Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Conditions are dangerous on slopes where the wind has formed drifts or stiffened the snow surface. While the chance of triggering a large avalanche is highest in exposed, windy areas, avalanches are also possible in steep, wind-sheltered terrain. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

Conditions are most dangerous in the Soldier Mtns and near Dollarhide Summit where the most snow fell.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    Weak snow layers of surface hoar, facets, and crusts exist in the upper 1-3' of the snowpack. These layers caused cracking (observation), and collapsing (observation) near Galena Summit yesterday. They've also produced repeated unstable snowpack test scores both before (here, here), and after our recent storm (here, here). 

    We've found these layers across the forecast area, but their sensitivity varies from slope to slope. The patterns are complex. The development and preservation of these types of weak layers are highly dependent on wind and sun exposure. Expect to find them in some form or another on all aspects at middle and upper elevations. While they also exist on lower elevation slopes, recent rain and warm temperatures have helped them to heal.

    You're most likely to trigger an avalanche involving this weak snow in recently wind-loaded terrain. You may not observe hard signs of instability like snowpack cracking or collapsing. But the safe bet is to assume these layers exist. Before committing to skiing or riding a slope consider the consequences of triggering a 2' thick avalanche. Is the run-out clean, or will a slide strain you through trees or pile debris into a terrain trap below?

    ADDITIONAL DISCUSSION: A widespread weak layer of snow exists near the base of the snowpack. This layer is ugliest on W-N-E aspects. This layer is deeply buried and harder to trigger. While triggering an avalanche on this layer is increasingly unlikely, the image above/right illustrates the very large and deadly slide this layer will produce. 

    (12/26/2022) Motorized users remotely triggered this large avalanche north of this zone in the White Cloud Mtns while riding in flatter terrain an estimated 1/4 mile away. Above Washington Lake, 10,500', E-NE aspect.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Strong wind Tuesday formed soft and hard wind slabs in exposed terrain. You're most likely to encounter a sensitive wind slab at upper elevations, but some may exist on exposed middle elevation slopes. Look for them near ridgelines or along the sides of cross-loaded gullies. 

    Low density snow near the surface may make fresh wind deposits difficult to identify. Your best bet is to look for larger drifts, or dunes at the snow surface. Stomping on small wind lips or cornices can give you information on the sensitivity and depth of the drifts. 

    Cracks shooting out from your skis or sled are an obvious sign of instability. This problem could be dangerous alone, but any triggered wind slab has the distinct possibility of "stepping down" to break on weak layers deeper in the snowpack.

    (12/28/2022) Small avalanche on NE facing slope of Griffin Butte @ 7,400'.

Avalanche Discussion

Avoiding recently wind-loaded terrain will greatly reduce your odds of triggering a large and dangerous avalanche. Low density snowfall masked many of these wind-drifts and it will take a little more sleuthing to uncover where slabs are hiding. Without a doubt, my avalanche antenna will perk up as I climb out of sheltered low elevations and into any exposed terrain. I'll be looking for larger clues, like recent avalanches, dunes, or recent cornice growth to help identify wind-loaded terrain.

The avalanche problems listed above (although separate) should be considered together. It's where they overlap that conditions will be the most dangerous. True wind slab avalanches are likely in upper elevations, but my concern is that a large one will provide a trigger as it reaches a slope with a well-connected weak layer buried deeper in the snowpack. As I pointed out in the problem text above, the exact pattern of weak snow layers in the upper 1-3' of the snowpack is impossible to know and will vary from slope to slope. The safe bet is to assume one or more of these layers exist. 

At elevations below about 7,000' heavy rain saturated the snowpack on many slopes, and the odds you find a combination of a slab and a well-preserved weak layer are low. Above that, I'll assume I could encounter a slope capable of a large avalanche and I'll use safer terrain to help reduce my risk. Lower-angled slopes are always an option. Short slopes with clean runouts are safer than those that end in terrain traps—amplifying our mistakes. There's some great riding to be had today, but don't let soft snow at the surface cloud your good judgment. 

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