Bulletin d’avalanche

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Your odds of triggering a large avalanche are greatest on slopes where you find wind-drifted snow. Avalanches are possible, but far less likely, in steep terrain sheltered from the wind. You may be able to trigger avalanches remotely—from gentler terrain below, above, and to the sides of steep slopes.  

Conditions are most dangerous in the Soldier Mountains due to more recent snowfall and stronger winds.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    Yesterday, a skier-triggered avalanche was reported near Galena Pass (photo). Tuesday, snowmobilers in Smiley Ck triggered a thin but wide avalanche from flat terrain near the base of the slope (photo above/right). Both of these slides released on weak snow buried about 1-1.5' deep. At this depth, touchy layers of surface hoar have been observed on shadier, sheltered slopes beneath the recent storm snow (Banner Summit, Titus Ridge, Soldiers). 

    Below the storm snow, a myriad of weak layers (sugary facets, surface hoar, and/or crusts) exist on a variety of aspects in the mid and upper snowpack. Yesterday, I observed sled-triggered cracks breaking on mid-pack weak layers buried 2.5' deep (photo). Skiers in the Pioneers felt multiple large rumbling collapses, likely involving the same, weak snow. 

    Assume that most slopes harbor one or more of these weak layers. You're most likely to trigger avalanches on slopes where the wind has formed drifts or slabs or stiffened the snow at the surface (example). Wind-exposed bowls and slopes near ridgelines, prominent gullies, and chutes are most likely to produce large avalanches.

    Persistent slab avalanches are tricky. These avalanches may break wider than expected or higher on the slope above you. You may be able to trigger avalanches remotely—from gentler terrain below, above, and to the sides of steep slopes.  You can significantly reduce your risk by steering clear of steep, wind-affected terrain. 

    ADDITIONAL DISCUSSION: While triggering slides on faceted snow near the base of the snowpack is unlikely, it can't be ruled out in steep, rocky, wind-affected alpine terrain. Slopes like these have variable snow depths, and thinner snowpack areas allow our weight to more easily impact deeply buried weak layers.

    (1/10/2023) Snowmobilers remotely triggered this thin but wide avalanche from flat terrain a ways below the slide. Smiley Ck drainage, NW aspect near 9000'. 

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Expect to find 1-3 foot thick wind slabs in exposed terrain. Yesterday, riders in the Soldier Mtns triggered a large wind slab avalanche from a flat ridgetop (photo above/right). Numerous, small wind slab avalanches occurred yesterday morning. Similar human-triggered avalanches are possible again today. 

    Wind slabs are the largest and most widespread at upper elevations. You may also encounter smaller wind slabs in obviously wind-affected terrain right down to the valley floor (Bellevue, Soldiers). Look for them near ridgelines, on the sides of gullies, and near prominent terrain features. Shifting wind directions in the past week may have formed thick or thin slabs on a variety of aspects. 

    Cracks shooting out from your skis or sled are an obvious sign of instability. Watch for drifts, dunes, and ripples on the snow surface (Sawtooths, Soldiers). 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. Avoid steep slopes with thick or hard wind slabs. Any triggered wind slab could "step-down" to buried persistent weak layers (Problem 1), causing a larger and more destructive avalanche.  

    (1/11/2023) Riders in the Soldier Mtns remotely triggered this wind slab avalanche from atop the ridge. SE aspect at 8,200'. This and many nearby slopes showed signs of heavy wind-loading from strong NW wind early in the morning on Jan. 11th.

Avalanche Discussion

Today's weather should not have a dramatic impact on avalanche conditions. The avalanche danger has decreased to MODERATE. This is a full danger step lower than yesterday, but triggering a large avalanche remains possible. Here are some points to consider:

Weak Layer Complexity: A few weeks ago, in a conversation with Ben, he said "I feel like the weather does two things here, create weak layers or bury them." That has certainly been the case this winter. Keeping track of these layers, their distribution, and their sensitivity is a full-time job. The complexity and spatial variability make slope scale stability assessment a nearly impossible task. The safest bet is to assume one or more of these layers exist and are capable of producing a large avalanche. 

Wind Slabs: At least two generations of wind slabs exist. One formed during heavy snowfall and S-SE wind earlier this week. Another formed overnight and into the morning Wednesday as wind shifted to blow from the NW. This second round of wind produced numerous small wind slab avalanches in our southern zones and was responsible for yesterday's rider-triggered avalanche in the Soldier Mtns. The 180-degree shift in wind means you could find slabs on multiple aspects and even some at lower elevations near the mouths of large drainages.

Warm Sunshine: Yesterday was warm and many mountain locations saw multiple hours of direct sunshine. The heat from the sun likely peeled off the "easy pickings" in the form of roller balls and small wet loose avalanches. However, there was some cloud cover yesterday, and a little well-timed shade may have saved some steep, sunny slopes. Today's temperatures are expected to be warmer than yesterday, and skies should clear in the afternoon. Keep the overhead hazard of a wet loose avalanche in mind today if you're traveling near or under steep, rocky, sun-drenched slopes. 

Despite the danger "drop" it's more accurate to imagine it on a "slow decline". Carefully consider the consequences of triggering a slide before committing to a steep slope. Choose simple, safer slopes that avoid terrain traps like stands of trees, cliffs or creek bottoms where debris piles deep.

Régions couvertes