Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering a 1.5-2' thick avalanche remains possible on some slopes. Avalanches are more likely on shady slopes facing E-N-W and could occur on both sheltered mid-elevation slopes and in wind-affected terrain. Recent winds have formed thin wind drifts that are likely to be small but could be easy to trigger. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2

    A layer of surface hoar is buried 1.5-2' deep on many shady (E-N-W) slopes. In this zone yesterday, I observed a skier-triggered avalanche that occurred sometime in the past week (photo above/right, details). A number of similar slides have occurred in the neighboring Sawtooths & W Smokys zone. Sun Valley Heli Ski guides observed a natural avalanche in the W Smokys that likely released during the wind event on Sunday (details). On Friday, snowmobilers triggered a slide in Stanley Lake Creek (details). The slope had numerous tracks on it before it finally avalanched. 

    Surface hoar is a tricky weak layer. It can be "spotty" in its distribution—it may exist on some slopes, but not others. You may be as likely to trigger an avalanche on sheltered slopes as you are in wind-affected terrain. In fact, most of the avalanche activity on the surface hoar has occurred in shady, middle-elevation terrain on slopes where signs of wind loading were not obvious.

    You can reduce your risk by avoiding shady slopes (facing E-N-W) that are very steep (greater than about 35 degrees). While the avalanche activity points to the layer being more common on sheltered slopes, I wouldn't rule out its existence on wind-exposed slopes.

    (1/23/2023) Avalanche apparently triggered by a skier on Banner Summit. Slab depth and terrain characteristics are consistent with early January surface hoar layer. 7250', NNW. The date of this avalanche is uncertain, but likely occurred since Jan 18th. Photo taken Jan 23rd.

Avalanche Discussion

We have variable and divergent conditions across our region. This is making our jobs as forecasters difficult, and if you recreate in multiple portions of our forecast area, it means more for you to keep track of too. Here's a (somewhat) brief rundown of how things vary across the forecast area, from north to south:

In the Sawtooths & W Smokys and Banner Summit zones, the primary player is a layer of surface hoar that was buried in early January. The majority of the recent persistent slab avalanches have occurred in these areas. These zones have also received the most recent snowfall, and the layer can be found beneath a stout 1.5-2' thick slab on slopes that face E-N-W. You may be as likely to trigger an avalanche on sheltered slopes as you are in wind-affected terrain. While triggering an avalanche on older, more deeply buried weak layers can't be ruled out in these zones, the more uniformly deep snowpack makes it difficult for our weight to reach these layers.

The Galena Summit & E Mtns zone has a variable and complex snowpack. The early January surface hoar can be found buried 1-1.5' deep, and it produced a few avalanches early on after it was buried. However, it didn't get quite enough load to be a widespread issue, and the surface faceting process is weakening the slab that does exist. The surface hoar layer remains more problematic where recent or past wind loading had created a stiffer slab in the upper snowpack. Adding insult to injury, more deeply buried weak layers are more worrisome here. With a shallower snowpack than further north and west, and more rocky, wind-affected alpine terrain, there are more areas where these weak layers are closer to the surface.

Moving south to the Soldier & Wood River Valley zone, in the mountains above Ketchum and Hailey, plenty of weak snow exists but a strong slab is less common. You can avoid most avalanche hazard by staying off of wind-affected slopes where a stiffer snow surface exists. In the western portions of this zone, including the Soldiers and the mountains around Dollarhide Summit, a much more complex snowpack exists—one that has attributes of all the other zones. Avalanches occurred in the Soldiers on the early January surface hoar layer, and deeper weak layers may remain a concern similar to the Galena Summit & E Mtns zone. Throw in the recent wind events that have hit the Soldiers, and you have a real mixed bag of conditions. 

Regions covered