Boletín de aludes

East Slopes Central

Northwest Avalanche Center
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Peligro de aludes

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

Lo esencial

There have been numerous accounts of human triggered slab avalanches over the past few days in the zone. A layer of buried surface hoar and faceted snow rests under recent warm storm snow, and you could trigger surprisingly wide avalanches in sparsely treed terrain. You may or may not receive direct signs of instability like long shooting cracks before triggering a slide. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2

    The snowfall and wind may be quieting down, but expect that dangerous conditions with touchy slabs could remain for the next few days. There have been numerous reports of human triggered slab avalanches from over the weekend, and Monday. This bullseye information is hard to overlook.  Some reported that these slides were triggered on lower angled slopes than suspected, and slabs have tended to fracture widely. The majority of avalanches have occurred in the 5,000-6,000ft range and on N-E aspects. However, avalanches have also been triggered on WSW aspects, and instabilities found as low as 4,400ft. Slabs could be anywhere from 1-2ft deep, or deeper in wind drifted terrain. 

    The problematic layers are buried surface hoar, facets and crusts from January 4th, or weak snow on a slick crust from Christmas.  These weak layers could be especially tricky, and in some cases folks have reported minimal signs of instability before triggering a slide. You may not find buried weak snow on every slope, and you may not receive signs of instability while traveling. With this in mind, the safest bet will be to assume theres weaker snow underneath the recent storm snow, and plan to stay on slopes that are not steep enough to avalanche. Sparsely treed terrain may be the most likely place you'll trigger a slab. See the video from Dallas below in the media gallery regarding terrain selection with a buried surface hoar layer. If you do get any long shooting cracks, these are instabilities that should be heeded. 

    (1/8/2023)

    Very wide shooting crack on Tronsen Head at Blewett Pass. This is typical of a persistent slab problem.

    Photo: PKS

Avalanche Discussion

Reports of human triggered slides seem to keep coming in.  The eastern Wenatchee Mountains have been especially active, but slides have been trigged throughout the zone and on a variety of aspects. A small ski triggered slide occurred on Monday at Mission Ridge on a north aspect at around 6,000ft. The skier took a short ride, but luckily was ok. Control teams reported triggering small wind loaded pockets with additional control near ridgetop terrain. WSDOT reported a handful of large natural wet loose avalanches that covered Hwy 2 in Tumwater Canyon during a proactive closure period. 

The recent weather pattern has favored the East Central zone, and we've received a substantial amount of new snow and water weight since about January 4th. That's also when a widespread layer of surface hoar, facets, and crusts were buried. At Blewett Pass over the weekend, an observer reported some slopes not avalanching on Saturday, but the same ones did on Sunday. What changed? The slab kept getting thicker and more cohesive as more snow fell. At this point, most areas have plenty of slab, and weak snow may exist underneath it. More time is needed for instabilities to settle out.

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