Sawtooth & Western Smoky Mtns

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2

  Today's 1-3 inches of fresh snow will add to the 15-20 inches that fell in the past week You can expect to find a wide range of problems involving this recent snow. These broadly fall into two categories:

  SLABS: Periods of shifting winds have built several generations of wind slabs at the surface. Look for drifts, dunes, and rippled snow surfaces as an indication that the wind has been at work, but expect much of this evidence to be masked by today's snowfall. In the steep, rocky terrain of the Sawtooths, sensitive slabs commonly form below couloirs and large cliffs. Cracks shooting out from your skis or machine are a clear sign that you've found an unstable slab that could be triggered on steeper slopes. Even in terrain that is apparently sheltered from the wind, you can trigger slabs that fail at the base of the February snow (see photo at right/above). The variable layers of weak snow that are generating this problem appear to be at their worst where either sun crusts or rain crusts exist at this interface. Read more about the budding persistent slab problem in the Forecast Discussion below. 

  LOOSE SNOW: In terrain sheltered from the wind, expect small loose snow avalanches to be easy to trigger. If you're seeking out cold, crust-free snow on northerly aspects these sluffs will have a dry character. On slopes where the sun is warming up and melting the snow surface this afternoon, these loose snow slides will have a wet character. If you're finding moist/wet snow at the surface or if you are seeing wet balls of snow rolling down the slope this type of slide is coming onto the menu. Loose snow slides will start out small, but can pick up steam and run quickly thanks to the stiff and crusty surfaces underneath the recent snow. The steep terrain in the Sawtooths is great at producing both dry and wet loose avalanches that grow in size quickly. 

  Avalanches involving the new snow will range from small to large enough to bury you. Avalanches failing near the surface can be effective triggers for avalanches that fail on the deeper weak layer described below. 

  ADDITIONAL DISCUSSION - WET SNOW ISSUES: On slopes where the sun is warming up and melting the snow surface this afternoon, loose snow slides are possible and will have a wet character. If you're finding moist/wet snow at the surface or if you are seeing wet balls of snow rolling down the slope this type of slide is coming onto the menu. Loose snow slides will start out small, but can pick up steam and run quickly thanks to the stiff and crusty surfaces underneath the recent snow. 

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  Under the recent storm snow, you will find thick, very dense slabs resting on layers of weak snow. This combo has produced dozens of recent avalanches in the neighboring Galena Summit and Eastern Mtns zone. Many of these slides have been large enough to snap mature trees and destroy large vehicles. Our limited observations indicate that recent activity has been less widespread in this zone. The photo at right/above shows a large avalanche that appears to have failed on one of these deeper weak layers during the recent storm.

  If you dig down, you'll find thick piles of facets with or without surface hoar on shaded aspects, and crust+facet combinations on slopes that get more sun. Recent avalanche activity has been much more widespread on shady slopes, but a few large avalanches failing on slopes that face the sun indicate that this problem exists in those areas as well. 

  Because the slabs on top of this weak layer are so dense, and the new snow is so soft and fluffy, you aren't likely to encounter many or any signs of instability before triggering a large, potentially unsurvivable avalanche. Keep this weak snow close to mind when you are moving through the mountains. The only guaranteed way to avoid this problem is to steer clear of avalanche terrain and slopes threatened by overhead hazard. Any avalanche that fails on this weak layer will be large and destructive, and slides can be triggered from long distances away (remote triggering).