Bulletin d’avalanche

East Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

0800 update-  Updated to Considerable Below Treeline:

You may observe a wide range of storm instabilities as new snow piles up, but you’ll likely trigger the largest avalanche in locations where the wind will blow new snow into thicker slabs. Be especially cautious at higher elevations on the eastern edge of the zone, where it remains possible to trigger an avalanche failing on old snow near the ground.  Today will be a good day to take a step back and avoid steep slopes as new snow accumalates.  

 

Problèmes avalancheux

  • Storm Slabs

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

    As new snow piles up throughout the day, storm slabs may start developing at all elevations and aspects.  Expect these storm slabs to be touchy in locations where surface hoar or near-surface facets have been buried. Expect larger slabs to develop at mid and upper elevations where moderate to strong WSW winds will redistribute new snow into thicker drifts.  You will find these larger slabs living on the lee sides of ridgelines, below cornices, and scattered at mid and upper elevations.   

    Use hand pits or small test slopes as tools  to assess how the new snow is bonding to the old snow surface.  Tuesday will be a good day to just keep your travel simple- if you observe significant new snow accumulation and the winds transporting snow,  just avoid all steep slopes. 

  • Persistent Slabs

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

    The last known sign of instability involving this layer occurred last Thursday when whumping was observed east of Mission Ridge.  With additional new snow and wind loading, the likelihood remains possible to trigger a larger avalanche failing on this old snow, especially in areas further east in the Wenatchee Mountains where the snowpack is shallower.  Use snowpack tests to identify where this weak, sugary snow exists.  Be extra vigilant when traveling on northerly aspects, consider sticking to lower consequence terrain such as ridges and avoiding steep, open slopes. 

    (12/10/2022)

    3ft deep persistent slab avalanche in a heavily wind loaded area at Mission Ridge

    Photo: Drew Carlton

Avalanche Discussion

Tuesday is shaping up to be another cold and stormy day for the east-central.  Expect increasing avalanche hazard throughout the day on Tuesday, especially in the western parts of the zone where there is higher forecasted precipitation amounts.  Cold temperatures will likely enhance precipitation amounts, so you may find quite a bit of new low density snow by the time you end your day on Tuesday. With this weather forecast, you may find more avalanche problems than what has been listed, such as loose dry in steep terrain or wind slabs near ridgelines.  It will be a good day to stay on top of your game and use conservative decision making as it continues to dump. 

Monday was quite cold across the east-central with many mountain locations struggling to climb out of the teens.  Snowfall amounts varied across the zone with Lake Wenatchee receiving 7 inches and areas further east only reporting a trace.  One observer in the Tumwater Canyon area reported finding surface hoar sitting on top of a sun-crust, which will create a nasty set-up once a slab forms on top.  In the past days leading up to this recent snowfall, other observers reported finding a variety of weak surfaces on a variety of aspects and elevations ( Trinity & Tumwater Canyon).  Going forward, be sure to check how this new snow is bonding to the old snow surface.  These weak surfaces that were just buried, could be tomorrow's weak layer.  Use quick hand pits or small test slopes to assess how the new snow is bonding to the old snow surface. 

On Saturday, Chelan County Mountain Rescue found a very shallow snowpack with a general lack of slab structure at lower elevations on the north side of Blewett Pass. On Thursday, an observer noted a collapse west of Mission Ridge, along with three slab avalanches, two of which were in unusual locations. Although isolated, it signals that we are not yet done with persistent weak layers buried near the ground. Many locations in the East Central zone have a weak snowpack structure with facets formed in mid-November buried near the ground. Most avalanches on these basal facets were on 12/8 and 12/9, and observed from north and east aspects in wind-loaded terrain near Mission Ridge. One very wide avalanche was observed on the 14th in the East North zone near Twisp (see photo below). Further west, observations indicate that the snowpack is deeper and the weak layers are stronger in the Teanaway and the Salmon La Sac areas.

Thanks for reading! If you are out and about in the mountains, share an observation on the site.

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