Central Sierra Nevada

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  2–3

  Continued gale force Southwest winds with feet of new snow has created large wind slabs and built out fragile cornices.  Most of these wind slabs will exist on NW-N-NE-E-SE aspects in near and above treeline areas.  Yesterday, touchy wind slab avalanches occurred naturally and were human triggered in multiple locations of the forecast area.   Wind slab avalanches today would be large, destructive, and could run long distances.  These wind slabs avalanches and large cornice collapses could also step down to the Dec 1 persistent weak layer causing even larger and wider avalanches.

  Travel in, near, or below avalanche terrain is not recommended.  Blowing snow and poor visibility today will make accidentally stumbling onto a dangerous wind-loaded slope or close to the edge of a cornice easier. Today is a day to avoid all avalanche terrain.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  2–3

  The Dec 1 persistent weak layer was buried 1 to 3 feet deep before this recent storm.  It mostly existed on NW-N-NE aspects at all elevations, but was also found in other locations.  It was becoming more variable throughout our forecast region with some areas gaining strength and other areas still showing loose, dry, and weak facets.  We just received a huge load on our snowpack:  2 to 4 feet of snow with up to 4'' of SWE.  This amount of additional weight is expected to overload this weak layer in many locations.  Any avalanches associated with this weak layer would be large, destructive, and not survivable.  These avalanches would break wider than expected, wrap around terrain features, and travel farther downhill than usual. They can be triggered remotely from nearby slopes or flat areas at the bottom of a slope.    

  Very dangerous avalanche conditions will exist today. The best plan is to avoid traveling in, near, or below avalanche terrain. Poor visibility and blowing snow will make seeing the terrain around you and identifying avalanche terrain even harder today.   

   

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  2–3

  Unstable storm slabs will form on all aspects in below treeline and near treeline terrain.  Rapid loading of the snowpack and intense snowfall rates could cause these layers to fail and avalanche.  Several reports of buried surface hoar have been received over the last 2 days on multiple aspects and elevations. This layer of buried surface hoar would now be buried 2-4 feet deep and would have the potential to cause large and destructive avalanches.  Avoid travel in avalanche terrain.