Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Mon
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 8 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Very dangerous avalanche conditions exist. Destructive natural and human-triggered avalanches are very likely. Stay off of and out from beneath steep slopes. Slides may break wider, be triggered remotely, and run faster + further than expected today.

The backcountry Avalanche WARNING does not apply to the HWY 21 avalanche program.

Problèmes avalancheux

  • Storm Slabs

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

    You are very likely to trigger 1-3 foot thick slabs in both sheltered and wind-loaded terrain today. The size and reactivity of avalanches will increase as you climb into windier terrain above 8000 ft. Avalanches could release naturally, and cornices may fail, triggering slabs on the slopes below.

    Shooting cracks in front of your sled or boards mean you've found a sensitive slab.

    Avalanches could break wider than you expect, be very easy to trigger, and run faster + further where storm snow buried slick crusts, facets, crusts + facets, or surface hoar. Avalanches involving new storm snow will be dangerous on their own, but they also increase the chance of very large avalanches breaking on persistent weak layers buried deeper in the snowpack (Problem #2 below).

    (12/18/2025)

    We found natural avalanches on the NE slope of the summit of Copper Mountain (8900 ft). These appeared to have released yesterday and looked to be thin wind-slabs.

    Photo: Sawtooth Avalanche Center

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–3

    A couple of unstable weak layers exist below 2-4 ft (50-130cm) of snow. Intense loading (snow + wind) during the multi-day storm is actively testing the limited strength of those buried layers. Avalanches involving these layers may be harder to trigger today, but will probably be very large and likely unsurvivable.

    We have continued to see cracking, collapsing, unstable test results, and natural avalanches related to the multiple crust/facet combos that are now tucked under a heap of new snow. It is going to take a whole lot more time for the buried weak layers to adjust to the additional snow load. The most suspect locations for these crust/facet combinations are W-NW-N-NE-E-SE facing slopes at middle and upper elevations (near and above ~8000' in this zone).

    Your best bet to keep out of trouble today is by avoiding travelling on or below steep slopes where you suspect this weak layer to exist.

    (12/20/2025)

    Natural avalanche on an East facing slope at 8900 ft up Beaver Creek in the Western Smokys.

    Photo: Jeremy Lato

Avalanche Discussion

We're back for another round of this hefty holiday storm, and it's coming out swinging today. The Banner Summit zone is expected to receive 2-3" of SWE (14-20" of snow) over the next 24 hours. Expect natural avalanche activity to peak tonight as the rain/snow lines rise and rapidly deteriorate the snowpack's tenuous remaining stability.

Yesterday, many folks capitalized on the clear skies to get out into the mountains, and nearly every report we received included observing big thunderous collapses, long-running cracks, and evidence of a widespread, large avalanche cycle. We're not out of the woods yet, so if you choose to go out in the mountains today, please play it safe.

On Friday, two members of our forecast team were caught off guard when they triggered, were caught, and carried in a small wind slab avalanche above the Baker Lake trailhead (click here for more information).  Fortunately, everyone is alright and the piece of terrain they were travelling on was relatively small. What's tricky about their avalanche is that it was triggered only a few steps off of a wind-scoured ridgeline with sagebrush sticking out. These consequential micro-terrain features can be challenging to read, especially during and after a big dump of snow and honking winds. The take-home we discussed while debriefing this near-miss was to build in bigger margins during these times of high danger.

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