Sawtooth & Western Smoky Mtns

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  What and where is it? Several large avalanches released naturally near the end of the recent storm. In recent days, snowfall and strong, gusty wind formed 1-2 foot thick wind slabs below corniced and exposed ridgelines, on the sides of cross-loaded gullies, and in cirques below steep faces and large cliff bands. The slabs are largest and most widespread at upper elevations but also exist in some exposed middle elevation terrain. You could find wind slabs at ridgelines and lower on slopes than you'd expect.

  How do we recognize and manage it? 

  • Look for dunes, textured snow surfaces, and cornices. 
  • Feel for changing surface conditions. Wind slabs are stiffer than the powder found in sheltered locations. They may feel or sound hollow or "drummy."

  Fortunately, the wind slabs are fairly easy to identify and avoid. Give cornices a wide berth; they can break on their own or with the weight of you or your sled. Falling cornices are great triggers for wind slab avalanches. Snowpack cracking and collapsing are clear signs of unstable conditions.  

  Additional Discussion - Persistent Slabs:  Although it would take some bad luck, you could trigger a much larger, 2-4 ft thick persistent slab avalanche on buried weak layers (sugary facets, surface hoar, and crust + facet combinations). This problem is worst on recently wind-loaded, middle and upper elevation slopes facing NW-N-NE-E. Don't expect to experience obvious signs of instability; the first sign of instability you see could be the avalanche you trigger. 

   

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  What and where is it?  Steamy, sauna-like conditions and periods of sunshine could produce natural wet loose avalanches. The majority of these slides should be relatively small, involving the recent snowfall. You're most likely to trigger or see wet loose avalanches on very steep, wind-protected slopes where more than about 6" of snow fell during the last storm. 

  How do we recognize and manage it? Sun and heat can rapidly produce loose snow avalanche instabilities. Watch for rollerballs or pinwheels moving downslope, signs the surface snow is moist. Move to cooler slopes or gentler terrain if the surface snow gets wet and mushy. Loose snow avalanches begin as a point, entrain snow as they move downhill, and are surprisingly difficult to escape. Cornices could break on their own, producing loose snow avalanches on steep slopes under them.  Don't linger on or below large avalanche paths with damp or moist surface conditions, especially slopes guarded by large cornices.