Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

 The avalanche danger will increase as the day progresses. We're in the middle of a dangerous wet avalanche cycle due to the first major warm-up of the spring. 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

    Avoid traveling on or under steep slopes where you see signs of instability, like rollerballs or wet avalanches. If snow becomes wet and weak, 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. Loose avalanches or any of these types of falling snow could trigger more dangerous slab avalanches.

    The strong sun and three days of warm temperatures are sending meltwater into the snowpack. Overnight freezes will be minimal. Our uncertainty is high. We know that conditions will be dangerous and wet avalanches will occur naturally, including some that will be big enough to bury a person. However, we don't know how many avalanches will be large versus small. We also don't know if more dangerous wet slab avalanches will occur. Give yourself low-angle and shaded terrain options to 

    (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 trigger slab avalanches.

    Avalanches running on deeply buried weak layers could be 4ft or deeper and propagate widely across a slope. You won't get signs of instability. Your best bet is to remain aware of the terrain around you, staying out of complex alpine terrain and unsupported slopes or those with wet loose avalanche or cornice fall hazards. You can find a thin layer of softer facets over a hard crust, about 3.5-4.5 ft below the surface at upper elevations (above 6,000ft) and further east in the zone.

    (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

Loose wet avalanches have been gradually ramping up over the last several days. Wet loose activity was reported on a variety of aspects near Stevens Pass on Thursday through Saturday, with some up to size D2. Observers reported a deeper (D2.5) slab avalanche that likely occurred on 3/15 in the Chiwaukum range, NW, ~6,6000ft. While the weak layer is unknown, 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 moved into the upper foot of the snowpack.

While we know conditions are dangerous, NWAC forecasters are highly uncertain about when and where the most dangerous avalanches will occur. The best way to deal with uncertainty is to time your travel to exit consequential terrain early in the day and to reduce your exposure to overhead hazards.

From March 9-13th, Stevens Pass picked up 1.71” of precipitation. Strong winds redistributed snow onto leeward aspects with signs of transport observed in wind-affected areas. There were three notable slab avalanches reported in recent snow last week. On Wednesday, two separate skier-triggered avalanches were reported. One was reported to have failed at a surface hoar layer over a crust that was likely buried on the 9th. Both were about 12” deep, and one was triggered remotely. A large natural wind slab avalanche was reported on a leeward, east aspect around 5000’ just outside of the Steven Pass Mountain Resort boundary. It probably occurred overnight on the 11th.

We're in an extended stretch of unseasonably warm, sunny weather. It will be the first big, spring-like warming event of the year, with high temperatures in the 50’s and freezing levels over 11,000’. Very warm conditions through the weekend could produce significant slab and loose snow avalanches.

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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