Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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In sintesi

Friday will be a transition day as snow returns to the mountains, blanketing our soaked upper snowpack. You'll need to manage typical storm day dry avalanche problems while avoiding terrain where catastrophic wet slides could occur. New snow will be deeper and more sensitive to triggers in wind-loaded terrain or on the volcanoes.

Problemi valanghivi

  • Wind Slabs

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

    You'll need to put dry snow problems back on your radar if you venture into the mountains on Friday. Expect the largest potential slabs to be located in wind-loaded areas, such as leeward ridgelines, the sides of gullies/chutes, or the base of cliffs. You can look for texturing of the surface or new pillow-like drifts to help identify wind-loaded features that you should avoid. Using uptrack tests or small test slopes can help you determine how the new snow is bonding to the old surface. In most locations, we anticipate a fair to good bond to occur. The general cooling trend means storm snow should come in right-side up, but quick hand pits can help identify midstorm instabilities that you may need to manage. 

    On the volcanoes, more snow is expected. Anywhere you find 8-10 inches of new snow, start thinking about avalanches outside of wind-affected terrain.

    (2/7/2025)

    A shallow wind slab just below a ridgeline from earlier this season.

    The textured surface and relative stiffness are easy ways to identify wind-loaded features.

    Photo: Josh Lipkowitz

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Under the new white blanket of snow will be the sleeping dragon. Our snowpack is saturated from this week's atmospheric river and unseasonably warm temperatures. We haven't had a good overnight freeze in almost a week. Wet avalanches are impossible to predict and can often occur long after the rain has stopped. Although cooling generally helps resolve these issues, the initial cool-down can sometimes trigger a final round of slab or glide activity. Glide cracks and precariously hanging cornices may get hidden beneath new snow, making them harder to assess. Your best mitigation tool will be to avoid large avalanche slopes where one of these low-likelihood, high-consequence slides could occur. If a wet avalanche releases, it will be without warning and will likely be unsurvivable. This advice applies to all types of wet problems, including cornice collapses, slabs, wet loose, and glide avalanches.

    (3/27/2025)

    A very large wet slab that released naturally at Crystal Mountain on the evening of 3/26. 

    Photo: Crystal Mountain Pro Patrol

Avalanche Discussion

The good news is that we're on a general cooling trend, and snow is back in the forecast. That should help us start to put wet avalanche problems behind us and move forward as we wrap up March.  The bad news is that we may not be done with those wet problems quite yet. On Wednesday evening, a very large natural wet slab occurred at Crystal Mountain. This was only hours after the Crystal Mountain Patrol triggered a very large slab with explosives. Both of these avalanches failed on E-NE aspects around 6800'. On Wednesday, NWAC forecasts spotted several very large slides that had failed naturally during or shortly after the atmospheric river event. Many of these had a similar aspect and elevation. Is this a pattern or just the ones we are aware of? Either way, you should be mindful that these problems haven't been fully resolved despite mountain temperatures dropping 20+ degrees Fahrenheit over a 24-hour period. 

As you might expect, the upper snowpack is generally wet and weak due to the significant amount of liquid water. That will slowly start to change as we cool down, the surface freezes, and new snow stacks on top. In the coming days, we'll likely refer to this newly formed crust as our new ground and discuss dry snow problems above it. Until that happens, you could find sloppy travel and a mountain landscape covered in recent avalanche debris. Below the rain/snow line, the intake of water into our snowpack is expected to continue on Friday, and the likelihood of wet slides and soggy travel may be higher. 

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