Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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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 fresh, hard 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. This zone has had the greatest number of both natural and human-triggered slides attributed to this layer. Sun Valley Heli Ski guides recently observed a natural avalanche in the W Smokys that likely released during the wind event on Sunday (photo above/right). Last Friday, snowmobilers triggered a slide in Stanley Lake Creek (details). Since then, observers continue to find this layer in snowpits, but tests are showing signs of improvement.

    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)—especially those with poor consequences of going for a ride. While the avalanche activity points to the layer being more common on sheltered slopes, don't rule out its existence on wind-exposed slopes.

    ADDITIONAL DISCUSSION: Older weak layers (often facets found near crusts, with some surface hoar) exist deeper in the snowpack. These layers are buried beneath dense, 3-4+ thick slabs. While triggering them is unlikely, it can't be ruled out in steep, rocky, wind-affected terrain. 

    (1/23/2023) This natural avalanche in the W Smokys likely occurred during the wind event on Jan 22. The depth and characteristics are consistent with the early-January surface hoar layer. It appears to have been triggered by a small wind slab. 8500', E. Sun Valley Heli Ski photo.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    The ongoing wind event continued yesterday and overnight. Northerly winds tend to be particularly localized and variable. The Upper Vienna station at the head of Smiley Creek recorded moderate to strong speeds from yesterday afternoon through this morning. N-NW winds often make a mess of the Sawtooth alpine terrain. They can create alternating patterns of wind erosion and slabs across cirques and basins, and blow straight up couloirs forming wind slabs in unexpected locations.

    When strong winds blow older snow around, they tend to form wind slabs that are hard and dense. They can often have a "chalky" appearance (photo above/right). Sometimes these hard slabs feel hollow or drum-like, which is a sure indicator that they are sitting atop weaker snow and should be avoided when on a steep slope. In Baker Creek yesterday, Scott encountered a few hard wind slabs yesterday and was able to get one to crack out 20 feet from his skis. While wind slabs are likely to be small, they could send you on a not-so-magic carpet ride if they catch you unaware. 

    (1/24/2023) Recent northerly winds formed hard wind slabs up to a foot thick at exposed ridgelines near 9000' on Fox Peak. The fresh slabs were difficult to trigger, but Scott was able to get one to crack about 20 feet out from his skis. The slabs only extended 10-30 feet below the ridges, but the slabs' hollow sound and feel was "creepy".

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 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 occurred in these areas. These zones 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. Observers continue to find this layer in snowpits, but tests are showing signs of improvement. You may be as likely to trigger an avalanche on sheltered slopes as you are in wind-affected terrain. Triggering an avalanche on older, deeply buried weak layers is unlikely (but not impossible) given the more uniformly deep snowpack.

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, but it didn't get quite enough load to be a widespread issue. The surface hoar layer remains more problematic where recent or past wind loading had created a stiffer slab in the upper snowpack. Although the surface hoar is less concerning in this zone, the older, more deeply buried weak layers are more worrisome. 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 hammered the Soldiers, and you're likely to find a mixed bag of conditions. 

So what should you do? Snowpack weak layers are variable enough in their distribution and sensitivity that attempting a slope-by-slope assessment can be a fool's errand.  As weak layers become less reactive, it usually takes a very steep slope to trigger a slide (over about 35 degrees). Perhaps the biggest distinction you can recognize is that if you are recreating in the Sawtooths & W Smokys or Banner Summit zones, you may be as likely to trigger an avalanche on sheltered slopes as you are in wind-affected terrain. By contrast, in the Galena Summit & E Mtns and Soldier & Wood River Valley zones, wind-affected slopes are far more concerning. 

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