Bulletin d’avalanche

East Slopes South

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

While the sun may shine, a significant warm-up and recent heavy wind loading will create dangerous avalanche conditions on Wednesday. Strong winds have created thick, hard slabs of drifted snow on leeward slopes that may remain sensitive to a human-trigger. Wet avalanches could be easy to trigger or may even release naturally on steep, sunny slopes as the day heats up.  Give steep, sunny exposed a good buffer, especially once you notice rollerballs shedding or sticky, wet surfaces under your feet or machine. 

Problèmes avalancheux

  • Wind Slabs

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

    9-13 inches of new snow accompanied by strong SW winds have built thick wind slabs on leeward slopes across the zone. As we observed on Tuesday, these slabs are big enough to be a problem and could be large enough to kill a backcountry traveler. Be on the lookout for these slabs as you start seeing signs on wind texturing or corniced ridgelines. These slabs will often lurk downwind of cornices, beneath rock and cliffbands, on mid-slope convexities, and unsupported features. 

    While small test slopes and hand-pits are excellent tools to use for smaller terrain features, they may not paint the full picture in heavily loaded alpine terrain that harbors bigger hard slabs. The best practice would be to steer around these heavily loaded features for another day or two until these slabs heal. Shooting cracks, drum-like surfaces, or recent avalanche activity are great reasons to head for more simple terrain.

    (2/25/2025) Photo: Crystal Mountain Pro Patrol

    A widely propagating, human-triggered avalanche near Crystal Mountain on Tuesday. This avalanche broke in wind drifted snow. 

  • Loose Wet

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

    New snow, sun, and rising freezing levels are key ingredients for wet loose avalanche activity. It likely won’t take much sun for the snow to react on solar slopes. These could grow large in bigger terrain features. Wet snow avalanche problems are typically most reactive on the first warm days. I wouldn’t be surprised if we see a few large natural wet loose in steep, sunny terrain as the day heats up. This will be a good day to steer around sun-exposed terrain as the day progresses. 

    (3/21/2021)

    Wet loose avalanches often initiate where snow sheds off rocks and trees onto the slope below. Note that there are both small rollerballs and wet loose avalanches in this image. 

    Photo: Zack McGill - Cascade Mtn Ascents

Avalanche Discussion

The East South did well with this recent storm track. Weather stations reported 9-13 inches of new snow with the highest accumulations reported around Bumping Lake. 

Observations were minimal on Tuesday in the East South, but a couple of key observations trickled in from the neighboring zones:

1). Avalanche professionals at Crystal Mountain in the West South, triggered large hard slab avalanches ( both human and explosive triggered) in wind drifted snow. Some of these avalanches featured wide propagation and broke several feet deep. They also reported sensitive storm slabs in more sheltered terrain.

2). A backcountry skier traveling in Icicle Creek outside of Leavenworth in the East Central zone, reported a large natural avalanche that broke into old snow (likely the 2/13 weak layer). This avalanche occurred in a wind-loaded location ( NE @ 6600 ft)

While these are not from the East South, we suspect a similar snowpack structure exists in the zone, especially in areas closer to the Cascade Crest that recieved more new snow. Check out the photos in the gallery for more info. 

Wednesday will offer plentiful sunshine but recognize it marks the first warm day after a stormy period that brought significant avalanche activity. New snow doesn’t like rapid change and we’re about to see a rapid warm-up on Wednesday. While some slopes may offer great riding conditions, others could be problematic, especially those slopes that receive significant solar input. You can increase your margins by easing into terrain slowly and avoiding slopes that show signs of warming or recent wind loading. 

Avalanches breaking on old weak layer 2-3 ft below the surface have likely trended unlikely since our significant rain event, but keep in mind it's not impossible as were reminded from the East Central observation on Tuesday. Travel with curiosity and have some skepticism before riding on steep N-E aspects that previously harbored weak structure. Digging a quick snowpit can offer valuable information to help you make more informed decisions before entering steep terrain on this side of the compass rose. 

 

Let us know what you see by submitting a public observation!

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