Boletín de aludes

Stevens Pass

Northwest Avalanche Center
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Peligro de aludes

Wed
Alta montaña
4 · Fuerte
Límite del bosque
3 · Notable
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

Heavy rain and snow are bound to push the snowpack to its tipping point on many mid and high elevation slopes. Wet avalanches of various shapes and sizes are likely to run naturally Monday night through Tuesday. Stay well away from steep slopes and beware of potential for unusual avalanches like glide slabs and debris flows in creek beds.

Problemas de aludes

  • Wet Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Very Likely
    Tamaño
    1.5–2.5

    Very heavy rain is expected to drench the once beautiful powdery, dry snow. Rain on dry snow, especially one with documented weak layers causes concern for wet slab avalanches. Many slopes hold 1.5-3ft of recent snow sitting on buried surface hoar or near surface facets on a slick crust. As rain adds weight and soaks deeper into the pack, slides could propagate widely, and entrain heavy wet debris as they flow downhill.  Because of the shallow snowpack, any large wet avalanche could easily scour all the way to ground, creating an ugly risk. Glide slabs and debris flows could also occur in this type of scenario.

    Slides could be larger and more abundant from higher elevation slopes. Nevertheless, there is potential for slides to run down onto summer trails at mid elevations. At lower elevations we might see smaller but still potentiall dangerous wet loose avalanches from isolated, steep slopes.

    Example very large wet avalanche from last January at Snoqualmie Pass. Photo: Dallas Glass

Avalanche Discussion

As the brunt of the atmospheric river settles in we'll see heavy rain to the tops of the highest peaks in the zone. All bets are off with this event. We don't really know what's going to happen, but it's quite likely we'll see many natural wet slabs and/or loose wet avalanches. A wet and punchy snowpack will make for challenging travel. You could also stumble into falling trees, and raging creeks. The best strategy in this type of event is to wait it out until temperatures cool and the snowpack stabilizes.

Over the weekend, observers found very reactive instabilities beneath the recent storm snow. On Saturday many widespread natural soft slabs were reported, along with widespread shooting cracks and whumphing. Most of the slides ran on a weak interface including surface hoar and/or facets over a slick crust, and propagated impressive distances across entire features. The whumphing collapses came with reports of notable drops, and may be from the crust failing on weaker snow beneath it. Most avalanches were in the D1-1.5 range, with a D2 reported.

The recent storm cycle began on Thursday when light, low density snow covered up various weak layers that sat around, rotting for the latter part of November. These included surface hoar sitting directly on a slick rain crust that extents up to at least 6,500ft. The crust itself ranges in thickness and supportability from stout and slick on due south facing slopes, to brittle and decomposed on northerlies. Before the storm, snow cover was minimal to nonexistent below 4,500ft, especially on sun-exposed slopes. 

If you get out, please let us know what you found by submitting an observation.

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