Avalanche forecast

Soldier & Wood River Valley Mtns

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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering a large avalanche remains possible in the eastern portion of this zone (the Little Wood drainage, southern Wood River Valley, Pioneer Mtns, and near Bald Mtn). In these areas, 16-20 inches of recent snow fell on a very weak snowpack. Avalanches can be triggered remotely—from a distance below, above, and to the side of steeper slopes. Avalanches are most likely in areas with recent wind loading but are possible in sheltered terrain as well. Wind and new snow are building thin, fresh drifts in upper elevation terrain that may be sensitive to your weight. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Thanks to significantly below-average precipitation and a prolonged drought in February, a very thin and very weak snowpack exists in much of this zone. Beginning last weekend, 16-20" of new snow fell on this weak snowpack, resulting in a large amount of natural avalanche activity (photo at right). As the days without additional snowfall pass, the likelihood of triggering a slide on this weak snow decreases, but this process is happening very slowly. On Sunday, as I traveled in the East Fork of the Big Wood, the snowpack collapsed underneath me in a number of places and my snowpit tests yielded unstable results. That same day, an observer on Patterson in the mountains east of Hailey reported triggering collapses that traveled hundreds of feet. They stuck to low angle terrain to manage their exposure to this problem. 

    Persistent slab avalanches can fail in ways that catch even experienced backcountry users by surprise. You may be able to trigger slides remotely: from flatter terrain above, below, or to the side of a steep slope. Choosing lower angled terrain not threatened by steeper terrain above is the only way to safely "manage" this problem. 

    ADDITIONAL DISCUSSIONBy the end of the day, 1-3 inches of snow will have accumulated in portions of this zone. Moderate to strong gusty winds are building slabs with this new snow. Any slabs that form will remain small, but even a small slab can knock you off your feet and drag you through high-consequence terrain. 

Avalanche Discussion

In all aspects of life, we sort the world into boxes to help us understand and communicate about the reality we encounter.  As avalanche forecasters, we use boxes known as avalanche problems to help describe the type of unstable snow that you might encounter in the backcountry. Different problems form in different areas and require different management strategies in order to avoid the hazard they pose. The avalanche danger is MODERATE in all of our zones today, but the avalanche problems and the hazard mitigation strategies are very different. 

In our northern areas, we are primarily dealing with a WIND SLAB problem right now. Avoiding the danger posed by a wind slab is relatively simple. (Notice the word "relatively" in there, I didn't just throw that in for fun. The backcountry environment is an incredibly complex one and we are well served to give it the respect it demands.) We can avoid wind slabs by avoiding terrain that is affected by the wind. No wind, no wind slab. If we want to cut things a bit closer, we can travel in terrain that is exposed to the wind, but where the wind has removed snow (scouring) instead of adding snow (loading). If we choose to cut our margins even closer, we can travel in terrain where the wind has been loading slopes with slabs and attempt to assess the stability of the wind slabs. Being able to do this successfully requires a great amount of experience and opens you up to high consequences if your assessment goes awry. 

In the southeastern portion of our advisory area, we are currently dealing with a PERSISTENT SLAB problem. Persistent slabs are an entirely different beast to deal with than wind slabs. They form when weak, long-lived (hence "persistent") layers of snow are buried. As you just read, there are several options available when it comes to managing a wind slab problem. In contrast, a persistent slab problem presents a problem with few management strategies. Most of the time, the only real option you have is to avoid the terrain where the problem exists. I've spent many, many days in the backcountry, digging hundreds of snowpits and assessing snowpack stability. But even though the danger is "only" moderate in the Soldier and Wood River Valey zone right now, there are many places that I wouldn't even think of venturing.  

Still with me here? When things are simple, the types of avalanche problems that you encounter in the backcountry feat neatly into the avalanche boxes. However, if you're old enough to be reading and understanding an avalanche forecast you probably know that the world we live in is rarely simple. The month of March has been dominated by alternating periods of snowfall and clear weather. Between storms, weak layers of snow formed at the snow surface and were subsequently buried by the next round of snowfall. In areas where wind slabs have formed on top of these weak layers, the wind slabs are adding additional stress to the weak snow underneath.

Is this a wind slab problem or a persistent slab problem? I suspect you all have some extra free time today. I'd like to challenge you to spend some time thinking about what type of problem you might think of this as and how you might manage it. Call your favorite backcountry partner and ask them what they think. Today is a great day to open up your brain and learn something new. The backcountry environment always challenges us and provides us with endless opportunities to learn something new. Clear your brain of your preconceived notions and make an effort to look at this idea with fresh eyes. I promise it is worth your time and effort. After all, those who think they know never learn.

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