a warming trend making the snow upside down, a poor bond with the underlying surface, or maybe a wind slab, it doesn't really matter. You will want to steer around slopes over 35 degrees and convexities where triggering a slide is more likely. You can use small test slopes or quick handpits as you travel to look for potential points of failure and help understand how the snow reacts to your weight as a traveler. With various surfaces buried by this storm, you may find that the new snow has bonded differently from slope to slope. In some locations, avalanches could fail on weak snow, breaking more easily or widely than you're used to. You may even observe natural avalanches occur during or shortly after periods of heavy precipitation or wind. Slabs should be larger and possibly more reactive as you ascend in elevation or in wind-loaded terrain.

    (2/16/2025)

    A widely breaking natural avalanche observed while riding out of the Gold Creek Snopark. This may have failed on buried surface hoar at the 2/13 interface.

    Photo: Josh Lipkowitz

  • Persistent Slabs

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

    Uncertainty is the central theme when discussing our persistent weak layers. They have been dormant for over a week, but snowpack tests and observations indicate they haven't healed much. This storm should provide a good test for the January Drought Layer (JDL) and 1/10 complex. Those are the facts. The uncertainty surrounds when (or if) the scales will tip and avalanches will start occurring on these layers. If you've written these layers off recently, you should again consider them when making trip plans, at least until the storm ends. The added load from the storm may stress them, but it could be another avalanche or you finding the sweet spot that tips them over the edge. The snowpack likely won't warn you before this avalanche strikes, making it hard to pinpoint where or when it could happen. Stick with the travel advice from the storm slab problem by avoiding slopes over 35 degrees, and you should also be able to manage this hazard throughout the storm cycle. 

  • Loose Wet

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

    Monday is supposed to be a touch warmer than Sunday, and the east flow may get scoured out. So that means there's a higher likelihood of a switch over to rain at lower elevations and in the western half of the zone. If you notice rain falling on dry snow, you may see rollerballs, pinwheels, or new fan-shaped avalanche debris soon afterward. Then you'll know it's time to head for lower-angled slopes, keeping aware of the terrain above you. 

    (1/10/2025)

    Wet avalanches originating in steep rocky terrain after a rain-on-snow event earlier this winter.

    Photo: Andy Harrington

Avalanche Discussion

Our first Cascadian storm in a while resulted in a somewhat touchy day at Snoqualmie Pass on Sunday. Numerous human-triggered and natural avalanches were reported from the Alpental Valley, Commonwealth Basin, and Gold Creek Snopark areas. Most reported avalanches were small, in the D1-D1.5 range, and failed within or at the base of the new snow (2/13 interface). An NWAC forecaster in the eastern part of the zone observed a widely breaking natural avalanche, believed to have failed on buried surface hoar at the base of the storm snow. On Saturday, NWAC forecasters observed buried surface hoar at the 2/13 in the Alpental Valley, and backcountry travelers observed rimed precipitation particles from the storm's onset. Although distribution is likely spotty, both could act as weak layers for storm slabs to fail easily or break widely throughout this storm cycle. In other locations, a melt-freeze crust at the 2/13 makes for a good bedsurface for slabs to run on. Small avalanches from Sunday may be large by Monday due to continued snowfall and a touch of wind. 

No activity was reported on our persistent weak layers on Sunday. However, NWAC forecasters on Microwave Hill and Cave Ridge noted that the JDL and 1/10 complex remained essentially unchanged, with propagation saw test results failing 40/100 END. Based on recent test results and observations, the focus is slowly shifting from the JDL to the 1/10 complex. On Saturday, a skier was caught, carried, and partially buried in an avalanche in Thunder Basin while traveling uphill. The picture of the avalanche appears to be a wind slab that likely formed during this week's ferocious east wind event. That said, the location certainly matches the type of terrain where we'd suspect the persistent slab problem could rear its ugly head. 

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