Sawtooth & Western Smoky Mtns

Lawinenprobleme

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  2–3

  What is it?  2-4 foot thick slabs overlie persistent weak layers (sugary facets, surface hoar, and/or crusts) on most aspects and elevations. Wind-loaded slopes are most dangerous, and slopes sheltered from the wind are suspect. Recent snowfall is stressing the buried weak layers. 

  Where is it?  This problem is widespread through all elevations and most aspects. While the vast majority of December's avalanche activity occurred on W-N-E aspects (see graphic below), observers have reported snowpack collapsing and/or poor snowpack test scores on sunnier SW-S-SE slopes. Wind-loaded slopes are more dangerous than sheltered terrain. In the Sawtooth Mtns, expect "spindrift" to build slabs and stress buried weak layers in protected bowls and cirques below large cliff faces and couloirs. 

  How can you recognize it?  This persistent slab problem is widespread; assume it exists on all slopes until proven otherwise. You may experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability. Wind-loaded areas feel stiffer under your skis or sled and keep you from easily sinking into the snowpack.         

  How can you manage it?  Unfortunately, avoiding slopes steep enough to slide is the only surefire way to manage this problem.Persistent slab avalanches are tricky. If you're playing near steep slopes, you could trigger slides remotely (from gentler terrain above, below, and to the sides of steep slopes—explanatory video here). These avalanches may break wider than expected or higher on the slope above you. 

  

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1–2

  What is it?  We observed several wind slab avalanches in the Boulder and Sawtooth Mtns in recent days (see photo). Yesterday, Chris steered clear of freshly wind-loaded slopes on Copper Mountain. Last night, strong, gusty winds formed or built hard and soft wind slabs. Some slabs have been growing for a few days. The wind slabs lie above a variable surface (facets, some surface hoar, crusts, "regular" snow, wind-polished surfaces, etc); some slabs will be easy to trigger while others may be "stubborn" or hard to trigger. Smaller wind slab avalanches could "step down", triggering the large persistent slab avalanches described in Problem 1. 

  Where is it?  Strong and extreme winds can form slabs in unusual and unpredictable locations. You may find them far below ridgelines, on the sides of gullies, and near prominent terrain features in normally sheltered areas.

  How can you recognize it?  Cracks shooting out from your skis or sled are an obvious sign of instability. Watch for drifts, dunes, and ripples on the snow surface. Wind slabs can have a smooth, chalky appearance and feel and sound hollow, like a drum. Wind-deposited snow will be stiffer and keep your skis or snowmobile closer to the surface.       

  How can you manage it?  Given the increased chances of triggering a large persistent slab avalanche on wind-loaded slopes, the prudent move is to avoid obviously wind-loaded avalanche terrain. Hard slabs are notoriously unpredictable; these avalanches may break wider than expected or higher on the slope above you.