Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

While not likely, you could trigger a very large, 3-foot thick avalanche—the resulting slide would likely be unsurvivable. Reduce your odds of triggering one of these beasts by avoiding steep, rocky, wind-affected terrain. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes. 

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    Our area continues to be plagued by a layer of faceted snow—in this zone, it's buried beneath a dense slab more than 3' thick. Since it was first buried in December, we've recorded nearly 400 avalanches—the vast majority broke on this persistent weak layer. Around 20 of these were human-caused. To say this layer has a poor track record is a bit of an understatement.

    The good news: triggering an avalanche in this zone is less likely than in other portions of the forecast area. Bad news: if you were unlucky enough to trigger a deep slab avalanche, it's unlikely you'd survive the ride. It's the classic low-probability, high-consequence scenario.

    Trigger points are an important consideration with deep slab avalanches. You can reduce your chances of tickling the beast by avoiding slopes with shallow areas where you can more easily impact the weak layer. Trigger points are most common in alpine (or alpine-like) terrain:  very steep (over about 35 degrees), rocky, and wind-affected. Pay attention to what's below you—look for trees, rocks, gullies, and other terrain traps. 

    (1/18/2021) This very large avalanche occurred in our Banner Summit Zone, likely during last week's storm. Based on the depth and appearance of the crown it probably failed on facets buried deep in the snowpack.

Avalanche Discussion

FAQ's regarding the current avalanche conditions...

Q: Where are conditions most dangerous?A: The last storm produced the most widespread avalanche activity in the Galena Summit & E Mtns and Sawtooth & W Smokys zones, but natural avalanches occurred across the forecast. Where the slab thickness above the weak layer is around 2' seems to be the "sweet spot"—these are the areas where you are most likely to trigger a slide.

Q: Are there areas where conditions are less dangerous?A: In the Banner Summit zone, the weak layer is buried beneath a very dense,  3+' thick slab. This makes it more difficult for your weight to affect the weak layer, but if you were to trigger a slide, the consequences would be disastrous. The mountains above Hailey and Ketchum have received less snow this year, and instability is generally limited to where the wind had formed thicker drifts above the weak layer.

Q: Is it getting better?A: Yes. But the tougher question is by how much? With an especially bad persistent weak layer like this one, there are no clear indicators of when the risk of triggering an avalanche has decreased to an acceptable level. Some important clues include decreasing signs of instability such as collapsing and cracking and a prolonged period with no new loading from snowfall or wind. The consensus amongst local avalanche professionals is that we're not there yet.

Q: What should I do about it?A: Glad you threw me an easy one. With no clear answer about how much the snowpack has stabilized, we need to offset the uncertainty with a healthy margin of safety in our terrain choices. In simple terms, this means continuing to choose conservative, lower-angled terrain that isn't threatened by steep slopes from above.

Q: What happened this past week?A: Funny you should ask. Be sure to check out our latest Weekend Update where I attempt to answer just that.

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