Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
1 · Low
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Out of date — this forecast expired 6 years ago.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

It's becoming less likely, but 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, weak snow is buried beneath a 1-2 foot thick slab. Avalanches are more likely where recent wind drifts exist, but are possible on sheltered slopes as well. Avalanches can be triggered remotely—from flatter terrain below, above, or to the side of steeper slopes. 

Avalanche problems

  • Persistent Slabs

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

    February's drought left a very thin and weak snowpack in much of this zone. In the middle of March, a pair of storms brought 1.5 to 2 feet of snow to the southeastern portion of this zone. This snowfall produced a concentrated avalanche cycle, with many slides breaking hundreds of feet wide (photo at right/above). In the time since, these slabs have become less reactive, but the lingering possibility of triggering an avalanche on this weak snow remains. On Friday, I went skiing in the Eagle Creek drainage, at the northeast corner of this forecast zone. Much less snow fell in this area in the past two weeks, so the overlying slab was thinner, but I still got some collapsing of the snowpack where the wind had built a thicker slab. While these avalanches are most likely on recently wind-loaded slopes, they can occur on slopes with no recent wind-drifting as well. 

    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. While these avalanches are most likely on recently wind-loaded slopes, they can occur on slopes with no recent wind-drifting as well. 

Avalanche Discussion

The month of March has been marked by unsettled spring weather. Much of our forecast area received measurable amounts of precipitation on 9 of the past 28 days. In between these stormy days we've seen patchwork skies with a mixture of sun and clouds depending on your location. Let's take a minute to think about how this affects the snowpack:

Intense spring sunshine can quickly melt fresh snow. After this wet snow refreezes, this process tends to result in a strengthening of the snowpack. Simple enough. However, when the sun starts to melt the snow but clouds put a halt to the process something else happens. A thinner, more fragile crust is left behind in this case, often accompanied by some small, angular snow crystals known as facets. Periods of storms followed by periods of partly cloudy skies left behind layers of crusts and facets that are buried in the snowpack. Today, with more fresh snow on the way, we will bury another set of these layers.

The tricky thing is that these layers have proven to be variably reactive. Why is that? Our forecast area spans quite a large chunk of terrain, over 3000 square miles. On any given day, the weather varies significantly across this area. Passing clouds might provide some cover for one mountain while the sun is shining brightly on a neighboring mountain. But the weather isn't the only important factor in this equation. The direction a slope faces and the steepness of the slope both affect how much incoming solar radiation hits the slope. Because of these factors, the character of the weak layers that are buried in the upper portion of the snowpack varies from slope to slope. In many areas, the bonds at these interfaces are strong enough to support the slab on top of them, but in some they are not. Skiers in the Smoky Mountains encountered one of these weaker areas yesterday when they triggered an avalanche on a sheltered, north-facing slope. Be on the lookout for this problem, particularly in areas where the wind has built stiffer slabs on top of these weak layers. 

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