Boletín de aludes

West Slopes South

Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 3 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

The most likely location for you to trigger an avalanche will be on wind-loaded slopes. Textured surfaces, fresh drifts, or hollow-feeling snow indicate that wind slabs may exist nearby.  When making travel plans, think about the potential of triggering a very large avalanche on big open slopes.

Problemas de aludes

  • Wind Slabs

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

    Wind slabs are more likely in areas closer to the crest or a mountain gap where easterly winds were stronger on Saturday. Due to the atypical wind direction, slabs may have formed on different aspects than you’re used to. There also likely will be more mid-slope cross-loading. Visual clues such as fresh cornices, drifts behind objects, or textured surfaces can help you identify where the problem exists. They like to form near the base of cliffs, in confined chutes/gullies, or on the leeward side of ridgelines. Slabs should be larger and more reactive as you ascend in elevation or further south in the zone where the storm continued throughout Saturday.

    Feel for density changes in the snow as you travel to help identify older wind slabs that may not be healing as quickly in these cold temperatures. 

    (1/11/2024)

    Small, remotely triggered slab avalanche at White Pass.

    Photo: Dallas Glass

  • Persistent Slabs

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

    This is the problem that should be shaping your travel plans on Sunday. We’ve been talking about weak layers in the snowpack for a while. This past week, these layers have come to life as natural and explosive-triggered slides propagated widely and wrapped terrain features. This isn’t a problem you can tiptoe around. We’ve found a poor snowpack structure everywhere we have dug a hole in recent weeks. The question mark is not about size or distribution but the sensitivity to triggering. Many of these avalanches failed with fairly small triggers, in some cases humans. Going forward, it may take a larger trigger such as a step down or cornice, but don't risk it. Stay off big open slopes where triggering an avalanche on this layer would result in a slide that would likely be unsurvivable. 

    (1/13/2024)

    The crown of a very large avalanche that spanned almost the entire width of Super Bowl near Crystal Mountain. The crown was reportedly 3 feet deep.

    Photo: Dan Royal

Avalanche Discussion

Sunday should deliver fairer weather than what was experienced on Saturday around the West South zone. Snowfall should taper down south with only a few flurries remaining. Sunshine should make an appearance in most locations. But the main story is that temperatures are expected to moderate and the wind diminish. We won't be back to "normal" PNW weather quite yet, so continue to bring those extra layers along with you.

The West South has received over 4 feet of snow in the past week, resulting in multiple rounds of avalanches. Wind slabs, storm slabs, dry loose, and the more dangerous persistent slabs have all been reported from the Crystal Mountain and White Pass areas. We do not have any observations from Government Meadows or the southern volcanoes during this stormy period.  Observations from Saturday are limited. The frigid temperatures may have something to do with that (Chinook hit -19 deg F!). The Mount Rainier Nordic Patrol reported variable travel conditions and plenty of wind-effect as they braved the cold near Paradise. Similar conditions were reported near White Pass. Near Crystal, sensitive slabs were found in wind-loaded snow as well as the crown of a very large avalanche from this past week.

The persistent slabs have been failing on weak layers 4 feet deep in the snowpack - the 12/30 or Solstice Crust. Human-triggered slides occurred last weekend at Paradise and near Crystal Mountain - propagating far distances and wrapping terrain features. On Wednesday and Thursday, Crystal Mountain Pro Patrol triggered several widely breaking slabs during their morning mitigation work. A similar avalanche was reported near White Pass during this same timeframe. Most of these avalanches were categorized as size D2.5-D3. With such cold temperatures, don't expect these layers to heal up anytime soon. Your best management tool is to avoid slopes large enough to produce one of these massive slides. 

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