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Lawinenprobleme

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2

  Today's 3-6 inches of fresh snow will add to the 15-20 inches that fell at the end of the 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.  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. 

  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 failing on the deeper weak layer described below. 

  

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  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  2–3

  A widespread layer of weak snow rests underneath very dense, 3-4 foot thick slabs of snow here. In general, triggering these slides is not very likely because the weak layer is well-armored by the dense slab in many locations. However, if you find the trigger point for one of these monsters, the resulting slide will break wide and deep, producing a very destructive avalanche. You're most likely to trigger this type of slide in steep, rocky, wind-swept alpine terrain, where thinner areas of the snowpack give you better access to the weak layer beneath. 

  You won't see obvious signs of instability before triggering this type of slide. Assessing slope-scale stability with deeply buried weak layers is next to impossible. If you're entering avalanche terrain, this layer is likely underneath your feet. If you head into areas with thin, variable snowpacks in alpine terrain, you are playing where triggering one of these slides is most likely. Spend a little time thinking about what the terrain and snowpack look like where you are riding, and the consequences of triggering and being caught in a very large avalanche there.