Avalanche forecast

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Avalanche danger

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

You're most likely to trigger avalanches where the wind recently formed drifts or slabs. In areas more protected from the wind,  triggering a 1-2 foot thick avalanche is not out of the question on shady slopes facing E-N-W. Pay attention to the consequences of being caught in even small slides in terrain with rocks, cliffs, trees, and terrain traps.

Avalanche problems

  • Wind Slabs

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

    What is it?  Last week's NW-N-NE winds formed 1-3 foot thick, hard and soft wind slabs in exposed terrain. Over the weekend, light snowfall and continued northerly winds formed a thinner, softer generation of wind slabs. Monday, we spotted a large, fairly recent wind slab avalanche in the Soldier Mtns (photo to right/above). While the wind slabs are becoming more difficult to trigger with each passing day, observers report widespread wind-affected snow surfaces throughout the forecast area. Reports of snowpack cracking are decreasing, but professionals continue to steer clear of recently formed wind slabs.

    Where is it?  Wind slabs are largest and most widespread near exposed ridges. You may find them near ridgelines, on the sides of gullies and chutes, and near prominent terrain features. Wind slabs are larger and more widespread in the western half of this zone.

    How can you recognize it?  Cracks shooting out from your skis or sled are an obvious sign of instability. Watch for drifts, dunes, and ripples on the snow surface. Wind 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.       

    How can you manage it?  The easy move is to avoid obviously wind-loaded avalanche terrain. Hard slab avalanches can behave unpredictably, breaking above skiers and riders. Any triggered wind slab could "step-down" to buried persistent weak layers (Problem 2) lower on slopes, causing a larger destructive avalanche.  

    (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.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    What is it?  We're faced with two distinct persistent slab scenarios:

    1. Surface hoar: The most recent human-triggered avalanche occurred Sunday on a sparsely treed, sheltered slope near Titus Ridge on Galena Summit (see photo to right/above). The 1-2 foot thick avalanche failed on a buried layer of surface hoar on a N-NE aspect near 9100'. This weak layer remains capable of producing avalanches on some slopes steeper than about 35 degrees.
    2.  Older weak layers—crusts and/or facets, and spotty surface hoar—exist deeper in the snowpack. These are buried beneath dense, 2-4 foot thick slabs, making them difficult to trigger but capable of producing very dangerous avalanches.

    Where is it? 

    1. Thesurface hoar is most widespread and problematic in protected, middle-elevation terrain that faces E-N-W. Surface hoar is a tricky weak layer. It can be "spotty" in its distribution—it may exist on some slopes, but not others. 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. The older, more deeply buried weak layers are most widespread, and suspect,  in rocky, wind-affected, upper elevation terrain where snowpack depths are less than about 4 feet.

    How can you recognize it?  Assume the persistent slab issues exist until proven otherwise. You may or may not experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability. The layer of surface hoar is subtle and may not "jump out at you" when searching for it in a snowpit (see photo here). Wind-swept, upper elevation slopes with thin, variable snowpack depths are likely to harbor the older crust and facet layers.          

    How can you manage it?  

    1. Buried surface hoar: You can reduce your risk by avoiding shady slopes (facing E-N-W) that are very steep (greater than about 35 degrees)—especially those with ugly consequences if you are caught in an avalanche. While the observed avalanche activity points to the layer being more common on sheltered slopes, don't rule out its existence in terrain exposed to the wind. These avalanches may break wider than expected or higher on the slope above you. 
    2. Older weak layers: Although not likely, you could trigger a  large slide on slopes steeper than about 35 degrees in rocky, wind-affected, alpine terrain. Slopes like these have variable snow depths, with thinner areas of the snowpack that allow us to impact deeper weak layers. You can reduce your risk by steering clear of large, recently wind-loaded avalanche paths that are peppered with rocks sticking up above the surface (photo), a great indicator of variable snowpack depths. 

    (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.

Avalanche Discussion

Over the past month, we've seen a significant divergence in the character of the snowpack within and between forecast zones. In a broad sense, you can lump them into two categories: shallow and deep. Why does depth matter? Persistent weak layers tend to survive or thrive in shallow snowpacks. Where the snowpack is deeper, buried persistent weak layers tend to strengthen over time. The Soldier and Wood River Valley Forecast Zone straddles the boundary between these categories. 

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 snowpack.

On the western side of this zone (Dollarhide and west to the Soldiers), the snowpack is thicker (4-6 feet deep), and the slabs above the weak layers remain intact. Weak layers buried in November and December lie beneath very dense, heavy slabs of snow. Impacting these weak layers is less likely. However, the prominent weak layer that was buried in January is sitting under a 1-2 foot thick slab; impacting it remains a real possibility. This layer is ugliest on wind-protected, shaded slopes (those on the northern half of the compass) where surface hoar formed. However, a pattern of unstable snowpack test scores on sunnier slopes—where facets and surface hoar lie above a crust—is worth noting. 

On top of these weak layers, a few generations of wind slabs formed in the past week. The most recently formed slabs are likely to be softer and more reactive to your weight. However, the large, recent slide in the Soldier Mtns probably involved rock-hard snow that drifted onto the slope last week; triggering beasts like that is a possibility. Triggered wind slab avalanches 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. 

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