Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Wed
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 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. This zone has had the greatest number of both natural and human-triggered slides attributed to this layer. Sun Valley Heli Ski guides observed a natural avalanche in the W Smokys that likely released during the wind event on Sunday (photo above/right). On Friday, snowmobilers triggered a slide in Stanley Lake Creek (details). The slope had numerous tracks on it before it finally avalanched. The surface hoar also exists in the Banner Summit zone, and yesterday I observed a skier-triggered avalanche that occurred sometime in the past week (details). 

    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.

    ADDITIONAL DISCUSSION: There are also deeper weak layers in the snowpack. These layers (often facets found near crusts, with some surface hoar) 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. Slopes like these have variable snow depths, with thinner areas of the snowpack that make it easier for us to impact these deeper weak layers.

    (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

    N-NW winds picked up again yesterday afternoon and continued through the night. These sorts of winds are often under-reported by our stations, so it's difficult to predict the extent of new wind loading. Most observers yesterday reported more wind-affected surfaces than wind slabs, but keep your eyes peeled for fresh drifts today. These will be most common at upper elevations and especially in the alpine. The lack of loose snow available for transport means wind slabs are likely to be small, but they may be able to knock you off your feet and send you downslope if they catch you unaware. Pay attention to the snow you are traveling through, if it is becoming denser or deeper you are probably moving through a wind slab. Cracks shooting out from your skis or machine are clear indicators you've found an unstable slab.

    (1/22/2023) Wind transporting snow at sunset in the mountains above Smiley Creek.

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. 

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