Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Recent strong winds transported snowfall from the past week, forming fresh, stiff wind drifts and stressing buried weak layers. The size and chance of triggering avalanches are higher in the western portion of this zone (Dollarhide Summit to the Soldier Mountains) than in the mountains near Ketchum and Carey. Triggering an avalanche 1-3 feet deep remains possible, especially on steep, upper elevation slopes. You can dramatically reduce your risk of getting caught in an avalanche by sticking to terrain that is sheltered from the wind.

Avalanche problems

  • Persistent Slabs

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

    Layers of weak snow can be found near the ground and in the middle and upper portions of the snowpack:

    1. Depth hoar exists near the ground on all aspects that hold snow. This is the weak snow that we've been talking about all season long and seem destined to talk about for the remainder of the season.
    2. In the middle of the snowpack, several interfaces have produced both avalanches and unstable test results in recent days. These layers appear to be problematic where accompanied by a crust.

    Ben found ugly snowpack structure and poor snowpack test scores near Dollarhide Summit (observation, photos) and in Adams Gulch in recent days.  He also found a large, natural avalanche that appeared to have failed on a crust before stepping down to weak snow near the ground.

    You can greatly reduce your risk of triggering a large persistent slab avalanche by playing on slopes less than 35 degrees that are sheltered from the wind.

    (2/12/2021) This avalanche was triggered by a rider NE of Wells Summit in the Soldier & Wood River Valley zone. The slide broke around 40' wide and carried the rider about 100 yards. A section of the cornice also released in the slide.

  • Wind Slabs

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

    Over the weekend, Soldier Mountain Cat Ski guides remotely-triggered a wind slab avalanche that broke 1.5' deep (photo above/right). Since then, strong to extreme winds have moved literally tons of snow at middle and upper elevations.

    Expect to find a variety of stiff and hard wind slabs in exposed terrain. While hard slabs support your and your sled's weight, they fail unpredictably when stressed to the breaking point. Hard slabs can break well above you, pulling into flatter terrain near the ridgetops. 

    Be on the lookout for stiff snow that feels "punchy" or hollow underneath. You could find the recently formed wind slabs near ridges, on the sides of cross-loaded gullies, and lower on slopes near prominent terrain features. Recognize that the wind event also added stress to the weak layers buried deeper in the snowpack (described in Problem 1 above). Any wind slab you trigger could step down to these deeper layers, producing a much larger, more dangerous avalanche. 

    (2/20/2021) Ski guides remotely-triggered this wind slab avalanche on Peak 2 in the Soldiers while doing mitigation work. It broke 1.5' deep. Photo: Soldier Mountain Cat Ski.

Avalanche Discussion

TODAY'S SNOW SURFACE, TOMORROW'S WEAK LAYER

A storm will arrive today bringing snowfall to much of the western and northern reaches of the forecast area including Banner Summit, the Sawtooths, the Smokys, and the Soldiers. As the current snow surface is buried, it's a good idea to take stock of the interface that may prove to be our next problematic weak layer. 

We've had a grab-bag of weather this week including rain Monday afternoon, snow and strong wind Tuesday, sun, light snow, and graupel yesterday, and a clear, cold night last night. This mix of weather created a smorgasbord of snow surfaces that will sit beneath tomorrow's storm.

If I had to guess, the touchiest interfaces we'll see are those that involve facets above or below a crust (or two). Crusts exist on many slopes near or just below the snow surface. Warm ambient air temperatures Monday climbed into the low 40s F. Snow surfaces at low and middle elevations (both sunny and shaded) melted during the day and refroze overnight. The warm air also turned some snow showers to rain up to 9,000'. 

Crusts also formed on most steep slopes that face the sun, even at upper elevations. Check out this cool photo Scott took on Tuesday where you can see the sun reflecting off of a crust high on McDonald Peak in the southern Sawtooths.

Middle and upper elevation, shaded aspects are the areas most likely to be crust-free, but they don't necessarily get to duck out of the potential weak layer category. As skies cleared last night dry, very cold air likely promoted faceting in many areas. 

Throwing in recent wind effect and snowfall differences across the area I'd expect the patterns of weak layer distribution to be highly variable. Stability may change over short distances as you climb in elevation or wrap to different aspects. This storm will also add stress to known weak layers in the middle and at the base of the snowpack. As a complex picture becomes even murkier, plan to build a larger margin for error into your travel plans. 

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