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

  What and where is it?  Recent wind and snowfall may have formed slabs and drifts up to 3 feet thick in upper and some middle elevation locations. Slabs are most widespread in alpine terrain. Some slabs could 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. 

  How can we recognize and manage this problem? Fortunately, the fresh wind slabs are easy to spot and avoid. Watch for smooth pillows, dunes, and large wind features below ridgelines and cornices as well as on the sides of cross-loaded gullies and couloirs. In the craggy Sawtooth Mtns, you may find slabs where snow has "spindrifted" below large cliff faces and couloirs. If you feel the surface snow getting stiffer, it's time to pay attention. Cracks shooting out from your skis or sled are an obvious sign that you've found a wind slab. Hard wind slabs sound hollow, like a drum, and behave unpredictably; they can break above you and wider than expected. 

  Additional Discussion - Loose Snow "sluffs": Over a foot of snow has fallen recently in parts of this zone, and more is on the way. Natural and human-triggered "sluffs" will become more likely as the fresh snow piles up. Most of these slides will not be big enough to bury people, but they could knock you over and carry you where you don't want to go. Additionally, they could trigger larger slab avalanches lower on aprons and in cirques.

  

• 

  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 (see Forecast Discussion for details). Smaller wind slab avalanches or sluffs (see Problem 1 above) could "step-down" as they travel down slope, triggering much larger Persistent Slab avalanches.