Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

A winter storm with strong winds and mountain snow will create new avalanches concerns for many areas in the West South zone. Go around steep slopes where you notice the wind drifted snow into deeper and/or firmer slabs. As the storm breaks, periods of sunshine may cause the snow surface to quickly change, become wet, and produce small natural loose avalanches.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Strong winds associated with this storm may form slabs on exposed features at any elevation. Look for clues that the winds loaded snow onto a slope. When you see sharp cornices, drifts behind objects, and/or a textured surface, anticipate wind slabs nearby. Instead, find less-wind affected or lower angled slopes to travel. In many cases, these new slabs will form over a firm and smooth interface. This may allow them to trigger easily and run quickly. 

    Even in sheltered areas, you may still find some unstable snow. With cooling temperatures and modest anticipated snow totals, you’re most likely to encounter loose dry avalanches. These sluffs could run quickly over the firm curst. However, in locations that receive more than 8” of snow, take time to use small slopes to test the bond between the new snow and the old surface. Small slope tests and handouts can provide you lots of information to help you identify if soft slabs formed within the new snow. If your observations suggest a slab, steer around slopes greater than 35 degrees. 

    (3/20/2021) Example: Using visual clues is a great way to help identify the potential for Wind Slabs.

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    Some uncertainty exists about the potential for clearing Thursday afternoon. If the sun comes out, you may see the snow surface change rapidly. Watch for snow shedding from trees and new rollerballs falling down slopes to alert you to the impending loose wet issue. Steer around similar slopes and seek out more shaded aspects. While these slides should remain small, they can still harm you if they push you over a cliff or into a gully. At upper elevations, cooler temperatures and a very wind-affected snow surface should help limit the potential for loose wet avalanches.

    (3/12/2021) Rollerballs like this are a great sign that the snow surface has become wet and unstable. Photo: Robin Pendry

Avalanche Discussion

Snow totals could vary greatly across the West South zone by Thursday morning. Locations that accumulate more than 8” of snow could see locally more dangerous avalanche conditions. This is most likely to occur near Paradise, Mt St Helens, and Mt Adams. Take time to measure the new snow and adapt your plans if you find more than forecasted. In other areas, lower expected snow totals will limit the size of any potential avalanche. In all instances, you should encounter the most reactive slabs in the morning during or immediately following the storm. As the day progresses, prepare for a shift in avalanche problems from the new snow to wet snow. Make sure to plan your day with these dynamic conditions in mind. 

The storm snow will accumulate over a new interface (4/7). On most slopes, this layer is a firm melt-freeze crust. The snow may struggle to bond to this strong surface. At higher elevation northerly terrain, soft snow including weak facets and occasional surface hoar were reported this week. You may find that avalanches fail easily at this interface on any aspect and run quickly over the firm old surface. 

Even as temperatures cool, cornices and glide avalanches remain prominent in our minds. Pay attention to the slopes above your head. Don’t linger below large cornies and crevasse-like glide cracks. These features can fail without warning even during this more winterlike weather. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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