Central Sierra Nevada

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2

  Strong to gale force SW winds have continued throughout the night and into the morning.  Above 8000' where the most new snow exists, wind slabs will be likely on NW-N-NE-E-SE aspects near and above treeline.  As the winds shift to the W today, wind slabs will also be possible on cross loaded S aspects near and above treeline.  Natural avalanche activity is possible with human triggered avalanches likely above 8000', especially in the Mt. Rose area where more new storm snow exists at higher elevations.  Wind slab avalanches on NW-N-NE aspects above 9000' will have the possibility of stepping down to the deep persistent slab weak layer and causing a very large and destructive avalanche. 

  Pay attention to total snow depth in your area as new storm snow fluctuates greatly throughout the forecast area.  Look for blowing snow, cornice formation, snow surface scouring, and wind pillows to detect where wind slabs exist.  Avoid areas over 35 degrees in wind loaded terrain.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  3

  The deep persistent slab avalanche problem we have been dealing with received a very large amount of load during this storm and triggering an avalanche on this weak layer remains possible today.  The persistent weak layer is now buried anywhere from 3 to 6+ feet deep under the snow surface.  This avalanche problem exists on NW-N-NE aspects above 9000' throughout the forecast area.  These deep persistent slabs could be triggered by smaller wind slab avalanches that step down and cause failure on the persistent weak layer.  Large destructive and unsurvivable avalanches are possible today.

  Deep persistent slabs have unpredictable avalanche behavior.  These avalanches can be remotely triggered from any connected terrain.  Avalanche avoidance, cautious route finding and conservative decision making are critical today.  Avoid slopes 32 degrees and steeper and give runout zones a wider berth than normal as any avalanche may exceed path boundaries.