Bulletin d’avalanche

East Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Wed
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

Yet another day of warm temperatures and light rain will maintain dangerous avalanche conditions. You can trigger very large, destructive wet avalanches that fail on weak layers deep in the snowpack. Continue to choose conservative routes on low-angle terrain and avoid overhead exposure to large open slopes.

Problèmes avalancheux

  • Wet Slabs

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

    Avoid traveling on or near large, steep terrain features. Give yourself large margins of safety from potential runout zones. One of these wet slab avalanches could run further and break wider than you may expect. Remember that wet snow packs a lot of force, and a wet slab gains momentum quickly.  Multiple days of very warm temperatures and nights without a solid refreeze of the snowpack leads to prolonged periods of instability for wet slab avalanches. In addition, their unpredictable nature makes them particularly difficult to manage. Even after peak precipitation, wet slabs can fail as water continues to drain through the snowpack. We may have reached peak temperatures on Monday, but the weather will be slow to cool, and additional light rain or even afternoon sunshine certainly won't help hold the snowpack together. Cornices may fail and trigger slabs on the slopes below them, or glide avalanches involving the whole snowpack may shear off smooth rock faces or steep grassy slopes. Smaller and more predictable wet loose avalanches may also be widespread and could step down to the weak layers of concern.

    (1/27/2024)

    A very large (D2.5) wet slab avalanche that likely ran on January 26th. NNW aspect in Ahtanum Meadows.

    Photo: Joseph Labernik

Avalanche Discussion

With scary, hard-to-predict wet avalanches, remember that until the snowpack experiences below-freezing temperatures, the potential for very large wet slabs remains. Unfortunately, freezing levels will be slow to cool on Tuesday, and we don't expect the cooling to be enough to reduce the likelihood of avalanches. The peak of natural avalanche activity has likely already occurred, but the danger remains quite real in the East South.On Sunday, we were out in the S. Fork Manatash Creek Drainage and saw widespread evidence of the recent warming and subsequent wet avalanche cycle. Wet loose avalanches were widespread, and I found an older slab avalanche that likely ran on a persistent weak layer earlier this month. A snow profile at 6200ft on a northerly aspect revealed a mostly dry snowpack. Although evidence of pooling on lower interfaces means drainage channels had formed, this only allows water impact and weaken a layer of faceted snow and surface hoar above the Solstice Crust. This problematic layer showed a likelihood for propagation in a snowpack test and has been the layer involved in widespread wet slab avalanches throughout East Central and East South. This is a good reminder that the prolonged warming has only prolonged the instability of these weak layers. Human-triggered large to very large wet slabs at Mission Ridge and near Stevens Pass are indications that even as natural avalanche activity decreases, you can still trigger one of these destructive avalanches. Saturday was also very active in other nearby zones, including the West South, where multiple large wet slabs ran naturally at Crystal Mountain, Mt. Rainier, and Mt. St. Helens. Consider the consequences of overhead hazards or triggering one of these deadly avalanches when choosing terrain. If you get out, let us know what you see by submitting a public observation!

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