Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The potential for deep and destructive avalanches lingers, especially in areas east and south in the zone. Warm overnight temperatures and another round of strong solar radiation Thursday will maintain concern for wet avalanches and cornice fall. Approach terrain with a conservative mindset, and avoid travel on or below large open alpine slopes steeper than 35 degrees.

Problèmes avalancheux

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    3

    Neighboring zones to the south and east continue to report recent very large avalanches failing up to 10ft+ deep on the mid-January persistent weak layer. Additional evidence of deep slab avalanches in the West Central was confirmed Tuesday with aerial photos of very large avalanches from last week's cycle. The weight of just a person may not be enough to cause an avalanche on this layer, but big triggers like cornice fall or surface avalanches in motion have us concerned. 6000ft freezing levels overnight and another day of strong solar radiation Thursday are raising uncertainty and adding complexity. Continue to dial back your terrain selection and build in a wide margin for error. Seek out simple, lower angled slopes and avoid going into, or underneath open or sparsely treed terrain with large start zones above you.

    (3/2/2021) Aerial photo of a very large natural avalanche in the Benchmark/Fortune Mountain area in the southern portion of the West Central Zone. Photo: George Coiner

  • Cornices

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    Cornices will require extra caution on Thursday. These unpredictable features loom in many upper elevation areas and will weaken in the strong March sun. If they fail, they could act as huge triggers on slopes below and result in very large and destructive avalanches. Give cornices a wide berth while traveling along ridgelines, and avoid exposure to all cornice features above. Recent deposits of wind-blown snow may still need additional time to settle and stabilize. Continue to steer around large wind-loaded slopes greater than 35 degrees, especially at upper elevations.

    (2/24/2021) Cornices have grown large over the past several weeks like this example near Del Campo Peak.

  • Loose Wet

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

    Another warm, sunny day will maintain the potential for loose wet avalanches on all aspects. Of most concern are steep sun-exposed slopes and upper elevation areas experiencing above freezing temperatures for the first time. Rollerballs and pinwheels indicate snow surfaces are wet and weak and that slopes are primed for loose wet avalanches. Steer away from terrain traps like gullies or slopes above cliffs that magnify the consequences of even a small avalanche. Keep in mind that wet loose slides in motion could even trigger slab avalanches. Seek out lower angled and supported terrain to reduce your risk. 

    (3/3/2021) Rollerballs and pinwheels on a steep sun-exposed slope in the Finney/Segelesen Creek SnoPark area. Photo: Irene Henninger

Avalanche Discussion

Several adjacent zones are in a prolonged period of unstable conditions with continued natural and human-triggered avalanches. Observations are limited, but similar conditions are suspected in the West Central, especially in the southern and eastern portions of the zone. The deep slab problem continues to pose high consequences and demands a conservative approach to terrain and travel choices. Non-freezing temperatures overnight are concerning and more sunshine Thursday will make matters worse. Stay observant, and keep your eyes peeled for signs of instability.  

Reports of impressive deep slab avalanches continue to trickle in, including very large naturals from last week on Benchmark and Fortune Mountains just north of Stevens Pass in the West Central Zone.  On Monday, WSDOT avalanche teams triggered an 8ft deep D3 avalanche on the southeast face of Rock Mountain east of Stevens Pass, along with several D2 soft slab and wet loose avalanches. On Sunday, a natural D3.5 occurred in upper-elevation north-facing terrain in the Chiwaukum Range as well as another D3.5 natural on Chair Peak in the Snoqualmie Pass zone. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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