Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

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

New snow measured in feet has resulted in dangerous avalanche conditions in the West South zone. Expect to find overlapping avalanche problems and less obvious signs of instability than you’re used to. Avalanche potential may vary significantly from slope to slope, so carefully evaluate each piece of terrain individually.

Avalanche problems

  • Storm Slabs

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

    Monday’s storm totals varied across the zone, but everywhere you go, it will be deep. As a result, you will need to manage various new snow problems on Tuesday. Storm slab, wind slab, and dry loose will all be in play. Since it’s so deep in many areas, our usual tips to gauge reactivity, such as using uptrack tests or small test slopes, may not work well. The best option will be to dig down to the 2/24 interface with your hand or shovel, looking for heavy snow over weaker snow or easy and clean failures. Potential slabs will be larger as you ascend in elevation or in wind-loaded terrain. You could trigger loose avalanches on steep slopes in areas with unconsolidated snow. Evaluate each slope carefully for instability and avoid terrain over 35 degrees.

    (2/26/2024)

    An explosive triggered slab that broke up to 2 feet deep at Crystal Mountain. It failed down to the Early February Crust. 

    Photo: Crystal Mountain Pro Patrol

Avalanche Discussion

The West South picked up anywhere from 1-2 feet of snow during this past storm, creating the 2/24 interface. Avalanche professionals in the Crystal Mountain backcountry reported that the storm snow was fairly right-side up but was able to get failures at the 2/24 interface with tilt tests. The Crystal Mountain and White Pass Pro Patrols both reported triggering loose and slab avalanches up to size D2. No on-the-ground observations were received from the volcanoes. However, the USGS reported picking up numerous very large avalanches with their seismic equipment on Mount St. Helens and Mount Rainier. 

Before this storm, an assortment of surfaces existed. Facets, surface hoar, firm crusts, and wind slabs had spotty distribution, leading to an unpredictable 2/24 interface from slope to slope. Deeper in the snowpack, a series of small storms, clear weather, and strong wind events since our last atmospheric river has created irregular potential weak layers (2/24, 2/19, 2/14) above the stout Early February Crust (EFC). The distribution and extent of any of these layers has been challenging to pin down. Most of these interfaces are associated with facets, buried surface hoar, or crusts. Some may have produced avalanches that stepped down to the EFC in recent weeks.

In the storm slab description, we mentioned various new snow problems. We didn’t mention the possibility of slabs breaking on persistent grain types at any of these interfaces. The spotty distribution and lack of widespread avalanche activity have made it challenging to have confidence in calling out a persistent slab problem. But as the week rolls on and we continue to load these layers, don’t be surprised to see a few avalanches break widely or deeply in isolated locations. The observations from the USGS on Monday may be the tip of the iceberg and an indication of things to come. 

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