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

Sunshine is expected throughout much of the West South on Tuesday. This could alter the snow surface and the potential for avalanches in a number of ways. Keep it simple by avoiding large open slopes where deep and deadly avalanches are more likely and default to shaded aspects if you notice natural activity.

Avalanche problems

  • Persistent Slabs

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

    Weak layers that formed in early February have been waking up as the load over them increases. That trend could continue on Tuesday if sunshine helps consolidate low-density snow into a slab. In some areas, you could consider this a deep persistent problem. Elsewhere, these weak layers are shallow enough to label it as persistent. Regardless of its depth, this problem should be shaping your travel plans. 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. Just because a slope has tracks doesn't mean it's safe. All it takes is one person to find the "sweet spot" to trigger one of these beasts. 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.

    Natural and human-triggered slides have occurred on the Early February Crust (EFC) and other layers just above it near Crystal Mountain. Snowpack tests at White Pass and Paradise have resulted in sudden and clean breaks on these layers. In neighboring zones, avalanches on these interfaces have been triggered remotely and even resulted in a fatality on Friday in the nearby East South. 

    (3/4/2024)

    A very large avalanche spotted near Sourdough Gap in the Crystal Backcountry. This likely occurred during the height of the storm on 2/29.

    Photo: Andy Harrington

  • Wind Slabs

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

    You'll also need to continue to manage avalanche hazard based on the recent storm snow on Tuesday. The most likely location to trigger a slab will be in wind-loaded terrain. The base of cliffs, convex rollovers, and the tops/sides of narrow chutes are all common features where the wind likes to deposit snow. You may notice textured surfaces or large drifts indicating wind loading. Much like the persistent slab problem above, the introduction of March sunshine could increase the reactivity of these slabs on slopes that see direct sunshine. If you suspect that a slope is wind-loaded, choose a different path.

    Other storm snow related issues could exist on Tuesday. See the discussion for more details.

    (3/4/2024)

    A skier-triggered wind slab near the base of rocky terrain at White Pass.

    Photo: Susie Glass

Avalanche Discussion

Tuesday should be a break in the pattern that has delivered feet of snow to the West South over the past week. The sun is expected to come out as winds die down and precipitation tapers. The exception may be in the southern half of the zone, where snow showers and gusty winds could continue. If you're traveling on Mount St. Helens or Mt. Adams, you may want to take a look at the neighboring Mount Hood forecast. Numerous very large wind slab avalanches occurred there over the weekend, and the weather may more closely match.

On Monday, Crystal Mountain was in the sunshine with little wind. As snow shed from trees and rocks, a few small dry loose avalanches occurred on the slopes below. The sunshine afforded decent visibility, and very large avalanches were spotted near Sourdough Gap and in Mount Rainier National Park. They likely failed during the height of the storm last week. At White Pass, close to 10" of snow fell overnight, and backcountry travelers spotted a few small naturals and triggered a wind slab at the base of a rocky feature. After the sun came out, slopes near Highway 12 reportedly had loose avalanche debris piles. Looking at weather station data across the zone, settlement rates have accelerated, and on-the-ground observations confirm that the storm snow is generally right-side up and settling well. No new reports were received from the volcanoes or elsewhere.

On Tuesday, we're throwing the March sun into the mix. We did not officially list a wet problem because the assumption is that most avalanche activity aided by the sun won't be wet. We believe solar input will result in snow shedding from trees and rocks, possibly triggering loose avalanches on the slopes below - similar to Crystal on Monday. The snow could also "slab up" on slopes that receive direct sunshine. This occurred on a steep southerly aspect in the neighboring Snoqualmie Pass zone on Monday. We won't rule out the possibility of a "moist loose" avalanche or something approaching wet. In the end, the moisture content doesn't matter. If you're on a sunny slope and see signs of natural avalanche activity, head for shadier aspects. Once you get there, you may be able to trigger dry loose avalanches in the low-density snow, although the settlement rates and lack of a good bed surface should help keep them in check.

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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