Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Windy weather Monday night into Tuesday could build a fresh set of slabs on the lee sides of ridges and exposed features. With all the new snow some of these avalanches may grow large and deadly. Avoid steep areas below cornices and where you see thicker pillow-like drifts.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    This problem is anything but certain. Increasing clouds should keep the effects of the sun at bay and minimize any loose wet avalanche issues. However, if you experience prolonged periods of sunshine, take note. Snow will shed from trees, rocks, and steep faces and likely trigger avalanches on these slopes below. 

    If you see new rollerballs or fan-shaped debris, avoid traveling on or under similar slopes. That means paying attention to the terrain above you and not lingering underneath any sunny rock faces.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    New wind slabs may form Monday night and could be fairly easy to trigger first thing Tuesday morning. Fortunately, plenty of clues should exist to help you figure out which slopes you want to avoid. Look for textured surfaces, drifts, and sharp cornices to point toward wind-loaded terrain. You’re most likely to encounter a wind slab near ridgecrest, in the tops of chutes, on convex rollovers, or along the base of cliffs. 

    Give any firm pillow-like drift a wide berth. With all the new snow, many of these avalanches could be large enough to bury you. Instead, seek out more sheltered, wind-scoured, or lower angled areas to avoid this problem.

    (2/24/2023) Wind clues like these can help you anticipate wind loaded aspects. Photo: Dallas Glass

Avalanche Discussion

The storm just ended and now the sun is trying to come out. These days are often rife with uncertainty. Observations from Monday were limited and we’re not quite sure how conditions are shaping up. Think about easing into the terrain by using smaller lower consequence slopes to see how the snow reacts before committing to larger lines. 

Not surprisingly snowfall totals varied around the West South zone. Mt St Helens was the clear winner with ~2-3 ft of snow. The remainder of the zone received a slightly more modest 8-18 in. This snow buried a new 3/12 interface. Surface hoar and facets were seen prior to the snowfall, but it’s unclear if these weak grains survived the warm, wet, windy weather. You can use small slopes and up-track tests to investigate this interface. If you see the snow cracking or failing in blocks, avoid nearby slopes greater than 35 degrees. 

The only avalanche observations from Monday came from the USGS, and boy are they doozies. Two very large avalanches (D3-D4) occurred on the east side of Mt St Helens Sunday night and early Monday morning. The largest of the two was likely a D4 slide that gouged into the snowpack and traveled from near the crater rim (E, 8000ft) down to much lower elevations. While these were the only two slides we heard about, poor visibility severely hampered avalanche observations. 

One other hazard on our brain is the looming cornices along ridgelines. These beasts may fall down naturally during warmer sunnier days. Don’t hang out near or underneath these overhanging blocks of snow.

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