Central Sierra Nevada

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Wind slabs remain possible today in above treeline and near treeline terrain where recent winds have drifted snow and deposited slabs in lee areas. Ridgetop winds were out of the SW during the storm and then shifted to the NE yesterday as skies cleared. NE wind speeds peaked last night. New snow on the ground was blown around and redistributed overnight. Expect to encounter a patchwork of wind scoured and wind loaded areas today.  Areas of exposed, firm rain crust may exist adjacent to 1 to 2 foot thick wind slabs.

  Use clues such as recent avalanches, cornices, wind drifts, and snow surface texture to identify where drifting snow has deposited as wind slabs. Move around these areas with caution.

  

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Storm slab instability may linger today, especially where a layer of large graupel sits on top of a rain crust at the bottom of the recent new snow. Signs of instability were noted on this layer yesterday on Andesite Peak (Donner Summit area) and a report was received of a mid slope avalanche triggered yesterday on a NNE aspect slope of adjacent Castle Peak.

  There are easy ways to gather information on the fly about the presence of this avalanche problem. Look for evidence of snow surface cracking while moving through untracked snow. Dig quick pits with your hand down to the rain crust (where present) to look for graupel on top of the crust. Consider terrain choices, opting for more conservative terrain in areas where this avalanche problem is present.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Increasing sun angles and increasing length of daylight hours are creating more critical levels of incoming solar radiation this time of year. Warming of recent new snow will make loose wet avalanches possible today. This is most likely to occur on steep sun exposed slopes near rocks and cliffbands.

  Roller balls are the precursor to loose wet avalanches. Exercise caution on steep sun exposed slopes where roller balls are present. Terrain traps such as gullies and cliffs below can greatly magnify the consequences of becoming caught in a small avalanche. Avoid exposure to downslope hazards in areas where signs of loose wet instability are present.