Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The combination of new snow and strong winds is building sensitive wind drifts and loading buried weak layers, particularly in the western portion of this zone (Dollarhide Summit to the Soldier Mountains). Triggering an avalanche 1-3 feet deep is 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.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

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

    1. Depth hoar exists near the ground on all aspects (excepting low elevation slopes that are snow-free). This is the snow that we've been talking about all season long and seem to be destined to talk about for the remainder of the season.
    2. In the middle of the snowpack are several interfaces that have produced both avalanches and unstable test results in recent days. In this zone, these layers appear to be worst where they are accompanied by a crust.

    I went looking for these problems in this zone on Sunday and I found them. Near Dollarhide summit, I dug snowpits on shaded slopes and those that face the sun and got poor snowpack test results in both locations. You can read my observation here, and see a photo of those snowpits here. As I continued upwards, I found a large, natural avalanche that appeared to have failed on a crust before stepping down to weak snow near the ground within the last few days. This slide was located in exactly the type of terrain that you should be avoiding if you want to reduce your risk of encountering a slide today: wind-affected slopes steeper than about 35 degrees. You can greatly reduce your risk of triggering a large persistent slab avalanche by sticking to 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

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Strong winds blowing overnight built wind slabs in exposed middle and upper elevation terrain. While only an inch or two of snow fell, the wind has been blowing hard enough that it is likely finding older pockets of unconsolidated snow to throw around as well. Sunday, near Dollarhide Summit, I watched the wind moving plenty of snow and encountered recent thin, stiff drifts as I climbed in elevation. On Saturday, Soldier Mountain Cat Ski guides remotely-triggered a wind slab avalanche that broke 1.5' deep (photo above/right).

    Triggering an avalanche such as the one pictured will be a real possibility today. Wind slabs may be found both near ridgelines and near mid-slope terrain features such as ribs and gullies. These slabs are hazardous in their own right but they are also adding stress to the weak layers buried in the snowpack (described above). Any wind slab you trigger could step down to these deeper layers, producing a much larger and more dangerous avalanche. 

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

Avalanche Discussion

A DAY OF CHANGE

The past 24 hours were a transitional period for the snowpack. Over the previous 10 days, a steady trickle of snow gradually accumulated in much of our area. If you live in the Wood River Valley, this may be hard to believe, but I assure you it is true. Throughout this period, winds remained relatively light and temperatures were cool. That sounds like a perfect recipe for good skiing and riding conditions to me. Unfortunately, conditions changed significantly yesterday. Valley bottom temperatures climbed into the low 40s F and many ridgeline locations approached freezing (32F). In the afternoon, light rain was observed in several locations in the mountains north and west of Galea Summit. In addition, the wind speed increased dramatically overnight, with average speeds in the mid 20s and gusts above 50 MPH.

These three meteorologic events (warm temperatures, rain, and wind) mean that the snowpack you encounter today is different from what you might have found this weekend. Warm temperatures promote settling of the snowpack, which can add some heft to the slab of snow sitting on top of our buried weak layers. In addition, these warm temperatures combined with a dose of sun and some spits of rain introduced another crust to the snowpack in many areas. Crusts can form long-lasting weak layers in the snowpack if they are accompanied by facets (find a short video about this here). To top it all off, wind speeds increased significantly overnight. When strong winds blow they can work their way into areas that are generally sheltered, picking up the soft snow that has been hiding out there and building fresh slabs with it. As you head into the backcountry today, be alert to all of these changes within the snowpack. Its a new world every day out there. 

 

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