Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Thu
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dangerous avalanche conditions exist, and the snowpack needs time to adjust to the recent heavy loading event. You can easily trigger large avalanches on slopes 35 degrees and steeper, especially in wind-loaded areas. Choose low-angle terrain and minimize exposure to large open slopes above.

Problèmes avalancheux

  • Wind Slabs

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

    The Mountain Loop area received several feet of snow since Friday, and strong south and west winds blew over the past 48hrs. The most dangerous avalanche conditions continue to exist in wind-loaded terrain where the potential for very large avalanches lingers. Natural avalanches even remain possible. Cornices have grown recently and could drop onto slopes below, acting as huge triggers. Pay attention if you transition into wind-affected terrain, and look and feel for sudden changes in snow surface texture and hardness. Carefully assess recent and wind-blown snow using hand pits and test slopes, looking for easy fractures and shooting cracks. Avoid large wind-loaded slopes 35 degrees and steeper and minimize exposure to overhead hazard.

    (2/22/2021) Natural avalanches on Shuksan Arm breaking 2-3ft+ deep and hundreds of feet wide. Photo: Ben Williamson

  • Deep Persistent Slabs

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

    Observations are limited in the West Central, and high uncertainty exists regarding the mid-January persistent weak layer in this zone. The deep slab problem appears to be waking up in the adjacent Stevens Pass Zone with reports of recent very large natural avalanches failing on the mid-January persistent weak layer. Similar conditions may exist in the Mountain Loop area. Give this scary problem a wide berth and continue to avoid travel on or below large steep open slopes at upper elevations.

    (2/20/2021) This deep avalanche likely failed on the mid-Jan crust Saturday in the Stevens Pass Zone (S, 4900ft). Photo: Wash DOT NCR.

Avalanche Discussion

Expect clear and dry conditions Wednesday morning before the next round of heavy precipitation returns late in the day. New snow still needs time to settle and stabilize, and a conservative approach to terrain is recommended. Cold, low-density snow will see sunshine for the first time following a multi-day storm event. Expect the sunniest skies and the best chance for solar-triggered loose avalanches in the morning before high clouds move in by the afternoon. Be sure to carefully evaluate the snowpack as you travel. Watch for recent avalanches and steer clear of similar slopes. 

A widespread natural avalanche cycle occurred Sunday through Tuesday with D3+ avalanches reported throughout the Stevens Pass, Snoqualmie, and West North Zones. Most impressive were the numerous very large natural avalanches along the Hwy 2 corridor. A very large natural avalanche hit Hwy 20 outside of Newhalem near Gorge Dam. Avalanches on Shuksan Arm were also impressive, breaking 2-3ft+ deep and propagating hundreds of feet wide. The amount of recent and wind-blown snow is concerning enough, and the mid-January persistent weak layer may still be capable of producing very large and surprising avalanches.

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.

Régions couvertes