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

  Expect to trigger wind slabs up to 3 feet thick in exposed terrain, especially near ridgelines. Natural avalanches are possible. The slabs will be larger, more widespread, and probably easier to trigger both as you climb in elevation and as this afternoon's wind builds new and existing slabs. With 6-12" of recent snowfall to blow around, today's northerly winds have plenty of "ammunition" to form slabs and drifts. In the craggy Sawtooth Mtns, you may also find dense pillows of spin-drifted snow on aprons below large cliff faces, chutes, and couloirs.

  Some of the wind slabs and wind-stiffened snow overlies crusts and crust + facet combinations; in these areas, avalanches could be very easy to trigger, could release naturally, and could break wider than expected. Avalanches are possible in areas where the wind has subtly stiffened the snow near the surface. Small chunks of cornice that you break off or that fall naturally could trigger wind slabs on the slopes beneath them. 

  Fortunately, managing this problem is straightforward; avoiding wind-loaded slopes will significantly reduce the chances you find trouble. Watch for fresh cornices, dunes, rippled snow surfaces, and areas with stiffer snow surfaces. These are clues that the wind has been at work. Cracks shooting out in front of your skis or boards mean you've probably found a wind slab.

  Additional Discussion: Any periods of unobscured sunshine will raise the threat of natural or human triggered loose snow avalanches (sluffs). These are most likely on slopes shelted from the wind while they are directly facing the sun. Most of these slides will be small, but large avalanche paths facing the southern half of the compass should be treated with respect. The sluffs could run far on crusts beneath them and can be deceptively powerful. Today is not a good day to hang out in or beneath big avalanche paths. 

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  It would take some bad luck, but triggering a large, destructive avalanche isn't off the table yet. These slides would fail on persistent weak layers (crusts, crusts and facets, or facets) in the middle or bottom of the snowpack. You're most likely to trigger them on middle and upper elevation slopes with recent wind-loading.  

  Persistent Slab avalanches can release in surprising ways. You can trigger them from flat or low-angle terrain long distances away from steep slopes, and they can break far above you. They can break hundreds or thousands of feet wide. Before triggering an avalanche, you probably won't experience snowpack collapsing or other obvious signs of instability. 

  You're most likely to trigger one of these beasts in steep, rocky, wind-swept alpine terrain. Here, thin areas of the snowpack make it easier to trigger avalanches.