Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Snowy and windy conditions should continue Sunday evening, leaving us more potential Wind Slabs to deal with on Monday. Actively blowing snow or newly formed cornices can help you identify wind-loaded features to avoid. Choose travel routes that give you plenty of options to avoid exposed areas prone to wind. 

Avalanche problems

  • Wind Slabs

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

    Gusty winds should continue to move snow into thicker and potentially unstable piles for you to avoid on Monday. Look for these slabs to develop near rocky features such as confined gullies or the base of cliffs. They may also be lurking on convex slopes or on the leeward side of ridgelines. You can look for actively blowing snow to help identify newly building slabs, or look for visual clues such as fresh cornices, textured surfaces, or small drifts behind natural objects to help you identify where the wind has been at work recently. If you notice smooth pillow-like piles or find yourself in a deep stiffer pocket of snow, you should avoid these areas.

    (12/17/2022)

    Blowing snow in the Tattoosh Range near Mt Rainier, Saturday 12/17

    Photo: Andy Harrington

Avalanche Discussion

It took a while for the snow to start to fall around the West South zone, but it certainly didn’t take as long for the winds to arrive. It was a breezy day, with the NWAC weather station at Muir recording gusts over 100 mph in the afternoon. Down at White Pass, we saw gusts as high as 85 mph. These winds were easily strong enough to move around already in-place low-density snow along with the newly fallen storm snow. The winds should continue to howl through the evening and into Monday morning. Storm totals are expected to be somewhat moderate compared to Pacific Northwest standards, but it could be hard to measure new accumulations with winds this strong. So you may have to make observations for yourself in the field to determine how much snow has piled up and where the wind has deposited it.

The recent storm snow is falling on a variety of previous surfaces (12/18 interface), some of which are weak. Sun crusts on more southerly slopes and surface hoar on more sun-sheltered slopes were found on or near the surface prior to the storm. Near surface facets were found on a variety of aspects. In some locations, the snow may struggle to bond to these surfaces or slide easily on the pre-existing sun crust, creating loose avalanches on Monday. We expect at some point in the next week we will reach a tipping point for more widespread slab avalanches as we incrementally load the 12/18. When that point is reached, the resulting slides may break in surprising ways by spanning far distances, wrapping around terrain features, or breaking above you. 

Deeper layers in the snowpack such as the 12/8 and 12/5 are still present but will be taking a back seat in our minds for the next few days until the load above them increases. While avalanches on these layers are not impossible, we believe them to be a low probability. 

Regions covered