Soldier & Wood River Valley Mtns

Lawinenprobleme

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  2–3

  Several weak layers exist in the upper few feet of the snowpack. Yesterday's remotely triggered slide  (pictured at right/above, details here) likely failed on one of these weak layers. Triggering an avalanche involving these layers remains a real possibility today. You're most likely to do this in steep terrain that has been recently wind-loaded, but this problem exists in sheltered terrain as well. These weak layers involve either a crust+facet combination, small facets without a crust, or surface hoar. You'll need a slope that faces the sun in order to have the crust, but the facets and surface hoar can be found around the compass. 

  We've looked for and found these layers across our forecast area, but they don't exist on all slopes. In places, the sun and the wind helped to mute the effects of some of these layers, but in others they are well preserved and quite concerning. Avalanches on persistent weak layers can be triggered from long distances away from steeper slopes ("remote triggering"). They can break wider than you might expect and pull back into gentler terrain above steeper slopes. 

  Want to significantly decrease your risk of triggering a large avalanche today? You can do so by sticking to gentler terrain, free of overhead hazards, that is sheltered from the effects of the wind. As a bonus, you'll also find the best skiing and riding here.

  ADDITIONAL DISCUSSION - WEAK SNOW NEAR THE GROUND: A layer of weak, faceted snow exists near the base of the snowpack. This layer has produced hundreds of avalanches this season. The most recent triggered avalanche involving this weak snow happened Friday in the Baker Creek drainage (photo at right/above, details here). An even larger slide was remotely triggered 6 days ago (before the recent storms) by riders in the White Clouds (photos and details here). In this zone, this weak snow is now buried 2-4 feet down, beneath a dense slab of snow. Impacting deeply buried weak layers with your weight isn't easy, but the consequences are grave. You're most likely to trigger this layer in steep, wind-affected alpine terrain where snowpack depths are variable. Here, you'll have better access to this weak snow. This is exactly the type of terrain where I triggered the avalanche in Baker Creek on Friday. Digging down to this weak snow with the track of your sled is another "great" way to impact this deep weak layer.

  

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2

  Two human-triggered avalanches occurred near Galena Summit yesterday (view details and photos in our avalanche database). They both failed near the boundary between middle and upper elevations, in terrain that is exposed to the effects of the wind. Soldier Mountain Cat Ski reported triggering sensitive wind slabs during routine control work the past two days. In the past week, 16-36" of snow (1.5-3+" snow-water equivalent) fell in this zone. Snowfall was accompanied by winds blowing from varying directions and at varying speeds. This combination built both hard and soft slabs in many different locations. Some of these have had time to bond to the surfaces they sit on, while others remain unstable, as yesterday's triggered avalanches prove. More snow fell on the western side of this zone (Baldy to Dollarhide to the Soldiers) and these drifts will be larger and more sensitive there. 

  Look and feel for evidence that the wind has been at work as you travel. Are you seeing textures on the surface, like drifts and dunes and ripples? Is the snow you are traveling through becoming denser or deeper? These are all signs the wind has been transporting snow. Remember that these indicators of wind transport may be masked by new snow on top of older slabs. Expect to find wind-affected snow in upper elevation terrain and in exposed middle elevations. Cracking and collapsing in fresh drifts are sure signs you're traveling on a sensitive slab. Slabs are most likely near and along ridgelines, and near terrain features like gullies that get cross-loaded by the wind.

  Triggered slabs have the possibility to step-down to the deeper weak layers described above. The result would be a much larger and more destructive avalanche.