Bitterroot

Lawinenprobleme

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2

  Overnight, winds remained steady out of the northwest with speeds in the low 20s at ridgetop. These speeds are very effective at transporting snow and building slabs. Today, expect to find new slabs that formed overnight, mixed with slabs that formed yesterday.

  Wind slabs can be identified by their smooth or pillow like appearance and often form just below ridgelines, in gullies, and below convex rollovers. If you see signs of instability like recent avalanches or cracking around your skis or sled, stick to low angle slopes less than 30 degrees.

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1.5–2.5

  Larger avalanches failing 2-4 feet deep on weak snow surrounding crusts are possible. Multiple snowpits across the Rattlesnake and Bitterroot have shown poor snowpack structure with reactivity and full propagation in snowpit tests. We have not seen any avalanches reported on this layer yet, but all the ingredients for a larger avalanche are present. As more storms continue to load this layer with increasing weight, we could see conditions spike and avalanches become more widespread on this layer. 

  This layer formed during the mid December rain events that were followed by cold snow. At the boundary between warm wet snow and cold new snow, weak snow developed directly above and below a crust. This problem can be highly elevation dependent, but be suspicious of any slope above 6500’ with a buried crust in the snowpack. 

  At the highest elevation north facing slopes, above the rain line from the warm December storms, there is still some weak snow near the ground (depth hoar). This snow is showing signs of rounding or gaining strength but in specific terrain, very large avalanches failing at the ground are possible. 

  Whumfing and collapsing are red flags for persistent weak layers, but you may not see any signs of instability before triggering an avalanche on these layers.  Dig in the snow and look for poor snowpack structure with a slab above a weak, sugary layer. Manage the problem with slope angle and stick to slopes less than 30 degrees. Keep in mind that persistent slabs could also be triggered remotely, or smaller avalanches can step down and trigger a larger persistent slab avalanche.