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

  8-12" of snow (0.5-0.8" of SWE) fell in this zone in the last 24 hours. Wind speeds increased significantly overnight, blowing at moderate to strong speeds out of the S-SW. As I write this, large wind slabs are building (and potentially failing naturally) in terrain exposed to the wind. These slabs will be largest and thickest at upper elevations, but you'll also find wind slabs 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. Be on the lookout for wind slabs from the valley bottom to the mountain tops and expect them to be easy to trigger. 

  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.

  Friday, 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. The same day, skiers in the out-of-bounds terrain adjacent to Bald Mountain triggered a 40-foot wide avalanche that put debris on the bike path. Also Friday, skiers in Indian Creek remotely triggered a large avalanche from 100 feet away (report). 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) the same day. All of these avalanches occurred on wind-loaded slopes.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  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.

  The nature of these layers changes from slope to slope, it's safe to assume that they exist on most 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.

  The best management strategy for this persistent slab problem is terrain management. Today I recommend you choose simple, conservative terrain to play in. Pay close attention to the terrain around you and above you, and spend some time contemplating the potential outcomes of being caught in an avalanche in the terrain you are in. Cliffs, trees, and terrain traps magnify the consequence of even small slides.