Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You can trigger large avalanches that fail near the ground and involve the entire snowpack. You likely will not see any warning signs such as cracking and collapsing. Slides can be triggered after other skiers and riders cross a slope. Newly deposited pockets of wind-drifted snow will be reactive to your body weight. If triggered, these pockets can "step-down" to make larger avalanches.

Conditions are more dangerous in the western half of this zone —from roughly Dollarhide Summit and west into the Soldier Mtns and the South Fk of the Boise River drainage.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Weak snow exists near the base of the snowpack on many slopes. This weak layer may makeup the whole snowpack on some slopes, or live below a firmer slab on others. This weak snow is at its worst on upper-elevation slopes, as well as NE-N-NW aspect mid-elevation slopes. On shaded slopes, you'll find obvious weak snow if you dig a quick hand pit into the snowpack. On more solar aspects, you'll find a harder-to-identify layer of small facets on top of a sun crust. 

    Recent snowfall and wind slabs are adding stress to this weak snow, making it easier to trigger a slide. You are most likely to trigger avalanches on slopes that have wind deposits, or wind slabs, on the surface that can "step down" to deeper weak layers. Areas that have varying snowpack depths due to wind loading and shallow rocky sections are the most likely trigger points for this weak layer. Don't expect any warning signs such as cracking and collapsing before triggering this problem. 

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    With 2-6 inches of cold, dry new snow falling with sustained moderate winds, wind-affected snow is a certainty in the mountains. Exposed areas near ridgelines and confined cross-loaded terrain features such as gullies are where you are most likely to encounter these avalanches. Cracks shooting out from your skis or machine are a clear indication that you've found an unstable slab. Look for these slabs in exposed upper-elevation terrain, where the wind is slowed down and forced to drop the snow that it is carrying. In the steep, rocky terrain of the Sawtooths, slabs also commonly form below large cliff bands and on the aprons below couloirs. 

    While these will be relatively small in size today, expect these near-surface, shallow problems to entrain weak snow lingering below if triggered. Given the amount of weak snow in our underlying snowpack, smaller slides that might normally have low consequences on their own are likely to have larger consequences today. An observer reported triggering an unexpected loose dry facet-lanche yesterday near Galena Pass (see photo at right, observation). This weak snow instability is what can be triggered with wind slabs today. 

    (1/7/2024)

    This loose, dry facet-lanche was triggered near the Grand Prize trailhead on an NW aspect. It began as sluff from initial turns and grew as it moved downhill. 

    The avalanche traveled a 1/4 mile and dropped 800 vertical feet creating a noticeable powder cloud that shook trees in the runout. Slides like these can easily knock you off of your feet and bury you in a terrain trap, and are likely to be triggered below new wind slabs.

    Photo: Sam Linnet

Avalanche Discussion

As storms bring more snowfall to our area, the snowpack loses stability and gains complexity. In the past three days, moderate to strong shifting winds accompanied 1-6 inches of cold, dry, new snow. We've been focused on the weak layer near the base of the snowpack for most of the season, but now we've added a new flavor of avalanche to the mix.

Rounding out our three-week drought, the snowpack is entering a new storm cycle with some damage. Weak snow is left both at the base, around crusts in the middle, and in some locations makes up the entire snowpack itself. Snow surfaces prior to our snowfall harbored widespread, well-developed surface hoar. While which of these you may find will vary depending on aspect and elevation, weak snow exists in most locations. Where you're finding a slab above this, you'll find the recipe for avalanches. New snowfall and wind have built slabs on top of weak surfaces. Near-surface instabilities are likely to be rather small on their own, but will be reactive to your body weight. However, these are not separable from what lies below. 

What happens on the surface affects what lies underneath. The near-surface instabilities like these wind slabs or sluffs of soft new snow sit atop an already weak snowpack. What may typically be a smaller wind slab may entrain the weak, unconsolidated snow underneath if triggered and produce larger slides than anticipated (view observation). While the persistent slab problem has been becoming less reactive, these near-surface instabilities have the potential to step down and create a large, destructive persistent slab avalanche. As you head out into the mountains, be sure to not only evaluate what is above, but also what is below. 

As conditions change and complexity increases, we find ourselves stepping back from the terrain we've been playing in recently. This process is started yesterday and will continue over the coming days as active, wintery weather continues to impact our region. We are all hungry for powder, but I encourage you to take the time to clear your head and think about the avalanche problems that exist in the terrain you are planning on visiting today. 

Regioni coperte