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

  3

  10 to 20 inches of new snow in the last 24 hours combined with strong southwest winds means that human triggered avalanches involving wind slabs will remain likely today. These wind slabs will exist on wind loaded N-NE-E aspects and cross loaded NW and SE aspects. Clues like blowing snow, cornices above a slope, pillows of drifted snow, and other wind created textures can help identify where these fragile wind slabs exist. Open, exposed, near and above treeline terrain will represent the most common locations for these new wind slabs, but some wind slabs could also exist on open slopes in below treeline terrain due to the strength of the winds at all elevations during this storm. Wind slabs could easily measure more than 4 ft in depth in heavily wind loaded areas and more than 3 ft in depth in almost any wind loaded area. Avalanches involving these wind slabs could easily involve enough snow to bury a person. If these wind slabs release on slopes where the persistent weak layers mentioned below exist, they could overload that deeper layer and involve even more snow. 

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Possible

  Dimensione

  2

  A persistent weak layer exists near the bottom of the snowpack on NW-N-NE aspects. So far observations and data have shown this layer is weakest on the north aspects. The additional load of new snow could be enough to push this persistent weak layer so close to the breaking point that the weight of a person on the slope could trigger a persistent slab avalanche in some areas. In many areas these persistent slabs remain confined by anchors poking through the buried weak layers that should prevent these avalanches from fracturing over large areas. However, these persistent slab avalanches could fracture across wider areas and involve much more snow on slopes with smooth ground cover and less anchors. Cracking, collapsing, whumphing, and recent avalanche activity can all provide clues as to where these persistent slabs may be an issue, but they could still occur on slopes without those clues. Digging into the snowpack to find this persistent weak layer and avoiding slopes where it exists, traveling on lower angle terrain, or traveling on well anchored terrain represents the best way to avoid this avalanche problem.