Central Sierra Nevada

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Areas of blowing and drifting snow became widespread yesterday as SW ridgetop winds increased.  A few small skier triggered wind slab avalanches were triggered yesterday as new wind slabs developed. Wind speeds further increased last night, with a trace to 4 inches of new snow across the forecast area. Locally deeper, cohesive slabs of wind drifted snow are expected to linger today in places where drifting snow filled in along the down wind side of ridgetops, gullies, and other terrain features on open slopes.

  Use clues such as any remaining visible blowing snow, cornices, wind drifts, snow surface texture, snow surface cracking, test slope failures, or new avalanches to identify slopes of concern. Move around these areas with caution. Opting for wind sheltered terrain below treeline reduces the risk of encountering this avalanche problem today.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–1.5

  Wet loose instability may develop as the day progresses, depending on how much and how quickly cloud cover decreases. Similar to yesterday, air temperatures are expected to warm into the mid 30s to low 40s and incoming solar radiation is significant this time of year. Anticipate some amount of developing wet snow on sun exposed slopes as well as across northerly aspects below about 7,500' or so.

  Look for signs of developing wet snow instability, such as roller balls. The ability to trigger pinwheels and/or wet snow sluffs indicate that sufficient melt exists for wet loose avalanches to occur. If signs of surface wet snow are present, consider opting for lower angle terrain.

  Incoming solar radiation and above freezing air temperatures each of the past two days lead to the formation of a crust on the snow surface. This occurred mainly in sun exposed areas below about 9,000' as well as on some lower elevation northerly aspects. Yesterday, this crust melted in response to daytime warming. A snow surface refreeze will have occurred last night.