Central Sierra Nevada

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1.5–3

  This strong atmospheric river storm is bringing heavy snow, gale force winds, and warming temperatures with rising snow levels.  2 to 3 feet of snow is expected at the higher elevations by Wednesday morning.  Gale force S-SW winds are transporting snow and creating slabs of wind blown snow along ridges, in gully features, and on open slopes.  These slabs of wind blown snow have been forming overnight with over a foot of new snow in some areas and gale force winds.  Storm slabs will become more reactive as the day progresses with warming temperatures and rising snow levels leading to heavier dense snow overloading lighter less dense snow.  Snow levels are forecasted to rise to 7500-8000' later today. 

  At higher elevations, multiple feet of heavy snow is expected.  This heavy snow could overload the previous surface rain crust that overlies weak faceted snow in mid to higher elevation locations.  Any avalanches that fail into old weak snow layers would have the potential to be much larger in size with wider propagation.  At lower elevation areas, the old surface rain crust will be an efficient bed surface for this new storm snow to run on.  As temperatures and snow levels rise through the day, storm slab avalanches could have wet snow characteristics.     

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1–2

  Widespread wet loose avalanche activity will occur as temperatures and snow levels are expected to rise to 7500-8000' today.  New snow overnight and through this morning will become deep, wet, and unstable as snow levels rise.  Roller balls, pinwheels, and much larger wet loose avalanches involving all of the new storm snow could occur on all aspects.  Wet snow problems will also extend slightly higher in elevation into areas where heavy wet snow falls instead of rain.  The surface rain crust from the last storm will be a very efficient bed surface for these wet loose avalanches to run on.