Soldier & Wood River Valley Mtns

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Triggering a large wind slab avalanche is likely. Most wind slabs are building on top of persistent weak layers in the snowpack (read Problem #2 below). Because of this, the wind slabs you encounter today may behave more like persistent slabs than "simple" wind slabs. Fresh slabs will be reactive to your weight and may produce avalanches that break wider and deeper than you might expect. Triggering these avalanches remotely (from a distance above, below, or to the sides of steeper slopes) is a real possibility. Today's storm will supply some ammunition for the wind to build fresh slabs from and your likelihood of triggering slides will increase as the storm progresses. 

  Yesterday, professionals reported triggering large avalanches and seeing large natural avalanches in the Soldier Mountains (photo at right/above). These slides failed in wind-loaded terrain and very likely involved one of the layers of weak snow described below. On Friday, skiers in Indian Creek remotely triggered a large avalanche from 100' away (report, photo above/right). On Wednesday, several natural and triggered avalanches occurred on  Della Mtn near Hailey (report). Multiple large avalanches buried Warm Springs Rd with large amounts of debris (photo). All of these avalanches occurred on wind-loaded slopes.

  The wind slabs you encounter today will be largest and thickest at upper elevations, but you'll also find wind-affected snow in exposed lower and middle elevation terrain. The foothills around Fairfield and the steep slopes at the mouths of drainages that feed the Big Wood River are common locations to find these lower elevation slides. Evidence of wind-loading may be subtle, or may have been masked by additional snow that fell after slabs formed. Be on the lookout for wind slabs near ridgelines and on the sides of mid-slope features like gullies and ribs. If the snow you are moving through becomes deeper or denser you are likely traveling on a wind slab. Cracks shooting out from your skis or sled and collapsing of the snowpack are both clear indications you've found an unstable slab. Wind slabs that fail can be effective triggers for the deeper weak layers described below.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–2

  Layers of weak snow in the upper snowpack can produce 1-3' thick slab avalanches. Expect to find weak, sugary facets on shaded slopes and crust+facet sandwiches on slopes that face the sun. You're most likely to trigger a slide involving these layers in areas where the wind has built a slab on top. However, enough snow has fallen here that avalanches failing in terrain sheltered from the wind are a very real possibility.

  Variable weather in early February produced a set of variable weak layers. The nature of these layers changes from slope to slope, it's safe to assume that they exist on most all slopes. Persistent weak layers produce avalanches that fail in unpredictable ways. They can break significantly wider and deeper than you might expect, producing much larger avalanches. Avalanches failing on persistent weak layers can be triggered from gentle terrain above, below, or to the sides of steep slopes, a process known as remote triggering.

  You can reduce your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if you are caught in a slide.