Sawtooth & Western Smoky Mtns

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1–2

  Above the rain line, different types of natural and human-triggered avalanches will become likely. Slab avalanches are most likely to release where it's "steepest and deepest": on slopes steeper than about 35 degrees, where at least 6" of snow has accumulated. The slabs will grow steadily through Monday morning. On some slopes, crusts and / or weak snow exist beneath the new snow; avalanches could be easy to trigger and may break wider than you expect. A couple types of slab avalanches to watch for: 

  • Storm Slabs: The dense, damp storm snow will forms slabs on most slopes, including slopes that are completely sheltered from the wind. These avalanches could be big enough to catch, carry, and injure people. 
  • Wind Slabs: At upper elevations, the new snow will be less dense, perfect for expected moderate to strong winds to form wind slabs up to 2 feet thick. You may find some wind slabs at middle elevations. Watch for fresh drifts and slabs below ridgelines, on the sides of cross-loaded gullies, and on aprons at the bottom of steep alpine cirques and large cliff faces.

  Cracks shooting out from your sled or boards are a clear sign you've found a slab and should stick to gentle terrain to avoid trouble. Natural loose snow sluffs or cornice fall could also trigger slab avalanches; minimize the time you spend in the runouts of large avalanche paths. 

  Avalanche conditions and stability will deteriorate this afternoon and tonight. Don't assume the avalanche path you played in this morning is still safe near dark. 

  Additional Discussion - Persistent Slabs:  It would take some bad luck to trigger a huge, 2-6 foot thick avalanche on weak layers that formed in January. But, the consequences would be devastating. You're most likely to trigger one of these beasts on very steep, NW-E facing, middle and upper elevation slopes. Slopes where the wind frequently blows have variable snowpack depths (deep and shallow) and a better chance of triggering these large avalanches. Triggering a large, Persistent Slab is most likely in the southern reaches of this zone. 

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1–2

  Natural wet avalanches are very likely to release where significant rain falls. The rain line line is expected to rise to near or above 7500' this afternoon. The wet slides are most likely on slopes steeper than about 35 degrees. Most of these avalanches will be relatively small, but some could gouge down into a damp snowpack, flank out as slabs, and become large enough to break trees. 

  During rain-on-dry-snow events, snow stability is unpredictable and can change rapidly. After hours of steady rainfall and no avalanches, a widespread avalanche cycle can occur as if a switch has been flipped. The safe move is to avoid playing on or under large or consequential avalanche paths where steady rain falls. 

  Roof avalanches: The warm temperatures and rain will make large roof avalanches likely this afternoon through Monday. Roof avalanches have killed people in Idaho and neighboring states, and several close calls have occurred locally in recent years. Click here for information and photos.