Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Avalanches are most likely in areas where wind loading has formed drifts or stiffened the snow surface. Although less likely, avalanches are still possible in areas sheltered from the wind. You could trigger slides remotely—from flat terrain below, above, and to the sides of steep slopes.

Yesterday, snowmobilers remotely-triggered a large avalanche, in the Salmon River headwaters. One rider was caught, carried, fully buried, and successfully recovered. Read the Forecast Discussion for more information. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    You are most likely to trigger a large, persistent slab avalanche on steep slopes with recent wind loading (like this one). Wind loaded slopes are most commonly found at upper elevations. Triggering an avalanche is less likely—but not out of the question—on steep slopes that are completely sheltered from the wind. The slabs in question rest above a variety of weak layers (facets, surface hoar, and crusts + facet combinations), and these layers are widespread.

    You may not see obvious signs of instability - such as cracking and collapsing - which makes identifying this problem tricky. Don't assume that a lack of obvious warning signs means stable conditions.

    Avoiding steep, wind-loaded slopes can significantly reduce your chances of triggering an avalanche. Persistent Slabs can release in surprising ways, break wider than expected, and release above or hundreds of feet away from where they are triggered. Tracks on slopes do not equal stability as these slabs may be triggered by the first, third or tenth person on the slope.

    Additional Discussion: You may be able to trigger wind slab avalanches that formed near ridgelines and in cross-loaded areas on the sides of gullies. The size and chance of triggering these slides increase significantly as you climb into windier, alpine terrain at upper elevations. These avalanches could step down to the buried weak layers described above. Look for large cornices, snow pillows, dunes, and ripples, and feel for stiff snow under your feet or sled. These are signs the wind has been at work transporting snow.

    (1/4/2025) Snowmobilers remotely triggered this very large avalanche in the Salmon River headwaters. One rider was caught, fully buried, and successfully rescued. The crown is on a NE aspect near 9300'.

Avalanche Discussion

Yesterday afternoon in the Salmon River headwaters, a group of three snowmobilers remotely-triggered a very large avalanche several hundred feet below where the avalanche originated. The resulting slide caught, carried, and fully buried one of the riders. The rider deployed his airbag and was carried through trees. The other riders located the buried rider and extricated him from the debris in approximately 15 minutes. He was alert when he was evacuated to a local hospital for evaluation. Initial reports suggest the avalanche occurred on a NE aspect near 9300’ in elevation, was several hundred feet wide, and was over three feet thick. We will have more information in the coming days.

We are very grateful that all parties involved are alright. This avalanche illustrates the current low likelihood-high consequence nature of the persistent slab problem in this zone; your odds of triggering an avalanche are slowly decreasing, but, if you do trigger one, the consequences could be severe.

These slabs come in a variety of thicknesses throughout the forecast region, but we can distill them into two general flavors:

  • In areas where the slab is less than about 3 feet thick, the hazard is more obvious. You may observe obvious signs of instability like cracking, collapsing, and recent avalanches.  Shallower snowpacks are most commonly found in the Soldier, Boulder, and Pioneer ranges, as well as the mountains around Ketchum and Galena Summit.
  • In areas where the slab is thicker than about 3 feet, the hazard is less obvious. You may not see obvious signs of instability. While persistent slab avalanches are getting harder to trigger in these locations, the resulting avalanches are expected to be very large. You may not get any clues before triggering one of these large, destructive avalanches. Deeper snowpacks are most commonly found in Banner, the Western Smokys, and the Sawtooth ranges.* The eastern flank of the deeper zones (Banner, Western Smokys and Sawtooths) is still shallow and may act more similar to the other shallow areas.

So how do we operate under these conditions? Proceed with caution and approach the mountains with the assumption that avalanches are possible on many aspects. Take note of differing surface conditions and, especially, wind-affected slopes. Manage your group by riding or crossing steep slopes one at a time, and consider avoiding areas where terrain features like gullies, cliffs, or dense trees could increase the consequences of a slide.

Regions covered