Central Sierra Nevada

Problemi valanghivi

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Likely

  Dimensione

  1

  Widespread rain up to 8800 ft. over the last 24 hours should have soaked more of the old loose weak facet layers that exist on many northerly aspects. In those areas, while this layer of loose snow remains wet, it remains weak. Once it refreezes it will gain strength, but refreezing does not happen instantly and it may still be some time before this wet weak layer refreezes into a rain crust. At the upper elevations, this persistent weak layer may remain dry and loose and weak. Regardless of whether this layer is wet or dry it is barely able to support the snowpack currently resting above it. Human-triggered persistent slabs will remain possible today and some human triggered persistent slabs may be likely above 9000 ft. where more new snow has accumulated during the storm. Due to all the rain-soaked snow that may be sitting above these persistent slabs, they could entrain more wet snow and have some wet slab characteristics. The persistent slab avalanches could involve enough snow to bury a person.

  Avoid steeper slopes in areas where snow surface cracking, whumpfing, and/or unstable snowpit test results are occurring. Quick hand pits remain an effective tool for seeing if a slab over weak loose snow exists. These kinds of avalanches can be triggered from connected slopes or may not release until a person has fully committed to the slope. 

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Possible

  Dimensione

  1

  Since much of the precipitation fell as rain during this storm, rain-soaked wet snow should exist on any slopes where snow coverage existed prior to this storm. Expect roller balls, pinwheels, and wet point release avalanches to remain possible until this rain-soaked snow starts to refreeze. Some of these could entrain enough snow to bury a person especially on northerly aspects where wet saturated snow exists.

  Avoiding steep slopes where wet snow exists represents the easiest way to avoid loose wet avalanches.

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Possible

  Dimensione

  1

  Strong winds and some snow accumulation likely created new wind slabs on wind-loaded slopes during this storm. Most of these wind slabs should remain small at elevations below 8800 ft. since most of the precipitation fell as rain at those elevations. Above 9000 ft. in areas where more snow fell, larger wind slabs may exist. High elevation wind-loaded terrain along the Sierra Crest in the southern part of the forecast area holds the best potential for larger wind slabs. In isolated areas, wind slabs may be on top of old near surface facets on NW-N-NE aspects.

  Look for cornice formation, blowing snow, and signs of previous blowing snow, especially along ridgelines and wind exposed areas. Use these clues to identify where wind slabs may exist and avoid those steep wind-loaded slopes.