Bulletin d’avalanche

East Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Thu
Alpin
2 · Modéré
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

If you get unlucky you can still trigger a large and surprising avalanche that breaks 1-2’ deep on a layer of buried surface hoar or facets sitting on a crust.  Recent avalanche activity and observations point at these weak layers existing on numerous aspects and elevations, but especially at mid-elevations between 5000-6000 ft in the Wenatchee Mountains.  Wednesday won't be the day to thread the needle, give yourself plenty of space from slopes greater than 30 degrees. 

 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Recent new and wind drifted snow from previous days will continue to stress weak layers 1-2’ deep in the snowpack.  These weak layers of surface hoar and facets on a crust have been responsible for numerous human-triggered avalanches in the past days.  Expect dangerous conditions to exist - especially in the Wenatchee Mountains- despite another day of quiet weather. 

    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. 

    These persistent weak layers are complicated to deal with. You may or may not receive signs of instability while you travel.  If you hear a whumphs or notice a shooting crack, it may just be too late. So, your best bet will be to stick to lower angled terrain and avoid slopes greater than 30 degrees.  

     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

It's been an active few days of avalanche activity across the east-central zone.  Most of the human-triggered avalanches have been confined to the Wenatchee Mountains (5-6,000 ft), however other avalanches have been reported in locations such as the Icicle and Lake Wenatchee.   

The most recent known avalanche on the January 4th layer of buried surface hoar occurred on Tuesday in the Wenatchee Mountains on an NE aspect at 5500 ft.  This avalanche was small (D1), but slabs depths were approximately 1’ deep and clearly failing on a bed surface of feathery surface hoar.  Additionally, observers continue to find these weak layers scattered through the terrain and producing planar results and full propagation in snowpack tests. (Mission / Blewett Pass). 

 All of this information illustrates how we have a complex snowpack across the eastern mountains. You may find less reactive conditions further west, however, it will still be critical for you to look for these weak layers as you move through the mountains.  Observers are actively finding these weak layers on various aspects and elevations. Until things settle out, increase your margins by avoiding avalanche prone slopes. 

If you travel in high elevation shaded aspects, you may still find reactive wind slabs in specific areas.  On Tuesday a skier triggered a small ( D1.5) slab avalanche in wind drifted snow on Mt Cashmere in the Icicle drainage. 

Stay tuned for big weather changes and a sharp rise in avalanche danger on Thursday…

Régions couvertes