Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Low-density snow and steady strong to extreme wind will create dangerous wind drifts in steep, exposed, upper and middle elevation terrain. This added snow load will also stress buried weak layers, making large avalanches more likely today. Your odds of triggering an avalanche are higher in the western portion of this zone (Dollarhide Summit to the Soldier Mountains) than in the mountains near Ketchum and Carey. You can reduce the chances of getting caught in an avalanche by sticking to slopes more sheltered from the wind.

Avalanche problems

  • Persistent Slabs

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

    Layers of weak snow can be found throughout the snowpack:

    • Periods of sun, warm temperatures, and rain created a variable mix of crusts and facets near the snow surface. These crust + facet layers may produce smaller but touchy slab avalanches as snow accumulates.
    • 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.
    • 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.

    Ben found ugly snowpack structure and poor snowpack test scores near Dollarhide Summit (observation, photos) and in Adams Gulch (observation) 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
    Likely
    Size
    1–2

    The Soldiers and mountains near Dollarhide Summit should pick up 8-10" of new snow by 5 PM, adding to last night's 2-6". This storm is producing low-density snowfall of about 4-5%.  Wind will blow strong to extreme from the W and NW, and it won't take much wind to get this snow moving. Expect whiteout conditions at upper elevations and any middle elevation terrain exposed to the wind. 

    Expect to find a variety of stiff and hard wind slabs in exposed terrain. Yesterday I found thin wind slabs sitting atop a temperature crust that formed Monday; these may be particularly touchy today. 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 wind-loading also adds 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

It's probably going to be pretty nasty out there today. With low-density snowfall, it won't take much wind to create whiteout conditions. Today's a good day not to bite off more than you can chew. Conditions will worsen throughout the day as steady wind and snow build fresh slabs on most slopes exposed to the wind. 

Wind slabs are likely to be touchy. We've had a grab-bag of weather this week including rain Monday afternoon, snow and strong wind Tuesday, sun, light snow, and graupel Wednesday, and clear, cold nights. This mix of weather created a smorgasbord of snow surfaces that will sit beneath today's snow.

I'd expect the majority of the small avalanches we see today to 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.

Larger avalanches, failing on weak layers deeper in the snowpack, are also more likely today. I think it's important to remember that many of our northern and western mountains have seen nearly continuous snowfall in the last two weeks. Sure, there have been a few lulls, but, as far as our persistent weak layers are concerned, I see this storm more as a culmination of a much longer loading event. As a complex picture becomes even murkier, I'd urge you to take a big step back in your terrain choices and avoid all steep, wind-loaded terrain. 

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