Boletín de aludes

West Slopes South

Northwest Avalanche Center
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Peligro de aludes

Sun
Alta montaña
4 · Fuerte
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Dangerous avalanche conditions exist. You can easily trigger an avalanche within the new snow. Deadly and deep avalanches are still possible on weak layers near the mid-January rain crust. With complex and overlapping avalanche problems, keep your terrain choices simple, steer around steep open slopes especially when you see blowing snow or encounter fresh cornices.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    New snow overnight Friday will continue to build fresh and reactive wind slabs. Cold temps mean these slabs will be softer than we often see (but not less dangerous)--use the current wind direction and blowing snow as the best indicator of wind slab formation.  If you notice drifts or fresh cornices, steer around nearby steep slopes and seek out less wind-affected terrain.

    The recent cold and clear weather allowed weak snow to develop on some surfaces. If new slabs form over these weak grains, they could trigger easily and break widely. Look for natural small avalanches and cracking in the snow as a sign that you could trigger an avalanche. Travel on slopes under 35 degrees and steer around steep lee start zones, convexities, and slopes above creeks and cliffs.

    (2/9/2021) This widely breaking slab was observed at Paradise on Monday (2/9). [6500' E aspect. Photo: Porter Michaels]

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    It honestly feels like we’ve been talking about persistent slabs in the West South forever. But, there’s a good reason for that. Avalanche observations continue to trickle in from areas around the zone. Most recently natural large avalanches were observed in the Sourdough Range (White River area) and Coal Creek Ridge (Goat Rock Wilderness). This layer truly continues to “persist” in the snowpack. As we head into another round of storm, consider how much confidence you have in the snowpack. This seems to be shaping up to be a classic low-likelihood/high-consequence scenario. You could travel all day with any obvious evidence of unstable snow, however, this should not overshadow the lengthy list of avalanches, well-documented snowpack structure, and sudden snowpack test results. The simplest way to manage this challenging problem is to choose simple terrain where you can avoid large open startzones.

    (2/6/2021) This slab was intentionally triggered by a small cornice drop on Saturday (2/6) in the Crystal backcountry. It propagated widely and is believed to have run on the Mid-January crust/facet combo. [E aspect, 6300'. Photo: Jeremy Allyn]

Avalanche Discussion

Expect locally higher danger near Mt St Helens and Mt Adams, where more snowfall is expected.

While you are most likely to encounter new wind slabs, it’s the deeper persistent issue that continues to demand our attention. Avalanche activity seems to have quieted down in the West South zone over the past few days, but don’t let that fool you. The lengthy list of natural, human triggered, remotely triggered, and explosive triggered avalanches is compelling. Additionally, a similar snowpack structure exists across much of the Washington Cascades. In other zones, the same weak layers resulted in notable near-misses and an avalanche fatality. (See the short video in the media gallery below for more information) Nothing in the recent weather nor snowpack observations suggests this layer significantly gained strength. 

You can track this layer by digging in the snowpack. You may find a reactive interface about 2 feet (or more in the south part of the zone) below the snow surface. This layer (2/1) continues to demonstrate the ability to propagate a failure and create avalanches. Slightly deeper, a layer of facets over the mid-January crust has been the culprit in most recent slides. It doesn’t really matter which layer you trigger, both can produce large and dangerous avalanches that break widely across the terrain. You can help us track these persistent weak layers by submitting snow profiles and avalanche observations to our public page. 

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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