Central Sierra Nevada

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–2.5

  Near and above 8000' to 8500', weak faceted snow continues to exist below our recent dense storm snow.  A persistent slab avalanche problem exists on NW-N-NE and to a lesser extent E aspects in near and below treeline areas.  This faceted snow is in the lower portion of the snowpack near the ground and around crust layers.  Recent rain has strengthened this weak layer below 8000'.  In many exposed above treeline areas, previous NE winds have scoured away this weak snow pre-storm.  Yesterday, several observations had slope scale collapses as this weak layer failed due to the weight of a skier or rider.  

  Collapses, shooting cracks, and whumping sounds will all indicate that the weak layer is active.  This avalanche problem exists in very specific terrain, with the best management technique being avoidance if traveling in these areas.  Avalanches could be triggered mid-slope or even towards the bottom of slopes, it all comes down to where the weak faceted snow exists.  Any avalanches on this weak layer could be large in size with increased consequences due to the early season conditions.  

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Strong to gale force southwest winds during the storm have built out large wind slabs in near and above treeline areas.  These wind slabs could remain problematic today on NW-N-NE-E-SE aspects along ridges, gully features, and in open areas.

  Look for cornice formation, snow surface scouring, and wind pillows as clues to where these wind slabs may have formed.  Cracking or strong over weak snow layering will indicate potential unstable wind slab.  Move around these areas of concern.