Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

We're approaching the tail end of a long period of very warm weather.  Give the snowpack another day to cool before traveling on or under complex terrain. Time your travel to be off of slopes before they become wet and weak, and beware of avalanches that could come down from overhead slopes.

Problèmes avalancheux

  • Loose Wet

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

    Natural avalanches are still possible especially in steep, rocky terrain or on slopes on the north half of the compass. Avoid traveling on or under steep slopes where you see signs of instability, like rollerballs or wet avalanches. Give yourself options to exit wet, sunny slopes before it's too late. Keep your travel early or move to more shaded or lower-angle terrain.  You could see cornice falls, glide avalanches, or large portions of snow falling off of rock features. Any of these could trigger more dangerous slab avalanches.

    The snowpack has been rapidly melting, and overnight freezes will be minimal. Our uncertainty is high. We don't know exatly how many avalanches will be large versus small. We also don't know if/where more dangerous wet slab avalanches will occur. 

    (3/16/2024)

    Debris from large wet avalanches that occurred 3/15-16.Chiwaukum Range, SW

    Photo: Stevens Pass Patrol

  • Deep Persistent Slabs

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

    Although deeply buried weak layers have been very difficult to trigger, meltwater in the snowpack, wet avalanches, and cornice falls could all cause natural slab avalanches.

    Avalanches running on deeply buried weak layers could be 2-4ft deep and could propagate widely across a slope. Your best bet is to put a large margin of terrain between your group and very large, upper-elevation slopes. Stay out of complex alpine terrain (above 6,000ft), unsupported slopes, and similar areas with wet loose avalanches or cornice fall hazards. You can find a thin layer of softer facets over a hard crust (early February), about 3-4.5 ft below the surface at upper elevations and further east in the zone. Slightly higher in the snowpack, the Feb 24th interface has recently produced propagating test results and possibly some slab avalanches.

    (3/16/2024)

    A very large slab avalanche likely occurred on 3/15. The exact weak layer is unknown.Chiwaukum Range, 6,600ft, NW

    Photo: Stevens Pass Patrol

Avalanche Discussion

On Wednesday, temperatures will be a bit cooler, and there will be more clouds than previous days. However, it will be the sixth day in a row with a minimal overnight freeze. 

On 3/18, NWAC and Stevens Pass Patrol forecasters targeted sun-exposed terrain. They found meltwater pooling 2 feet (72cm) below the surface above the 2/24 crust. Wet avalanche activity was reported on a variety of aspects near Stevens Pass since 3/14, with some up to size D2 and occurring on northerly aspects and upper elevations. A large (D2) slab avalanche occurred on the 17th in Wenatchee Bowl, WNW, 5,550ft , and was about 2 feet deep. Observers reported a couple of deeper (D2.5), widely propagating slab avalanches that likely occurred on 3/15-16 in the Chiwaukum range. While the weak layer is unknown, it appeared to run in an older layer of snow. Observers suspect this avalanche could've been the result of a cornice fall. Observers outside of Stevens Pass resort boundary reported dry snow on north aspects, while on mid-elevation south aspects, meltwater has progressed from the upper foot of the snowpack on the 16th to 2 feet below the surface on the 18th.

Your avalanche, snowpack, or weather observations are extremely valuable to the avalanche community. Help create a more accurate avalanche forecast by submitting your observations here. 

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