Central Sierra Nevada

Avalanche problems

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1

  Last night, cloud cover and SW winds kept air temperatures above freezing in most areas below about 8,000' to 8,200'. As cloud cover thins today, air temperatures will warm quickly at all elevations. The shallow recent new snow will be prone to loose wet avalanche activity today on all aspects. SW ridgetop winds may provide some convective cooling near the ridgetops with snow surface melt occurring more rapidly just a short distance downslope. Avalanche size is expected mostly at D1 with up to size D2 possible.

  It is getting later in the season and the sun angle is fairly high. It is becoming increasingly challenging to use aspect to avoid snow surface warming so slope angle is the go to strategy for reducing loose wet avalanche hazard. Pay attention to snow surface warming and the presence of rollerballs and pinwheels. Once these start to form, move to lower angle terrain. Pre plan route options that give a choice of slope angle.

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1

  Recent new snow and SW winds have created wind slabs up to a foot or so thick in near treeline and above treeline areas on NW-N-NE-E-SE aspects. These wind slabs may remain unstable today and could be made easier to trigger by rapid warming. Wind slabs could take on wet slab characteristics in some areas. Anticipate avalanche size at D1 to D2.

  Identify where wind slabs exist in avalanche terrain by looking for signs of drifted snow in the form of wind pillows, textured snow surfaces, and areas below cornices. Once the features of concern are identified, find routes around them that minimize the hazard.