Sawtooth & Western Smoky Mtns

Problèmes avalancheux

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Likely

  Taille

  1.5–2

  Expect to find sensitive slabs in wind-loaded terrain. Tuesday, Ben observed a large avalanche on the north side of Copper Mtn near Banner Summit (report). The slide was triggered remotely from low-angle terrain and released on a wind-loaded slope just below the ridge. You could trigger similar avalanches today as an uptick in wind forms a fresh batch of wind slabs this afternoon.

  Slabs will be thicker, wider, and more dangerous at windier, upper elevations. Look for them near ridgelines and along mid-slope terrain features like ribs and gullies. Stiff slabs may extend into wind-exposed middle elevation terrain. Some wind slabs sit atop weak snow (facets, surface hoar, crusts), which may make them more sensitive to triggering and could cause them to break wider than expected.

  Snowpack collapsing or cracks shooting from your skis or sled are obvious signs of instability. Low density snowfall and shifting, intermittent wind may mask the usual clues that the wind has been at work. This may make it difficult to identify a recently wind loaded slope from a distance. Even subtle wind affect over the past ten days may be enough to stiffen the snow and increase your odds of triggering a slide.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  1.5–2.5

  You could trigger 1-3' thick avalanches on buried weak layers. The weight of recent storm snow is overloading these layers, which include: sugary facets, crusts, or crust + facet combinations. These slides are possible in both obviously wind-loaded and sheltered terrain (photo above/right). Today's storm may release wind slab avalanches, cornices, or sluffs that can act as triggers stepping down to these weak layers to produce a large, dangerous slide. 

  Middle and upper elevation slopes are the most dangerous because more snow fell there in the past few days. Weak layers of snow exist below the recent storm snow and deeper in the snowpack (photo). The distribution, character, and sensitivity of these layers vary from slope to slope, and stability tests are of limited use. Your best bet is to assume this problem exists until proven otherwise. 

  Persistent slab avalanches behave in unpredictable ways. You can trigger them from a distance, from gentle terrain above, below, or to the sides of steep slopes. These slides may break wider than expected or higher on the slope above you. The first skier or rider may not trigger an avalanche on an unstable slope. Do not assume tracks mean a slope is safe. You can reduce your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if you are caught in a slide.