Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

March sunshine could help increase loose avalanche potential on Wednesday. Keep an eye on the snow surface to see how it changes throughout the day, and head for shaded slopes if you see natural activity. The likelihood of triggering an avalanche on weak layers deep in the snowpack has decreased, but if you do, it will likely be unsurvivable. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3

    Weak layers that formed in early February have produced multiple very large avalanches in our zone over the past week. Persistent weak layers don't heal quickly and will be with us for some time. You'll need to exercise patience by avoiding large open slopes where these unpredictable slides could fail. They can be erratic, and it is hard to forecast what it may take to trigger one. On Tuesday, a skier triggered a 3 foot deep avalanche up at Stevens Pass, which was suspected to be on these same layers. Your best management tool will be to avoid large open slopes and their runouts where one of these wide, deep, and deadly avalanches could occur.

    (3/5/2024)

    A screenshot of the Mount St. Helens webcam. You can see a widely breaking avalanche on the shaded slope on the right. It likely occurred around 2/29.

    Photo: Andy Harrington

  • Loose Wet

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

    With another sunny day on the docket and slightly warmer temperatures forecast, we're throwing loose avalanches in as an official problem. Solar input could assist in the development of loose slides ranging in moisture content from dry to wet. Snow shedding from trees and rocks could trigger avalanches on the slopes below. If the March sun can overcome the cool ambient air temperature, expect avalanches to start to tip toward wet. Lower elevations and slopes that see direct sunshine have a higher chance of producing slides. These same slopes have the highest chance of snow "slabbing up" due to solar input. 

    Regardless of their moisture content, loose avalanches will start at a point and fan out as they move downhill. They are capable of growing large or triggering slabs as they descend. If you're on a sunny slope and see signs of natural avalanche activity, head for shadier aspects where this problem is less likely. 

    (3/4/2024)

    Small loose avalanches resulted after snow shed from trees in the March sunshine.

    Photo: Andy Harrington

Avalanche Discussion

Welcome to scary moderate avalanche danger. Although the likelihood of triggering a persistent slab is suspected to have decreased, the consequences and size remain the same. If you find the "sweet spot" on a slope or are in the wrong place at the wrong time, these avalanches will likely be unsurvivable. 

Tuesday was a beautiful and relatively quiet day in the West South zone. Crystal Mountain and White Pass Patrols reported minimal avalanche activity due to the March sunshine. However, the snow surface did warm, so expect a sun crust to develop by Wednesday morning on slopes that see direct sunshine. Shaded slopes continue to hold cold, dry snow, and you may still encounter lingering storm instabilities, such as wind slabs, on Wednesday. 

We have minimal recent information from the volcanoes. We were able to spot a large crown on the Mount St. Helens webcam, which likely occurred during the height of last week's storm. In the neighboring Mt. Hood zone, multiple very large avalanches have occurred this week due to wind loading. If you're traveling to Mount St. Helens or Mt. Adams, read the Hood forecast to get a feel for conditions and submit an observation. Expect to encounter several feet of storm snow from this past week, plenty of wind effect, and a poor snowpack setup buried 5-6 feet deep.

Weather station data indicates that the snowpack has been settling 3-5 inches every 24 hours around the zone. However, the potential for deep snow immersion (SIS) still exists. A SIS fatality occurred on Friday further north. Keep your partners in sight at all times, and be sure they don't tip into a tree well or get stuck in a spot they can't climb out of. 

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