Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

On Sunday, a typical Cascadian storm should result in dangerous avalanche conditions at Snoqualmie Pass. New snow problems will be front and center, but this storm will also test our buried weak layers. Keep your terrain selection simple by avoiding slopes over 35 degrees, where triggering an avalanche is more likely.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    As new snowfall stacks up, the potential for avalanches will increase on slopes over 35 degrees. Whether that'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 those steeper slopes and convexities where triggering a slide is more likely. You can use small test slopes or quick handpits as you travel to help understand how the snow is coming in and reacting to your weight as a traveler. With various surfaces currently in place, you may find that the storm snow has bonded differently from slope to slope. In some locations, weak buried surface hoar could result in avalanches breaking wider or easier than you're used to. You may even see a few natural avalanches occur during or shortly after periods of heavy precipitation or wind. Obviously, shooting cracks, whumpfing collapses, or recent avalanches are all red-flag signs that the snowpack is unhappy and you're flirting with danger. 

    (2/4/2025)

    A natural storm slab avalanche on Chair Peak from our last major storm cycle. 

    Photo: Dallas Glass

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Here's the avalanche problem that should worry you the most. Uncertainty abounds regarding persistent slabs, and this one is no different.  Our persistent weak layers have been dormant for over a week, but snowpack tests and observations indicate they haven't healed much. After getting buried earlier this month, there was a lot of talk that these layers lacked the slab over them to produce avalanches. Well, all that low-density snow has settled and compressed into a slab, and now this storm should provide an excellent test for the January Drought Layer (JDL) and 1/10 complex. We're not confident that this will be enough load to tip the scales, but this storm certainly warrants a bump in likelihood for this problem. If you've written these layers off, it's time to bring them back to the forefront. It may not even be the loading from the storm but another avalanche in new snow that steps down and creates a larger and potentially more dangerous slide. 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 problem throughout the storm cycle. 

    (2/2/2025)

    This avalanche released after a audible whumpf. The slide failed on facets over a crust and released the entire width of the feature. NE, 3700ft

    Photo: Summit at Snoqualmie Professional Patrol

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    It's just one of those seasons. We are rolling back to a regular Cascadian storm, so there's a threat of rain at Snoqualmie Pass. You'll know quickly enough if this avalanche problem develops because rain will fall on dry snow around you. You may see rollerballs, pinwheels, or new fan-shaped avalanche debris at that point. If so, you should head for lower-angled slopes, keeping aware of the terrain above you. With freezing levels in the 3500-4000' range, this problem should only affect the lower elevation trailheads or the west side of our zone. But if we lose the east flow or the storm is warmer than expected, this problem could expand higher into the mountains.

    (1/10/2025)

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

    Photo: Andy Harrington

Avalanche Discussion

Sunday is shaping up to be a somewhat complex but dangerous day in the mountains at Snoqualmie Pass. Typically, with a storm like this, we're dealing with new snow problems, such as storm and wind slabs, with the possibility of wet avalanches at lower elevations. That all still holds true for Sunday, but the lingering persistent weak layers throw a real wrench in things. It will be almost impossible to pinpoint the exact slopes where the persistent problem may exist or what it will take to trigger a slide. Any triggered avalanche, whether in new snow or old, will only increase the potential for stepping down and activating the deeper and more unpredictable JDL and 1/10 complex. A handful of human-triggered slides were reported on Saturday in wind-drifted terrain. On Sunday, you can make it easy on yourself by avoiding slopes over 35 degrees, where triggering a new snow avalanche and a persistent slab is more likely. 

On Saturday, NWAC forecasters in the Alpental Valley found variable surfaces, shallow wind slabs, and buried weak snow. Preserved surface hoar was found a few inches below the surface, likely buried on 2/13. This resulted in some easy failures in tests, but with only a few inches on top, it didn't produce much in the way of avalanches. The JDL and 1/10 looked essentially the same as they have for much of February.  Backcountry travelers on Roaring Ridge noted rimed precipitation particles from the storm's onset. Surface hoar and rimed particles are examples of weak snow that could result in a few avalanches breaking widely or connecting terrain features in isolated locations. Their distribution is notoriously spotty, so they may not come into play on Sunday, but keep them in the back of your mind, just in case.

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