Central Sierra Nevada

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

  2–3

  Intense blowing snow and wind slab avalanches were reported yesterday. Ongoing winds today combined with new snowfall will continue to blow and drift substantial amounts of snow. Wind slabs will continue to form in lee areas near ridgelines today mainly near treeline and above treeline on NW-N-NE-E-SE aspects. Wind slabs may also form to a lesser extent in below treeline areas due to the strength of the winds.  Wind slab avalanches are expected to be large to very large in size today. Natural avalanches are possible, human triggered avalanches are likely.

  Use blowing snow, wind drifted pillows of snow, cornices above a slope, and wind textured snow surfaces as clues to indicate where unstable wind slabs may exist.  Plan routes that provide a buffer and margin for error when navigating around slopes below cornices or any other wind loaded terrain.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Possible

  Dimensione

  2–3

  There are some indications of an emerging persistent slab avalanche problem with localized distribution. Faceting along the thin Jan 4 rain crust and unstable snowpit test results have been reported from NW-N-NE aspects in the 7,500' to 8,300' elevation range in the Border Ruffian and Blues Lakes areas south of Carson Pass. Observations targeting this layer at various elevations in the Independence Lake, Donner Summit, and Mount Rose zones have not revealed any faceting or weakness on this specific layer. Substantial unknowns remain in regard to the areas where this layer is weak and problematic.

  In any areas where this layer is weak and problematic, it currently is and will continue to receive stress from the load of new snow and possibly rain during the current storm cycle. An avalanche that fails on this crust/facet layer would fail at a minimum of 2 feet deep in the snowpack, likely have wide propagation, and could be triggered from low on a slope or from the side. If you trigger any snowpack collapses, whumpfing noises, or snow surface cracking, pull back into lower angle terrain and consider avoiding NW-N-NE aspect avalanche terrain in the area.