Boletín de aludes

West Slopes Central

Northwest Avalanche Center
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Peligro de aludes

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

Lo esencial

Snowfall and strong winds will elevate avalanche danger through the day and overnight as a storm brings winter back to the Cascades. Move towards lower angle, wind protected terrain as conditions deteriorate. If heavy snowfall arrives earlier than forecast anticipate a faster rise in avalanche danger.

Problemas de aludes

  • Wind Slabs

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

    The threat of wind slab avalanches will hinge on the amount of new snow that comes down during the day. Strong winds are nearly guaranteed but without loose snow available for transport there is little in the way of raw material to build fresh slabs. The snow will come  - it’s just a matter of how much and when.

    Blowing and drifting snow will show which slopes are being scoured down to crust versus which are loading up with fresh slabs. The best bet will be to just avoid steep slopes seeing active wind loading. Anticipate rugged weather conditions later in the day that make slope-scale stability assessment a challenging task. The likelihood of triggering a wind slab will increase as you gain elevation. But you might see slabs building below treeline in areas with the highest wind speeds and the most new snow.

    Start looking for reactive new slabs on all aspects, wind loaded or not, if you find 6-8” or more of new snow in wind protected areas. If you start seeing natural avalanche activity then reduce your exposure to large slopes overhead

    By the end of Friday be ready to deal with shallow wind slabs and all around bad visibility.

    Photo: Matt Lubar

Avalanche Discussion

Thursday was a weather pattern transition day with not many folks out in the mountains. Fresh observations were hard to come by - nearly everybody who is still interested in winter is waiting for the next storm to do its thing. Wind speeds slowly increased through the day and temperatures were on average about 5 degrees cooler than Wednesday.  

The snowpack is typical for spring in the Cascades after four days of high pressure, sunny skies, and some wind. The new snow will fall on a mix of crust and wind hammered snow. Some pockets of soft snow are still hanging on in mid-elevation terrain that is both shaded and protected from the wind. The next round of avalanches should be mostly restricted to the old/new snow interface or within new snow layers. We could always see bigger avalanches triggered by large loads or on a few slopes holding buried layers of surface hoar, near surface facets, or near crust facets.

An observer in Stevens Pass on Thursday triggered a handful of small wet loose avalanches and found punchy spring snow conditions. On Wednesday an NWAC Forecaster at Schriebers/Baker NRA found a number of small but deep wind slab avalanches on west aspects above treeline. They occurred naturally with strong winds and rapid loading Tuesday and released above a sun crust that formed over the weekend and Monday. They didn’t show much reactivity in testing but one slab sticking to a very steep breakover produced a whumph when approached from the side. A team in Snoqualmie Pass the same day found a few wind slabs up high and highly variable snow conditions including crust and lots of wet sloppy snow.

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