Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You could trigger a large, 3-4 foot thick avalanche on steep slopes. Recently wind-drifted terrain is the most dangerous. You could also trigger a slide in sheltered areas and at lower elevations near the valley floor. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

Avalanche problems

  • Persistent Slabs

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

    Triggering a 3-4' thick persistent slab avalanche is possible on many slopes. Persistent weak layers (sugary facets, surface hoar, or crusts) exist on most aspects and elevations. The recent storm added to the slab everywhere, and the weak layers are widespread. This means you could trigger a large, dangerous avalanche on just about any steep slope you encounter, even at lower elevations and in terrain sheltered from the wind.

    Persistent slabs are tricky. While recently wind-loaded slopes are likely more dangerous, you can't simply look for and avoid obvious wind drifts. The slab is harder and denser near Banner Summit than in our other zones, making it a little less sensitive to triggering by skiers and snowmobilers. This means you may not experience as many obvious signs of instability like snowpack cracking or collapsing. However, when you do find the "sweet spot" remember that you could trigger slides remotely—from gentler terrain above, below, and to the sides of steep slopes. These avalanches may break wider than expected or higher on the slope above you. 

    Unfortunately, avoiding slopes steep enough to slide is the only way to effectively manage this problem. Skiing or riding steep, consequential terrain remains a risky roll of the dice.

    (12/12/2022) In the Banner Summit zone, the weak November snow is buried beneath a 3' thick dense slab. 

Avalanche Discussion

Last weekend's storm spurred AVALANCHE WARNINGS and a rare EXTREME danger rating. Dozens of avalanches impacted the urban interface. Slides blocked roads, dammed rivers, and piled up against cars and buildings in the valley bottom. To keep track of it all, you can read a summary of the most impactful activity on our Conditions Blog (here). We'll update this post as we continue to gather information about the storm. 

Now it's time to turn our attention to what's next. The storm buried a widespread weak layer and added stress to a second widespread weak layer near the ground. You can clearly see both of these layers in an image of a large avalanche just outside of the Bald Mountain ski area boundary (here). One layer is visible near the skier's waist and the other (which formed the bed surface) is at the skier's feet. As we sort through avalanche observations we're finding that some released in the upper layer and some released on the lower layer or in many cases (like in the photo shown) it was a mixture of the two.

I bring this up simply to underline the fact that the combination of these weak layers is causing unusually widespread dangerous avalanche conditions. It doesn't matter which layer releases, the resulting slide will be large enough to bury injure or kill you. Fair weather today and on through the weekend will test all of us. Don't let the allure of soft turns and sunshine draw you into inappropriate terrain. Recent human-triggered avalanches, widespread poor snowpack structure, and continued cracking and collapsing suggest that we can't outsmart these slides with micro-scale route finding.  Being lucky is not a good travel plan, but giving yourself a buffer in the terrain to manage surprising avalanches is.

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