Sawtooth & Western Smoky Mtns

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  2–3

  Accumulated snowfall during the day is expected to tip the balance on a pair of buried weak layers, making triggering 2-5' slabs of snow very likely and very large natural avalanches likely. Triggering these avalanches is most likely in wind-loaded terrain, but will also be quite possible in sheltered terrain. Persistent Slabs can release in surprising ways. They can be much wider than expected and be triggered remotely—from flat terrain below, above, and to the sides of steep slopes.

  Two known buried persistent weak layers will be tested throughout this storm. Last week's storm snow buried weak facets, surface hoar, and crust-facet combinations on many middle and upper-elevation slopes. More deeply buried weak layers that formed during the extended Jan-Feb drought (facets, crust + facets, surface hoar) have not healed and remain suspect, primarily on NW-N-NE-E aspects above and below the middle-to-upper elevation transition.

  Snowpack cracking and collapsing are clear signs of unstable conditions. Avoiding being on or connected to steep slopes today is the best way to keep out of trouble.

  Additional Discussion: The chance of triggering slabs of new snow in sheltered terrain will increase throughout the day and overnight. Rising snow lines throughout the storm indicate that heavier snow will fall atop fluffier snow, quickly building unstable, dense storm slabs. Given the variety of snow surfaces the snow is falling on, they may break wider than expected and act like or trigger larger persistent slab avalanches (described above).

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1.5–2.5

  Triggering large wind slab avalanches is very likely today. Consistent W and SW winds are transporting snow and actively building fresh slabs in exposed terrain. These are most commonly found near or below ridgelines, along mid-slope ribs, and on aprons beneath chutes. Cracks shooting out in front of your sled or boards mean you've found a sensitive slab. Look for wind-affected surfaces, dunes, or drifts.  Feel for stiff slabs overlying weaker or softer snow.

  You can manage your exposure to this problem by identifying and avoiding wind-loaded slopes. Smaller wind slabs can also act as effective triggers for larger persistent slab avalanches described above.