Bulletin d’avalanche

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You're most likely to trigger avalanches on slopes where the wind has formed drifts or stiffened the snow surface. Large avalanches are also possible in steep, wind-sheltered terrain and at lower elevations. Avalanches may be triggered from long distances away from steeper slopes. Smaller loose snow avalanches may release this afternoon on steep slopes that face the sun. 

Problèmes avalancheux

  • Persistent Slabs

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

    Yesterday, professionals traveling near Galena Summit experienced booming collapses involving weak snow near the ground and chose to avoid avalanche terrain. Most slopes here harbor the same dense, 2-3' thick slab of snow sitting on top of a layer of weak snow (sugary facets, surface hoar, and crusts with facets on top). The possibility of triggering an avalanche involving this snow is not one you should ignore today. You may not get the direct feedback (collapsing) that these skiers did, but rest assured the weak snow is there.

    These avalanches are more likely in areas where recent winds have built slabs, but are possible in terrain sheltered from the wind as well, even at lower elevations. Be thinking about this problem from the time you leave your car until you get back. We commonly deal with weak snow here in Idaho, but the widespread nature of this layer is unusual.

    Avoiding this problem entirely requires you to avoid avalanche terrain. You won't trigger a slide on every steep slope today, but by entering avalanche terrain you will be taking that risk. Avalanches can be triggered from a distance away from steeper slopes and may break wider than you might expect.

    ADDITIONAL DISCUSSION: Extreme wind over the Solstice built sensitive slabs on some slopes. You're most likely to find them at middle and upper elevations but they also exist on isolated slopes down to the valley bottom. Drifts may still be sensitive to your weight where they sit atop a weak surface of crusts, facets, and/or surface hoar. 

    Significant complexity exists in our snowpack. Read the Forecast Discussion below for more details.

    (12/22/2022) A very large natural avalanche occurred during the Winter Solstice wind event over Farley Lake. E @ 9,700'.

Avalanche Discussion

UNCERTAINTY, UNPREDICTABILITY, COMPLEXITY, and YOU

I'd love to be able to give you the gift of a simple, stable snowpack for Christmas. Instead, you'll have to settle for this Christmas poem and some well-above-average temperatures... I guess we rarely get exactly what we want. We roll into Christmas with a significant amount of "weirdness" in our snowpack. I'm not sure there is a better way to put it. The past week delivered frigid temperatures, wind gusts in the 100s MPH, and now rising temperatures hovering near and above freezing. This whiplash-inducing weather is keeping the snowpack on edge and is creating significant uncertainty and unpredictability for us as forecasters and backcountry travelers. 

Let's take a broad look at our snowpack, from top to bottom:

  • UPPER: strong to extreme winds and new snow built stiff, hard drifts in many locations and produced a widespread avalanche cycle just 4 days ago. Additional snowfall and lighter winds built another round of softer slabs on top of these drifts and masked some of the older drifts. Warm temperatures and direct sun today will bring on the chance for small wet snow avalanches and will be changing the properties of the snow in the upper snowpack. Sound complex? Read on.
  • MIDDLE: several layers of surface hoar, facets, sun crusts, and even a rain crust sit 6-24" below the snow surface. In my travels the past two days, I experienced collapsing involving these layers and repeated unstable snowpack test scores (observations here and here, photo here). Some of the wind slabs that were deposited earlier this week broke wider than you might expect, indicating the involvement of one of these weak layers.
  • LOWER: everything I've described above is taking place on top of a widespread layer of weak snow. This layer is impressive, both in the number of avalanches it has produced already (hundreds and hundreds) and in its widespread nature (it exists just about everywhere). Snowpack collapsing is decreasing in frequency, but we have yet to go a day without a report of large, booming, rumbling collapses. On steeper slopes these collapses would result in avalanches. 

How do we deal with this messy picture? I will echo the great advice that Ethan gave you yesterday: your best bet is to remain conservative in your terrain selection. We aren't trying to scare you and we aren't trying to prevent you from having fun. Our goal is to help you get home safely at the end of the day.  Help us to help you by letting us know what you are seeing out there. Thank you, and Merry Christmas. 

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