Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions exist. The combination of intense snowfall and wind has created wind slabs that will be large and easy to trigger. This additional load is also adding weight to older weak layers, buried 1-3 feet deep in the snowpack. Human-triggered and natural avalanches are likely — travel in avalanche terrain is not recommended.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2

    Over two feet of low density new snow has fallen in favorable portions of this zone. Much of this snow was transported into slabs yesterday as wind speeds increased. Another round of snowfall overnight made for additional ammunition for the winds. As you gain elevation, you will be more and more likely to find these slabs and they will grow in thickness and distribution. They will be most largest and most sensitive in upper elevation terrain where winds are strongest and are transporting the most snow.

    Several observers in the Soldier Mountains reported avalanches that failed in heavily wind loaded areas sometime Sunday night or early Monday morning. Natural wind slabs failed during the same time frame in the mountains above the Wood River Valley (photo at right). Over the weekend, I was up high in the Boulder and Smoky Mountains. I watched as the wind quickly built slabs out of the fresh, low density snow, erasing my skin track in minutes (video here). On both days, I found that these slabs were sensitive to my weight (photo here) and I avoided entering avalanche terrain.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3

    Buried weak layers in the snowpack are being pushed towards their breaking points. An ongoing storm has loaded the snowpack with 1-2’ of snow in the past 4 days and it is struggling to accommodate that load. Yesterday, in the mountains near Hailey, Scott observed cracking and slumping on a slope that wasn’t quite steep enough to slide (photo at right). 

    These weak layers are widespread, but are most sensitive to triggering where winds have added extra weight to a slope. I found this exact combination yesterday in the White Cloud Mountains (photo here, video here) and it is where you will be most likely to encounter one of these beasts today. However, even in the absence of wind loading these layers may be sensitive to your weight, thanks to the amount of recent snowfall. Avalanches failing on persistent weak layers can break wider than you expect, spanning terrain features that typically confine wind slab avalanches. These slides may be triggered remotely — from gentle terrain connected to adjacent steeper terrain.

Avalanche Discussion

After issuing yesterday’s forecast I headed to the White Cloud Mountains. I visited a location that I’d been to 10 days prior for a simple reason: I wanted to see how a snowpack I was familiar with was dealing with the new snow. On my last visit I experienced a few isolated collapses and got unstable snowpack test scores, but determined that we were in the proverbial “weak snow without a slab” situation. I wanted to know if the ongoing storm was providing the missing component to that equation.

As I walked through low angle terrain not threatened by avalanche hazard, my question was quickly answered. I traveled a nearly identical path as on my last visit and I experienced almost continual collapsing of the snowpack. Heraclitus taught that a man can never set foot in the same river twice; I suspect he would have felt the same about a snowpack.

When the snowpack collapses you are missing one key ingredient for an avalanche — a steep slope. After experiencing widespread collapsing down low, I continued upwards, hoping to see some steeper terrain and look for evidence of natural avalanche activity. As I crested a ridgeline, I looked into the steeper bowl on the other side and found exactly that. A large cornice had collapsed, triggering an avalanche that failed on old, weak snow just above the ground. The slide broke several hundred feet wide and wiped out the majority of the seasons snowpack. 

Avalanche forecasting and safe backcountry travel are complex art forms. I like to think about both activities as ongoing, iterative processes. Before I leave my house in the morning I have a picture in my head of what I expect to find in the backcountry. As I travel through the mountains I make observations and add them to my mental model. The picture in my head is continually being updated as the weather changes and as new information becomes available. The “river” we are walking in is never the same, and neither are we.

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