Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You could trigger slab avalanches on slopes where the wind has formed drifts or stiffened the snow near the surface. These conditions are more common at upper elevations and become easier to spot and avoid as you drop in elevation. Even though it hasn’t snowed in a while, there’s a chance you could trigger slides remotely — from gentle terrain above, below, or to the sides of steeper slopes.

Avalanche problems

  • Persistent Slabs

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

    Terrain with both a buried persistent weak layer (surface hoar or sugary facets — many upper elevation and some middle elevation slopes — and recent wind-loading or wind-stiffened snow at the surface — some upper elevation and isolated middle elevation slopes — are capable of producing slab avalanches. In this Zone, we have the weak layer but, generally speaking, are missing the wind-loading (slab) part of the equation.

    Wind-loaded slopes are more common in the Soldier Mtns than in the Wood River Valley Mtns, so the chances of finding trouble are higher as you move west in this zone. On Friday, riders in the Soldiers found the right combination of weak snow and wind when they remotely triggered a small avalanche on a wind-affected slope (see photo). Yesterday, the Sun Valley Ski Patrol intentionally released a sizeable slab avalanche on a north aspect while checking a closed area before opening the resort. The slide failed on weak, faceted snow low in the snowpack but was an outlier in that the slab was man-made; snowmaking guns aimed at the starting zone loaded the slope with a dense slab with some ice layers in it. This event is a good indicator of what we can expect to see in the Wood River Valley mountains when mother nature turns on the natural snowmaking machine. 

    ]If you experience red flags (collapsing and cracking) or just want to minimize the chance you'll trigger a slide, avoid wind-loaded slopes and/or stick to gentle terrain. If the snow surface isn't "blower powder", you're on a wind-affected slope. Triggering avalanches remotely — from gentler terrain above, below, or to the sides of steeper slopes — remains a possibility. Learn more about our snowpack and these weak layers in the Forecast Discussion section below.  

Avalanche Discussion

We need three ingredients to have an avalanche: a weak layer, a slab, and a slope. 

  1. The weak layer: We have persistent weak layers, in spades. We buried a widespread layer of surface hoar in early December and have seen extensive avalanching following each storm since then. We’ve found these weak, feathery crystals buried from Banner Summit, down through the Sawtooths and Western Smokys, across the valley into the White Clouds, south to Galena Pass, further south into the Boulders, and in the mountains east of Ketchum and Hailey. The avalanche near Miller Creek in the Soldiers likely involved this layer too. In short, we’ve found it almost everywhere we’ve been. The nature of the snowpack varies widely across our forecast zones, but this layer is an ugly constant. The surface hoar is most widespread on shady and partially shady aspects, but we have seen it regularly on sunny aspects too. We also have a depth hoar issue in the northern and western mountains, areas that harbor lingering snow from September and October storms. Many upper elevation and shady middle elevation slopes have both of these weak layers. Ouch.
  2. The slab: The northern and western Zones received a healthy dose of snow and wind with the last storm, forming widespread slabs. The Wood River Valley did not receive as much snow, so slabs (and avalanche activity) were not as widespread.
  3. The slope: This is what you control. You can assume as much or as little risk as you want; it’s your choice. Where you have both a slab (wind-loaded terrain) and a persistent weak layer (most upper elevation and many middle elevation slopes), playing it safe by avoiding avalanche terrain is prudent. Sorry to be the bearer of bad news.  

Going forward: The widespread buried surface hoar problem is a rare occurrence in this area, meaning none of us have a lot of experience dealing with it. We don’t have the “personal databases” to be able to accurately predict how individual slopes will behave when we load them during small to medium-sized storms in the coming weeks. Avalanche forecasting — and playing in avalanche terrain — is all about minimizing uncertainty, and there’s a lot of uncertainty on the horizon. Buckle up for a bumpy road ahead. 

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