Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Tuesday should be a bit of a transition day as temperatures drop and precipitation changes from rain to snow. You’ll likely need to manage both wet and dry avalanche problems until the snowpack has had more time to adapt to the recent load. Stay clear of open slopes over 35 degrees if you are sinking into a wet snow surface past your ankle.

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    It is going to take a bit of time for the snowpack to adjust to the amount of rain it just ingested. As a result, wet avalanche activity may diminish but will not be fully eliminated on Tuesday. As the storm cools and liquid precipitation tapers, don’t overlook the potential for unpredictable and dangerous avalanches on open slopes over 35 degrees. They’ll be possible anywhere you encounter a wet and punchy snow surface. 

    In most cases, your chances of initiating a Wet Slab avalanche are minimal. But a larger trigger such as a cornice collapse or other avalanche could do the trick. You may be more likely to set off a smaller slide, such as Wet Loose, that could trigger a slab as it descends. Any triggered wet avalanche has the potential to entrain significant snow and grow large. 

    (1/14/2023)

    Example: Wet avalanche debris as a result of a rain-on-snow event earlier this season.

    Photo: Ian Nicholson

  • Wind Slabs

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

    As temperatures continue to drop and snowfall returns to the West South, you could encounter some new snow problems. We anticipate any accumulation to have a favorable bond to the warm and wet surface. That said, be leery of features where the wind formed slightly deeper and firmer slabs. Textured surfaces, sharp cornices, or actively blowing snow can help you locate these wind-loaded pockets. Pay close attention near ridgelines or rocky terrain where you’re more likely to trigger one of these small avalanches.

    (3/17/2023)

    Signs of wind transport like this can help you identify where slabs may exist.

    Photo: Dallas Glass

Avalanche Discussion

As of Monday afternoon, weather stations around the West South zone have recorded anywhere from 1.3 - 2.3 inches of precipitation since Saturday afternoon. They predominantly measured rain that helped to soak and destabilize our wintertime snowpack up to around 7000 feet.

On Monday, Crystal Mountain Pro Patrol reported triggering multiple very large (D2.5-3) Wet Slab avalanches during their mitigation efforts. These slides reportedly involved most if not all of April’s snowfall and ran far distances. Away from the slabs, Wet Loose avalanches were easy to trigger and again, ran far distances entraining wet snow to increase their size and destructive potential. Similarly, scientists for the USGS on Mount St. Helens recorded up to 5 large to very large natural avalanches with their seismic equipment overnight Sunday into Monday. At White Pass, results were more modest, but Pro Patrol similarly found wet snow conditions ripe for triggering loose avalanches. They also observed natural activity in the terrain surrounding the ski area.

Rainfall should continue at low to mid-elevations into Monday night before freezing levels slowly lower and snow returns. If everything goes as planned, we should see snow replace liquid precipitation down to most trailhead locations on Tuesday. Unfortunately, it’s springtime and the weather doesn’t always go as planned, so don’t be surprised if you encounter wet precipitation - whether that be rain, snow, or some combination (snain). There’s a chance you could even see a few sun breaks in the afternoon.

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