Bulletin d’avalanche

East Slopes North

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

Expect dangerous avalanche conditions on Friday. Strong winds, recent snowfall, and weak layers in the snowpack are a recipe for large avalanches. You may be able to trigger avalanches that break widely across terrain or come down from overhead. Avoid traveling on or under steep slopes until the snow has a few more days to adjust.

Problèmes avalancheux

  • Wind Slabs

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

    The most dangerous locations will be steep, leeward slopes near ridgetops at mid and upper elevations and large avalanche paths in the eastern portion of the zone. Avoid traveling on or under slopes steeper than 35 degrees, particularly where you see blowing snow or find recently formed wind slabs.

    Strong westerly winds formed reactive wind slabs on Thursday. Winds will shift to northerly overnight and begin to taper off during Friday. Watch for obvious signs of danger like blowing snow, cracking in the snow, and recent avalanches. You may still be able to trigger small avalanches in steep, wind-sheltered terrain. The sun could initiate small loose avalanches on sunny slopes. While getting caught in a wind slab is bad enough, avalanches could be deadly in the eastern mountains. See more below. 

    (1/7/2024)

    Even with little new snow, a natural wind slab occurred between 1/6-1/7 near Harts Pass.

    Photo: Jason Davis

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–2.5

    Dangerous persistent slab avalanches are possible in the eastern mountains. These avalanches can be surprising, and they can break widely across terrain features. You can trigger them from below or from long distances away. You can stay safe by putting a large buffer of terrain between you and large open slopes 35 degrees and steeper. Only expose one person at a time to avalanche terrain. Stop and regroup in safer areas, well away from and out from under any steep slopes. Watch for obvious signs of the danger like cracks shooting through the snow and whumphing collapses. 

    You can find weak crust/facet combination 2-3 feet below the surface. The further east you are from Washington Pass and the Cascade crest, the weaker and shallower the snowpack will be. Observers have reported whumphing collapses and other signs of these avalanches on Delancey Ridge. On the 9th, a number of natural avalanches likely ran on old weak layers near Cutthroat Lake (see photo). At this point, those locations make up the western boundary of this problem. All of the recent snow is stressing underlying weak layers. 

    (1/10/2024)

    Crowns from multiple natural avalanches near Cutthroat Lake. NE, ~6,800ft. Size D2.

    Photo: Chris Bartram

Avalanche Discussion

Observers report recent storm snow heights of about 2 feet since the 8th. On Thursday, observers on Delancey Ridge and near Cutthroat Lake triggered small avalanches in recent storm snow and and fresh drifts. Most other reports of recent avalanches are size D1-2, involving the storm snow. On the 10th, observers reported a number of large, natural avalanches over 2 feet deep near Cutthroat Lake (NE, ~6,800ft) that may have run on a crust from December 30th. Observers on Delancey Ridge reported over 20 rolling collapses at all elevations on a similar crust/weak layer that developed during the prolonged dry periods in December. 

"Weak and variable" sums up the snowpack. While you may find up to 6 feet of snow on the ground at upper elevations near Washington Pass, the snowpack is significantly weaker as you move east of the Cascade crest. There are several decomposing crusts and layers of sugary facets that developed throughout December. In some locations, these layers present as individual prominent bands; in others, they all meld together. Near and west of the Cascade crest, crusts are typically thicker and more stout, and the snowpack has fewer weak layers. On the 7th, NWAC staff went near Cutthroat Lake and found near-surface facets forming on south aspects. Crusts (Dec 30th and Dec 5th) with weak, faceted snow below and above failed on isolation in snowpack tests in the upper snowpack.

Even with the recent snow, coverage remains thin at lower elevations and in the eastern mountains. Watch for hitting rocks and logs or falling in open creeks.  If you're in the mountains, let us know what you see. Submit an observation here!

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