Galena Summit & Eastern Mtns

Problemi valanghivi

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  1–2

  Expect to find sensitive slabs in both obviously wind-loaded and more sheltered terrain. Yesterday, Ben observed a large avalanche on the north side of Copper Mtn near Banner Summit (photo). Monday in Frenchman Ck, a snowmobiler remotely triggered a slab avalanche that released in wind-loaded terrain below a cliff. You could trigger similar avalanches today.

  Yesterday's blowing and drifting snow continued to build sensitive slabs. Triggered slides 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 (photo, photo). Some wind slabs formed over 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. Ample low density snowfall and shifting 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.

  ADDITIONAL DISCUSSION: Multiple layers of weak snow exist in the upper 1.5-2.5 feet of the snowpack. Continued snowfall is building a thicker, stiffer slab above these layers, pushing some of them to their breaking point. While most dangerous in wind-loaded terrain, you could also trigger a large slab avalanche involving this weak snow in areas that are protected from the wind. This scenario is most likely in the White Clouds, Smokys, and in the mountains surrounding Galena Summit. See the forecast discussion for details. Wind slab avalanches, cornice breaks, or sluffs can act as triggers stepping down to these weak layers to produce a very dangerous slide. 

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Unlikely

  Dimensione

  1.5–2.5

  Triggering a large persistent slab avalanche on weak, sugary facets buried deeper in the snowpack would take some bad luck. The video to the right/above describes this problem. Where are you most likely to find this scenario? On slopes with all or most of the following characteristics:

  • Wind-swept alpine terrain, especially in the Pioneer, Boulder, and White Cloud Mountains.
  • Steeper than about 35 degrees.
  • Variable snowpack depths with areas less than 2 feet deep and/or rocks poking through the snow surface.
  • Large, hard wind features somewhere on the slope.

  Don't expect to see or hear obvious signs of instability (snowpack collapsing or cracking) before a large avalanche releases. Snowpack stability tests are of little use in situations like this. The best way to manage this problem is to avoid terrain that checks all or most of the "boxes" above.