Central Sierra Nevada

Problemi valanghivi

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Likely

  Dimensione

  2

  Our current snowpack remains mostly shallow, variable, with multiple layers of concern.  The Dec. 11 persistent weak layer, the Dec. 25 near crust facets, and the potential for a buried surface hoar layer represent our main concerns within the snowpack.  While yesterdays storm was less than forecasted, it still dropped heavy, wet, dense, snow on top of these potential weak layers.  As the storm ended last evening, observations are limited and it's uncertain how these weak layers have adjusted to the additional snow load.  Today is a good day to tread lightly and use simple terrain if venturing out into the backcountry.  These weak layers have already caused avalanches that were deep with wide propagation.  Avalanches today could be large in size (D2 to D3), with wide propagation, and could be remotely triggered.  

  Most avalanche accidents occur post storm when the sun comes out-like today.    If heading out, use low angle simple terrain that is not connected to steeper terrain above, below, or to the side.  Making a trip plan before you depart will help you and your group find appropriate terrain for today and more importantly- terrain that should be avoided.  Any whumpfing, cracking, slope failure, or avalanche activity will be major signs of instability.  If large avalanches due occur, they could run farther than anticipated, make sure you are not in an avalanche run out zone.  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Likely

  Dimensione

  1

  Large wind slabs formed yesterday during the storm on NW-N-NE-E-SE aspects in near and above treeline areas.  Wind slab avalanches along with fragile cornices failed easily as the storm increased intensity by midday.  SW winds have remained in the strong to gale force range throughout most of the night before decreasing early this morning.  Active wind loading would have continued in any areas that had snow available for transport.  Large fragile cornices with dense and deep wind slabs will be likely today.

  Look for active wind loading or previous signs of wind transport when traveling through the backcountry. Blowing snow, snow surface scouring, and dense snow over less dense snow will all be signs of where wind slabs could exist.  Areas below large cornices and steep terrain below ridges will be of most concern for wind slab avalanches.  Make a plan to avoid travel below or near these areas of concern.