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

  Possible

  Dimensione

  1–2

  Slabs of wind-blown snow still exist on many near and above treeline NW-N-NE-E-SE facing slopes. Human-triggered wind slab avalanches happened yesterday and will remain possible today. While today's north winds may not get strong enough to transport much snow, they could stiffen the existing wind slabs making it easier for them to break above a person on the slope. If the north winds exceed their forecasted speeds, they could also build new wind slabs on previously scoured aspects. Some of today's wind slabs may still break wider than expected. 

  Recent avalanches, blowing snow, cracking in wind-blown snow, wind-created surface textures, and cornices above a slope can help determine where these wind slabs may exist. If you see signs of unstable wind slabs, bypass those areas for more sheltered slopes without signs of wind-loading.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Possible

  Dimensione

  1.5–2.5

  Significant uncertainty surrounds this avalanche problem stemming from variable distribution of the surface hoar layer and several other possible weak layers, including graupel and lingering storm snow weaknesses in the upper snowpack. The unseasonably cold weather has allowed these weaknesses to persist, especially on NW-N-NE aspects. Some data, like a seeming lack of avalanches failing on surface hoar since Monday, indicates that some of these layers may be adjusting to the load above them. Other data, like unstable test results on the graupel layers and human-triggered avalanches on steep N-NE-facing terrain yesterday in the Donner Summit area, indicates obvious instability. 

  With all of this uncertainty and variability, suffice it to say that these avalanches remain possible, and identifying exactly which slopes may or may not fail will be difficult. Recent avalanches, unstable snowpit test results, snow surface cracking, snowpack collapse, or whumpfing can help identify unstable snow. If you see any signs of instability or have any doubt about a slope, move to lower-angle, non-avalanche terrain that is not connected to steeper slopes.