Central Sierra Nevada

Avalanche problems

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Air temperature inversion conditions kept temperatures well above freezing in nearly all areas above 6,500' last night. Once again, last night's refreeze had to rely solely on heat from the snowpack radiating out into the clear night sky. The thin and superficial refreeze crust that formed overnight on open slopes will quickly melt away during this morning's sunny, warm weather. The snow surface under thick forest canopy may not have refrozen last night. Wet loose avalanches will become possible in wind protected areas on all aspects as the morning progresses. Long steep slopes can produce larger wet snow avalanches, but smaller wet loose avalanches can still have consequences in areas with terrain traps like cliffs or creeks.

  The change from frozen snow to wet snow will likely happen quickly today if thicker cloud cover holds off until this afternoon as expected. Once the snow starts feeling wet and mushy, it's time to move away from avalanche terrain or move to a place where the snow surface remains colder (wind exposed slopes). Sinking into boot-top deep wet snow or triggering roller balls and pinwheels often indicate that wet loose avalanches could occur.

  

• 

  Cornices

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  The cornices hanging off many ridgelines will continue to weaken during the warm weather. Cornice failures will be possible today, but predicting exactly which cornices will fail and when remains uncertain. If someone does trigger a cornice failure, they could end up falling down a slope and getting pummeled by large cornice blocks. In some places, recent NE winds have scoured material away from the cornices; in others, they remain large and overhung. 

  Cornices often fail farther back from the edge than expected and break wider than expected. As a result, they often surprise people. If your route takes you along a corniced ridge, keep exposed rocks or trees between you and the cornice edge. Also, be wary of traveling on slopes under cornices. It's best to avoid these slopes below cornices. If you have to travel on them, spend as little time as possible doing so.