Bulletin d’avalanche

East Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
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

Large and destructive wet avalanches will remain possible until the snow surface freezes. Wet slabs could be 1.5-3ft deep, and run on old crust layers and/or the ground as glide slabs. Stick to lower angled and well supported slopes for another day.

Problèmes avalancheux

  • Wet Slabs

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

    We're still easing our way out of a prolonged period of warm and wet weather. This, combined with a weak snowpack structure have created unique conditions for wet slab avalanches. These are running on old faceted and crust layers from December, and/or on the ground. Slides may fracture across terrain features, and carry the entire seasons snowpack with it. Slides may be 2-4ft deep, and could be powerful enough to take out trees. Many avalanches have run on the ground, leaving a mud scar in their wake . Along with these nasty slides, wet loose avalanches may run and scour to the ground, and cornices could break away.

    Although the likelihood is ratcheting down, it's recommended to stick to lower angle and well supported slopes until the snowpack has a chance to refreeze. Higher elevation terrain may have a thin crust on Friday. If you find the crust is supportable, then the chances of triggering a slide drop significantly. Stay out from under cornices that could fall and trigger a large avalanche on the slope below.

    (1/28/2024)

    Very Large wet avalanche that ran naturally on 1/28 in the Icicle River Drainage.

    Photo: Erik Soldenwagner

  • Glide Cracks

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2.5

    Glide (slipping of the entire snowpack) activity has been occurring, and glide avalanches have been observed on a regional scale over the past 3 days. These types of avalanches are not something we talk about too much in this zone, but with these conditions we're seeing them. Glide slabs typically run on smooth bedsurfaces, like rocks and grass.

    Glides could entrain more wet snow and entrain to become larger avalanches. Large, complex terrain features in the lower river valleys tend to funnel slides into gullies, and create deeper debris piles. Stay away from these runout zones until the snowpack has a chance to refreeze.

    (1/30/2024)

    Glide avalanches that entrained wet snow. E at 3,000ft in Tumwater Canyon.

    Photo: Matt Primomo

Avalanche Discussion

Temperatures have begun a slow cooling trend, and the rain is letting up. Light snow may even be falling at some higher elevations. Thursday offered a soggy day, and Wednesday was a wet one for the zone. Many stations throughout the zone measured over an inch of rain in a 10 hour period during the day. In the past week, there have been a couple 'peaks' of instability. One probably occurred on Sunday with the initial warmup and change of the upper snowpack from dry snow to wet snow, and another may have occurred on Wednesday with heavy rain. That said, we're largely in the dark regarding visual observations of upper elevation terrain for the past two days. At this point, water has probably made its way through most of the snowpack, except at some higher elevation locations. This means that water is likely still pooled up at prevous crust/facet persistent weak layers. On Thursday in adjacent Stevens Pass, we found this layer to still be active and showed potential to propagate in tests on a NE aspect at 5,300ft.

On Sunday, Monday and Tuesday, many natural and skier-triggered, very large avalanches (D2.5-3) were reported throughout the zone and in neighboring zones. Slides off Big Chiwaukum and in Tumwater Canyon were running to the ground (see photos below). This may be just the tip of the iceberg, as visibility has been limited. Control at Stevens Pass ski area on Tuesday triggered very large (D3) avalanches that ran on the Solstice Crust 3ft deep. On Sunday, a 2.5ft deep and 200ft wide wet slab was triggered and ran on weak layers near the ground at Mission Ridge. One skier was caught and carried, lost their skis but luckily reported only a knee injury. With nasty, wet avalanches running on the ground, it'll be advised to stay off of steep and unsupported slopes, and away from larger features until the snowpack has time to refreeze. 

Faceted snow over the Solstice Crust was the persistent weak layer involved in multiple skier-triggered avalanches earlier in January, and activity increased as temperatures warmed towards the end of the month. When it began to rain, reports of very large avalanches running on deeply buried weak layers came in from nearly every zone in our forecast area. The overall weak structure of our snowpack has led to the current prolonged period of instability. 

If you get out, let us know what you see by submitting a public observation!

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