Boletín de aludes

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Fri
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

To reduce the chance of triggering avalanches, avoid slopes where the wind recently formed drifts or slabs. In areas more protected from the wind, triggering avalanches is far less likely. Pay attention to the consequences of being caught in even small slides in terrain with rocks, cliffs, trees, and terrain traps.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    What is it? Yesterday natural avalanches could be seen in the mountains surrounding Hailey (picture to right/above). The winds in the Soldier Mtns were even more robust than in the Wood River Valley. Expect to find isolated, hard wind slabs in exposed terrain. Though not huge, these wind slabs could be sensitive to your weight and have added weight to the buried weak layers described in Avalanche Problem 2. 

    Where is it?  You may find wind slabs near ridgelines, on the sides of gullies and chutes, and near prominent mid-slope 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 on or closer to the surface.       

    How can you manage it?  The easy move is to avoid obviously wind-loaded slopes steeper than about 35 degrees. Hard slab avalanches can behave unpredictably, breaking above skiers and riders. Small triggered wind slabs can potentially entrain snow or "step-down" to buried persistent weak layers (Problem 2) lower on slopes, causing a larger destructive avalanche.  

    (2/8/23) This wind slab released on an east-facing slope near 6200' above the Big Wood River in Hailey. This avalanche likely occurred in the early morning of Feb. 8 with increased NW winds.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1.5–2

    What is it?  This zone has widely varying conditions as you travel from E to W. In the mountains above the Wood River Valley, recent dry weather has produced a snowpack that is weak and faceted but generally lacks a slab above the weaker snow.  The important exception is wind-affected slopes where you find recent or past wind-loading. Yesterday both natural and skier-triggered avalanches involved weak surface snow creating small loose avalanches (see Forecast Discussion below for more information). 

    In the western portion of this zone, including Dollarhide Summit and the Soldier Mtns, conditions are more complex. Multiple weak layers exist in the snowpack. Some are just being buried by recent storms in the last couple of weeks. The most prominent of these is buried surface hoar down 1-1.5 feet on many sheltered, shady (W-N-E) slopes. This layer produced a number of triggered slides during the second half of January. Older weak layers (crusts and/or facets, occasionally surface hoar) exist deeper in the snowpack. 

    Where is it?  You're most likely to find trouble where the wind has loaded slopes or stiffened the snow surface. The buried surface hoar is most widespread in the western half of this zone in somewhat protected, middle-elevation terrain that faces W-N-E. Surface hoar is a tricky weak layer. It can be "spotty" in its distribution—it exists on some slopes, but not others.  

    How can you recognize it?   Wind-loaded slopes have harder surfaces and a distinct appearance (video to right/above). 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).          

    How can you manage it?  You can reduce your risk by avoiding very steep (greater than about 35 degrees), shady slopes (facing W-N-E) with hard or stiff wind-blown snow at the surface—especially those with ugly consequences if you are caught in an avalanche. Persistent slab avalanches may break wider than expected or higher on the slope above you. 

Avalanche Discussion

Wind-affected snow remains the most dangerous piece of the puzzle to triggering an avalanche. Slopes that house several weak layers can be stressed by this added weight on top of the existing slab. Recent storms are slowly building a slab over weak layers in the upper snowpack. We have yet to see a lot of avalanche activity on this layer, but snowpit test results continue to indicate poor results. The most recent avalanche occurred on buried surface hoar released near Titus Ridge on January 29th (report). This layer is showing signs of improvement. However, surface hoar is an unpredictable weak layer; most of us aren't ready to write it off just yet. In the Galena Summit & Eastern Mtns, and Soldiers Mtns, older weak snow exists where the snowpack is less than 3 feet thick. You are more likely to find this issue in the alpine, where slopes steeper than about 35 degrees have rocky, wind-affected thin trigger spots can be found. 

Moderate to strong northerly winds have transported new snow creating hard and soft slabs of the Forecast area. Most avalanches have been small, but where they overlay persistent slabs is the most concerning.  In the mountains surrounding the Wood River Valley, wind slabs are more dangerous than persistent slabs. 

A stockpile of cold days created an upper snowpack mainly composed of faceted snow (most prominent in the Wood River Valley). This weak snow doesn't like to bond well with other snow. Playing in terrain steeper than about 35 degrees can produce "facet-lanches" in this type of snowpack. These avalanches start at a point and entrain more weak snow as they descend the slope (see field report). They aren't usually big enough to bury you. However, they become dangerous when riders get knocked over and carried through trees, cliffs, gulleys, or other terrain traps. This loose snow problem can also occur when the intense, strong sun comes out today. Sunny, rocky slopes steeper than about 35 degrees can produce wet loose slides as the sun rotates around the compass and melts the snow. 

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