Sawtooth & Western Smoky Mtns

Problemas de aludes

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Likely

  Tamaño

  2–3

  The snowpack provided some obvious clues yesterday:

  • SAC staff and public observers saw several large, powerful persistent slab avalanches (photo) that released naturally Monday night or early Tuesday.
  • While evaluating conditions on a reconnaissance mission, Sun Valley Heli Ski staff remotely triggered a persistent slab slide when the helicopter landed on a flatter slope about 1/4 mile away (photo to right/below).

  These avalanches ranged in size from "large enough to bury you" to "large enough to destroy your truck—and the garage it's parked inside." They occurred on shady, middle and upper elevation terrain where old, weak snow from October existed (see Aspect/Elevation diagram above, videos below). 

  We are not experiencing as much snowpack collapsing—an obvious sign of snowpack instability—as we were immediately after the big mid-December storm. Unfortunately, the decrease in observed snowpack collapsingdoes not mean slopes are safe. Today's snow and wind will not add a big load to the snowpack, but many slopes are still teetering on the edge of failure. You or your sled could be the proverbial straw that breaks the camel's back. 

  Do not trust any slope harboring old October snow. The old snow consists of sugary facets and crusts, and it appears as darker, crumbly layers near the ground in snowpits. Folks are finding safer conditions, and good riding and skiing, on low and middle elevation slopes that are more southerly-facing and hence lack the old October snow.   

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Possible

  Tamaño

  1–2

  Recent winds formed stiff and soft slabs near ridgelines and in exposed upper elevation terrain. Yesterday, I observed several small, natural wind slab avalanches on upper elevation slopes. Today's snowfall and wind will build existing and/or form a new generation of wind slabs. You're most likely to find windblown snow immediately below corniced ridgelines at upper elevations, but some slabs exist near prominent terrain features and in middle elevation terrain too.

  Some wind slabs may be large enough on their own to injure or bury you, but a bigger concern is the potential for weak faceted snow buried beneath (see Problem 1). Any wind slab avalanches you trigger could "step down", triggering a much thicker, wider persistent slab avalanche. 

  Look for drifts, dunes, or surface ripples and waves to help you identify wind-affected terrain. If you feel the snow stiffen under your skis or boards or see cracks shooting out in front of you, you've found a wind slab and it's time to move to gentle or more protected terrain.