Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

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Limite del bosco
1 · Debole
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In sintesi

You're most likely to trigger avalanches where the wind recently formed drifts or slabs. On shady slopes that are more protected from the wind, triggering a 1-2 foot thick avalanche is not out of the question. Consider the consequence of a slide before committing to avalanche terrain. Even small slides can have bad outcomes on slopes with cliffs, trees, and terrain traps.

Problemi valanghivi

  • Persistent Slabs

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

    Multiple weak layers exist in the snowpack, and triggering a persistent slab avalanche remains possible. The distribution, sensitivity, and depth of these layers vary across the zone. Here are two distinct scenarios:

    1. Surface hoar: A skier triggered a slide near Galena Summit Sunday (view report). The 1-2' thick avalanche failed on a layer of buried surface hoar. This layer is responsible for several skier and rider triggered avalanches since mid-January. This layer is most problematic on slopes facing NW-N-NE that are steeper than about 35 degrees. You're most likely to encounter this problem in the Soldier Mtns and near Dollarhide Summit. In the Wood River Valley mountains, most slopes lack a slab above this weak layer. 
    2. Older weak layers: Crusts and/or facets, and occasionally surface hoar, exist deeper in the snowpack. These are buried beneath dense, 2-4' thick slabs—making them difficult to trigger but capable of producing very dangerous avalanches. While triggering them is unlikely, it can't be ruled out in rocky, wind-affected, alpine terrain (photo above/right). Slopes like these have variable snow depths, with thinner areas of the snowpack that allow us to impact deeper weak layers.

    Overlapping, variable weak layers make avalanche conditions hard to predict. The single best way to reduce your risk is by avoiding slopes greater than about 35 degrees. 

    (1/24/2023) This recent large avalanche occurred on the shoulder of Duncan Ridge in the Pioneer Mountains. It appears to be a heavily wind-loaded slope that broke on a persistent weak layer. A smaller wind slab avalanche is visible further right in the image. 10,100', WSW.

  • Wind Slabs

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

    Recent NW-N-NE wind formed soft and hard slabs in exposed terrain. A handful of small natural wind slab avalanches occurred over the weekend (Galena Pass, Banner). Monday, we spotted a large wind slab in the Soldier Mtns (photo). 

    This problem is most dangerous at upper elevations where slabs are larger and more widespread. Look for them near ridgelines, on the sides of gullies and chutes, and near prominent terrain features. 

    Cracks shooting out from your skis or sled are an obvious sign of instability (example). Watch for drifts, dunes, and ripples on the snow surface. Older hard slabs can have a smooth, chalky appearance and feel and sound hollow, like a drum. Wind-deposited snow will be stiffer and keep your skis or snowmobile closer to the surface.

    (1/30/2023) This large avalanche in the N Fork Soldier Ck drainage released on a SE aspect near 9000', likely over the Jan 28-29 weekend.

Avalanche Discussion

EAST VS WEST

Avalanche conditions vary across this zone. The primary factors behind this difference are snow depth and a relative lack of recent impactful weather in the mountains surrounding the Wood River Valley.

  • East: On the eastern side of this zone and in the mountains above the Wood River Valley, the snowpack remains thin (around 3 feet deep); much of the snowpack is faceting. In the past week, we've seen a few "facetlanches," dry loose snow avalanches involving old, weak faceted snow at the surface instead of the more typical "powder" dry loose avalanches. As the entire snowpack facets, both weak layers and slabs are losing strength. With the decrease in slab stiffness, triggering slab avalanches becomes more difficult. Here, you are much more likely to trigger a slide where recent winds have built slabs on top of the weak, shallow snowpack.
  • West: On the western side of this zone (Dollarhide Summit and west to the Soldiers), the snowpack is 4-6 feet deep, and the slabs above the weak layers remain intact (video). The persistent weak layer (facets or surface hoar) buried in early January lies beneath a 1.5-2 foot thick slab. While recent snowpack tests indicate that this layer is stabilizing, I'm not ready to ignore the chance of triggering a slide on wind-protected, shaded slopes where this layer is at its worst. Weak layers buried in November and December lie beneath very dense, heavy slabs of snow. Impacting these weak layers is less likely.A few generations of wind slabs formed in the past week. The most recently formed slabs are small and softer but may be more reactive to your weight. Warm mountain-top temperatures have helped this problem heal, but I'd keep it on your radar if you plan to ski or ride wind-exposed terrain. Triggered wind slabs can be effective triggers for deeper weak layers in the snowpack.

The consequences of triggering avalanches can vary significantly. Triggering a small slide in terrain free of rocks, trees, and terrain traps is much less dangerous than triggering a slide in extreme, rocky, treed terrain with a terrain trap at the bottom. Think about the consequences of being caught in a slide before committing to skiing or riding in sizeable avalanche paths. 

 In case you missed it, check out the latest Weekend Update here.

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