Sawtooth & Western Smoky Mtns

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1.5–2

  8-14" of snow (0.6-0.9" 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 SW-S-SE. As I write this, 1-2 foot thick wind slabs are building (and potentially failing naturally) in terrain exposed to the wind. These slabs will be largest, thickest, and most common in upper elevation terrain, but will extend down into middle elevation terrain as well, thanks to the strength of the wind. Expect them to be easy to trigger where you find them.

  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.

  Wind slabs commonly form 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. Evidence of wind-loading may be subtle or may be masked by additional snow that fell after slabs formed. 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

  Likely

  Size

  1.5–2.5

  Layers of weak snow in the upper snowpack can produce wide, destructive 2-3+' 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.