Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 7 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering avalanches remains a possibility today. You’re most likely to trigger a slide where recent winds have added weight and compacted the snow at the surface, adding stress to the weak layers buried beneath. Avalanches may fail in unpredictable ways and may be triggered from below and to the sides of steeper slopes.

Problèmes avalancheux

  • Persistent Slabs

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

    You’re most likely to trigger a persistent slab avalanche where recently wind-drifted snow sits is stressing the buried persistent weak layers that plague the majority of the forecast area. Surface hoar buried 1-2’ deep has been the main producer of these avalanches so far this year, but depth hoar near the ground has been the culprit weak layer in several large natural avalanches that we’ve observed.

    Yesterday, Sun Valley Heli Ski staff found the “perfect” combination of wind loading and a weak layer when they triggered a slab avalanche large enough to bury a person (photo at right). Read more about this avalanche and what it means in the forecast discussion section below. Persistent slab avalanches can be triggered remotely, from above, to the sides, or below a slope. They fail in unpredictable ways, breaking wider than you might expect and pulling back into lower angle terrain connected to steeper slopes.

Avalanche Discussion

Yesterday in the Western Smoky Mountains, Sun Valley Heli Ski staff triggered a large avalanche while assessing snowpack stability. This avalanche failed on a layer of surface hoar on an E-NE facing slope at 8,600’. This is the same layer that exists across our forecast area and that has produced extensive natural and human-triggered avalanche activity, spanning from the Soldiers up to Banner Summit. Although the angle of the path that failed was in the low 30 degree range, the slab pulled back into terrain above a rollover that was only 26 degrees. Recent winds had loaded this slope, increasing the stress on the weak layers in the snowpack.

If you’ve been reading the forecast regularly, you’ve noticed that the avalanche danger recently dropped from considerable to moderate. You might find yourself wondering how the danger can be dropping if people are triggering avalanches. Avalanche danger is the likelihood of an avalanche to cause damage to something of value (you). And while your odds of triggering avalanches are slowly decreasing, that possibility is still on the table. What does possible look like? Scroll back up the page and look at the photo of the avalanche above.

As you are traveling in the backcountry, you may be seeing fewer obvious signs of instability. Your snowpack test scores may be producing fewer unstable results. Perhaps you are seeing other folks skiing and riding in avalanche terrain without consequences. None of these things mean that the snowpack is now stable; they just mean that it is slightly more stable than it was. You may be a bit less likely to trigger an avalanche today than yesterday, but the consequences of triggering one will be exactly the same. Keep this in mind as you travel in the backcountry today.

Régions couvertes