Central Sierra Nevada

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Gale-force winds and rising snow levels today will start to build unstable slabs of storm snow on many slopes. These will start small since snowfall rates and accumulation are forecasted to remain moderate today, but they will increase in size as more snow accumulates. Avalanches will become possible today in both wind-loaded and wind-protected areas across all aspects. Unstable snow will form in areas where wind-blown snow has filled in the downwind side of ridges, gullies, and open slopes first. Larger and stiffer slabs of locally deeper storm snow will also exist in these areas. In areas sheltered from the wind, the storm slabs will be smaller and softer but might still involve enough snow to bury or injure a person in a few areas if enough new snow accumulates today. 

  Conditions will change quickly today as the storm ramps up, and maintaining awareness of the changes will be challenging.  Recent avalanches, test slope failures, or snow surface cracking indicate that unstable storm slabs exist. Be willing to step back from steep terrain and enjoy the new snow on lower-angle terrain if you see any signs of unstable snow. 

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–1.5

  As the day warms, rain may fall on new snow in areas below about 7500 ft. The rain will create wet loose snow that could slide down steep slopes as a wet loose avalanche. These avalanches could entrain enough snow to knock a person over or push them into a terrain trap that magnifies the consequences of an avalanche. On long, steep slopes, wet loose avalanches will entrain more snow as they slide downhill.

  As soon as rain falls on snow, expect unstable wet snow. Roller balls, and pinwheels can also indicate larger, wet loose avalanches may soon occur. Once it starts raining, it's time to move away from avalanche terrain onto less steep slopes.