Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Triggering a large avalanche remains a possibility—primarily in wind-affected terrain. In these areas, a dense slab may exist atop a variety of buried weak layers. To reduce your risk, avoid slopes with evidence of wind such as fresh drifts or a stiffer snow surface that supports your skis or sled.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    Several persistent weak layers exist in the snowpack. On the plus side, the lack of significant recent loading is allowing these to improve. But on the negative, the variability and complexity of the snowpack make conditions less predictable.

    • A layer of surface hoar is buried 1-1.5' deep on many shady (E-N-W) slopes. While this layer seems to be less common in this zone—especially in the mountains around Ketchum and Hailey—it was likely responsible for at least one triggered slide last week in the Soldiers (details). The surface hoar is most problematic where recent or past wind loading had created a stiffer slab in the upper snowpack.
    • Older weak layers consisting of crusts and/or facets exist deeper in the snowpack. These are buried beneath dense, 2-4+ thick slabs—making them difficult to trigger but capable of producing very dangerous avalanches. While triggering them is unlikely, it can't be ruled out in rocky, wind-affected alpine terrain. Slopes like these have variable snow depths, with thinner areas of the snowpack that allow us to impact deeper weak layers. 

    While there are nuances with each of these, there are common themes. You are more likely to trigger an avalanche on very steep slopes (greater than about 35 degrees) where the wind has influenced the snowpack. You can recognize wind-affected areas by stiffer snow that is more supportive of your skis or machine and surface texture such as ripples, waves, or dunes.

    (1/24/2023) This recent large avalanche occurred on the shoulder of Duncan Ridge in the Pioneer Mountains. It appears to be a heavily wind-loaded slope that broke on a persistent weak layer. A smaller wind slab avalanche is visible further right in the image. 10,100', WSW.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    The ongoing wind event continued yesterday and overnight. Northerly winds tend to be particularly localized and variable in our area, and weather stations often underreport them. The wind in the Soldiers blew at strong to extreme speeds, as it often does when the wind comes from the N-NW.  The wind atop Baldy increased into the moderate to strong range yesterday afternoon. Scott was in Baker Cr yesterday and reported strong N winds and snow plumes off nearby ridgelines.

    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. Scott encountered a few hard wind slabs yesterday and was able to get one to crack out 20 feet from his skis. Ben observed a small, fresh wind slab avalanche in Hyndman Creek (photo). 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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