Sawtooth & Western Smoky Mtns

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  On Tuesday, a skier triggered a wind slab avalanche in the southern Sawtooths while entering steep, exposed terrain. Today, triggering similar avalanches remains possible.

  Recent wind and snowfall formed slabs and drifts up to 3 feet thick in upper and some middle elevation locations. Some slabs overlie crusts and/or thin layers of weak, faceted snow; the wind slabs could be easy to trigger and break wider than expected on some slopes. 

  • Look for shooting cracks, smooth dunes, textured snow surfaces, or cornices. 
  • Feel for changing surface conditions while entering more exposed terrain. Wind slabs will feel firmer than snow in sheltered locations. 

  If you encounter these signs, reduce your odds of triggering a wind slab by moving to lower-angle terrain sheltered from the wind.

  Additional discussion: It is possible trigger 1.5-2’ thick avalanches in terrain sheltered from the wind. These avalanches could fail on a variety of old snow surfaces, such as crust, facets, or a combination of both. Additionally, loose snow avalanches (sluffs) are possible in steep terrain. Sluffs could trigger larger slab avalanches lower on aprons and in alpine bowls.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  1.5–2.5

  While unlikely, we can't write off triggering large avalanches in middle and upper elevation terrain while the snow keeps piling up. Unfortunately, you probably won't receive any obvious signs of instability before triggering one of these lingering monsters. We are most concerned with a layer of weak facets found near the ground on middle and upper elevation slopes, especially those facing away from the sun.

  Triggering a slide on this layer is most likely in rocky, heavily wind-affected areas where the snowpack depth is variable, and in more sheltered terrain where the snowpack is around 3 feet deep (read the Forecast Discussion for details). Smaller wind slab avalanches or sluffs (Problem 1 above) could "step-down" as they travel down slope, triggering much larger Persistent Slab avalanches.