Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

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

Update: Decreased avalanche danger and likelihood of storm slabs due to expected lower precipitation amounts. 

The first in a series of winter storms will dramatically increase the avalanche danger Sunday, especially near the volcanoes. You may trigger a shallow avalanche on any steep open slope where you find more than 6” of storm snow. In some locations, avalanches could fail on weak older layers in the upper snowpack, allowing them to grow larger than storm totals indicate.

This storm is much bigger for locations near Mt St Helens and Mt Adams. In these areas, you may encounter dangerous avalanche conditions and stormy weather.

Avalanche problems

  • Storm Slabs

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

    This storm will impact all our major access points within the West South zone very differently and result in a wide array of avalanche conditions. On top of that, weak layers in the upper snowpack vary by aspect, elevation, and location. You’ll need to test the snow frequently to see how conditions change as you travel. Hand pits, uptrack tests, and small slopes can help you see how the new snow reacts. You may need to use your shovel to dig a bit deeper and check for the presence of weak facets just above the very stout and prominent Early March Crust. When you find the snow fails suddenly in any of your observations, you've found the storm slab problem. Steer around steep slopes, especially above terrain traps where even shallow avalanches could hurt you. For most locations, we think that the tipping point will be around 6” of new snow.

    At lower elevations and in locations that receive less precipitation, we expect the new snow will bond well to the surface crust. Any avalanches you trigger should be small and shallow.

    (3/12/2022) Hand pits and hand shears can help you check for strong over weak snow in the upper snowpack, Photo: Dallas Glass

Avalanche Discussion

It’s hard to say exactly how this storm will play out around the West South zone Sunday. The bulk of the precipitation seems to stay south of Hwy 12. This makes us very concerned about locations near Mt St Helens and Mt Adams. In these locations, significant snowfall and extreme winds could combine to cause a natural avalanche cycle and produce very dangerous avalanche conditions. For places like Mt Rainier, Crystal, and White Pass, if the storm shifts just a bit north, more snow could fall than expected.

To add to the complexity, we’ve been tracking weak snow in the upper snowpack for the past several days. Sugary facets were observed in the Crystal and Paradise backcountry areas just above the very prominent Early March Crust. We suspect a similar snowpack may exist in other locations. Well developed facets (1-2mm) were seen primarily on NE-NW aspects. However, an NWAC forecaster and NPS ranger at Paradise Saturday found these weak grains on all aspects near treeline. Warm and sunny weather Thursday-Saturday allowed the snow surface to become wet and sticky in many places. This likely introduced a new crust (3/12) into the upper snowpack. This curst is likely much thicker on sunny slopes and more breakable on shady aspects.

As we enter this stormy period, avalanches could fail on these older weak layers and allow slides to grow larger. Each location may reach its breaking point at different times and cause this to be very tricky to forecast. Fortunately, we do not have any layers of concern below this very stout and easy to identify Early March Crust.

Regions covered