Central Sierra Nevada

Problemas de aludes

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Likely

  Tamaño

  2

  Persistent slab avalanches have occurred during the past two days. This avalanche problem is clearly here as an avalanche that occurred yesterday was remote triggered from 150 yards away. The problematic weak layer of old faceted (sugary) snow, the Dec 11 PWL is buried deep in the snowpack. This weak layer has reactivated under the recent new snow load. This avalanche problem exists on W-NW-N-NE-E aspects, has a widespread distribution in below treeline and near treeline terrain, and isolated distribution above treeline.

  Whumpfing, shooting cracks, recent avalanches, and unstable snowpit test results are all indications of unstable snow in the area. Do not write off the significance of any of these clues when dealing with a persistent slab avalanche problem, even if they seem isolated. Some people saw no signs of instability yesterday while others were triggering avalanches. Don't be fooled. "Despite our best efforts to be objective, you will always be influenced by the snow that was under your feet yesterday" - Janet Kellam. Don't let post storm travel without incident cloud current decision making.

  If you choose not to scale back route choices to less than 30 degree angle slopes only, this is a difficult avalanche problem to manage. Signs of instability may or may not readily present themselves prior to triggering an avalanche. Do not underestimate potential avalanche size, potential runout distance, or the hazard from connected terrain above or to the side. Think bigger avalanche than expected. Ski, snowboard, or snowmobile slope cuts are not the right tool for this avalanche problem and are likely to lead to an accident. This is not a surface instability, this weak layer is too deep for slope cuts.

     Remote triggered persistent slab avalanche on Dec 27 on Carpenter Ridge.

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Possible

  Tamaño

  1

  Ski and snowmobile triggered wind slab avalanches occurred each of the last two days. Avalanche size has ranged from small to large depending on if the wind slab failed at the old/new snow interface up to 6 feet deep or in the upper portion of the snowpack. The old/new snow interface has been noted to contain some graupel which has the potential for slower than typical stabilization. Moderate speed E winds over the last 24 hours may have redistributed snow on the ground making wind slabs possible on all aspects above treeline and remaining on NW-N-NE-E-SE aspects in near treeline terrain.

  Slopes near ridgetops in the immediate vicinity of cornices and pillows of wind drifted snow are highly suspect. Recent E winds may have scoured these wind slabs slightly, but they are still plenty thick. Identify specific areas of concern and move around them with caution and an avoidance mindset. Deeper persistent slab avalanches may occur on slopes with wind drifted snow where the obvious inclination is to think wind slab, especially near treeline. Again, don't be fooled.

      Dec 27 skier triggered wind slab avalanche (D1) and Dec 26 snowmobile triggered wind slab avalanche (D2).