Central Sierra Nevada

Problemi valanghivi

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  2–3

  Heavy snow and strong winds piled slabs of wind-drifted snow onto leeward aspects yesterday. Even though the winds have decreased, they remain strong enough to keep moving snow onto those slopes today. Large human-triggered wind slab avalanches several feet deep remain likely if people venture onto steep wind-loaded slopes. The largest and most unstable wind slabs will exist near and above treeline below exposed ridges, on open slopes, and in gullies on NW-N-NE-E-SE aspects. A few wind slabs may also exist in open areas below treeline. Fragile cornices have also formed above many of these slopes. 

  Blowing snow, cornices above a slope, drifted snow, and wind-created surface textures all indicate the presence of wind slabs.  Careful and conservative route plans that give wind slabs a wide berth can help avoid getting caught in a wind slab avalanche. This planning will also steer your group into more sheltered terrain where less wind-affected snow will likely exist. 

  

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Possible

  Dimensione

  1–2

  Snow levels stayed lower than expected during the storm, and more areas received more snow. Temperatures have also cooled off, allowing the wet snow to refreeze and gain strength. These factors mean that yesterday's wet snow instabilities should not remain problematic in most places today. This fact also means that some storm snow weaknesses, like a layer of graupel observed on Luther Pass yesterday, could be more widespread and will not simply refreeze as the wet snow would. While unlikely, an isolated area where the surface hoar somehow survived the storm may not be impossible either. Slabs of storm snow may still fail on these storm snow weaknesses in some places today.

  Look for signs of instability, like recent avalanches or shooting cracks/collapses in the snow. Digging into the snow to feel for different layers of storm snow and whether or not they break apart from each other easily can also help identify where weaknesses may linger. If any signs of instability or uncertainty about a slope exist, move to terrain less steep than 30° to enjoy the snow.