Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering an avalanche is most likely where the recent snowfall and wind have formed drifts. The avalanche danger may be greatest in the Soldier Mountains, where large triggered avalanches occurred yesterday and Thursday. Weak layers exist in the top several feet of the snowpack—while less likely, avalanches are also possible in areas sheltered from the wind. You may be able to trigger slides remotely: from flatter terrain above, below, or to the side of a steep slope. With warming temperatures today, wet sluffs will become possible—primarily at lower elevations.

If you're traveling in the upper reaches of the Warm Springs Ck drainage near Dollarhide Summit where more snow fell this week, refer to the Galena Summit & Eastern Mtns zone forecast. 

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Avalanche problems

  • Persistent Slabs

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

    Yesterday, sledders in the Soldier Mountains remotely-triggered a persistent slab avalanche from the base of the slope (photo above/right). In the Wood River Valley, the February drought left a very weak snowpack, and a concentrated avalanche cycle took place when this snowpack was loaded. Given the recent loading from new and wind-transported snow, triggering a persistent slab avalanche on these weak layers remains possible. Avalanches are more likely on recently wind-loaded slopes, but they could occur on slopes that are sheltered from the wind as well. 

    These unstable layers don't exist everywhere, which makes them more insidious, difficult to manage, and more likely to catch you by surprise. You are most likely to find them on slopes that face E-NE-N-NW. On these aspects, it's best to assume these layers exist and choose lower angled terrain not threatened by steeper slopes above. Remember that persistent slab avalanches can be triggered remotely—from flatter terrain above, below, and to the sides of avalanche starting zones. 

  • Wind Slabs

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

    On Thursday above the Soldier Mountain Ski Area, a snowmobiler triggered a large wind slab avalanche but fortunately was able to ride out of it (photos in Media section below). The hard wind slab broke 2-3 feet thick and pulled into very gentle terrain at the ridge crest. It's possible this slide may have involved the persistent weak layers described above.

    Increasing winds overnight—especially in the Soldiers—may have produced a fresh round of wind drifts. Use snow surface textures (like ripples and dune-like drifts) to help you identify wind-affected areas from a distance. When you find a wind slab, expect the snow to be thicker and denser than snow that is unaffected by the wind. Cracks shooting out from your skis, board, or machine are a great sign that you've found a sensitive wind slab.

    ADDITIONAL DISCUSSIONWarmer temperatures today could lead to wet snow slides, sluffs, and "dribbles". This will be most likely on shady aspects (NE-N-NW) at lower elevations. If the sun stays out longer than forecast today, the wet snow problem could creep into middle and upper elevations.

Avalanche Discussion

What's old is new again. After dealing with widespread persistent weak layers for the first part of the winter, an extremely dry February left us with a stable snowpack and LOW danger by March. But now persistent slabs are back on the problem list—déjà vu anyone?

Many folks think of weak, faceted snow as an early-season phenomenon, but the clear nights and temperature swings of spring can be perfect for forming facet layers at the surface of the snowpack. Often times, these facet layers are mixed in with crusts formed by the sun and warming. During the first half of March, an alternating pattern of small spring storms and clear, cold weather created several of these weak layers. More consistent snowfall in the second half of March has now buried these persistent weak layers beneath 1.5-3+ feet thick slab.  

These persistent weak layers exist throughout the forecast area, but seem to be most common and reactive in the Galena Summit area, the Smoky Mountains (including the Western Smokys and Salmon Headwaters), and the Soldiers. In these areas, there have been four, possibly five, human-triggered persistent slab avalanches since late-March. A number of natural and earthquake-triggered avalanches in recent days appeared to break down to these layers as well. Snowpack observations from our northern mountains have been sparse, but these weak layers may be less common in the Sawtooths and the Banner Summit area—but I wouldn't rule them out.  In the Wood River Valley, there has been less recent loading on these weak layers.

Spring persistent slab problems make me nervous, especially when they follow an extended period of relative stability like we experienced in late-February into early-March. We all seem to understand that these problems are "normal" during the early winter, and we get in the habit of choosing mellow terrain. But by spring, we expect a more stable snowpack and smaller, more manageable avalanche problems. Quite often that's the case—but not always. In fact, our area has had two avalanche fatalities in April, one major injury in late-March, and a number of late-season close calls.

This isn't a typical spring, not on a global scale and not on the scale of our snowpack. There are a number of reasons to ratchet it back out there—and triggering a dangerous persistent slab avalanche is one of them.

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