Central Sierra Nevada

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  A persistent slab avalanche was reported yesterday from Powderhouse Peak in the Luther Pass area.  Limited information exists at this point, but the avalanche occurred around 8800' on a N-NE aspect with wide propagation.  It had been 2 days since multiple persistent slab avalanches were last reported on Friday Feb 14.  A layer of buried surface hoar and facets continue to exist below 2 to 4 feet of recent storm snow.  Reports of signs of instabilities, whumpfing sounds and collapsing, have been decreasing over the last couple days along with snowpack tests showing this layer gaining strength and bonding into the existing snowpack in many areas.  Another large persistent slab avalanche yesterday confirms that the snowpack does not stabilize at the same rate in all locations.   While this layer is becoming stubborn and harder to trigger, large persistent slab avalanches with severe consequences remain possible.

  It is going to take time for this persistent slab avalanche problem to fully go away.  To avoid this avalanche problem, travel on SE-S-SW aspects where this avalanche problem does not exist or on sub 30 degree terrain with no other steeper connected terrain above or to the side.  If traveling in areas where this problem may exist- reduce exposure by traveling one at a time, limit time in avalanche terrain, and regroup in safe zones in the event of a large and unexpected avalanche.    

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–1.5

  Mostly sunny skies and warmer temperatures will form wet snow as daytime warming occurs.  A warming event on Sunday formed melt freeze crusts, tree bombs, and small roller balls on the snow surface up to at least 8500' on most aspects.   Additional wet snow formation is expected today with warmer temperatures and light winds.  As daytime warming occurs today, expect roller balls and pinwheels with the possibility of larger wet loose avalanches.  If the snowpack becomes deep and wet, move away from avalanche terrain or to a different aspect.