Central Sierra Nevada

Problemi valanghivi

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Possible

  Dimensione

  2–3

  Below the 2 to 4 feet of recent storm snow from last Thursday/Friday's storm, a layer of weaker less dense faceted snow exists.  Large to very large natural and human triggered avalanches have been reported failing on this weak layer since the storm began last Thursday, including an avalanche fatality on Monday February 17.  Reports of avalanches and signs of instabilities have been decreasing since the weekend along with snowpack tests showing this layer gaining strength and bonding into the existing snowpack.  The snowpack does not stabilize at the same rate in all locations and will need time for this persistent slab avalanche problem to fully go away.  While this layer is becoming more stubborn and harder to trigger, large to very large persistent slab avalanches with severe consequences remain possible.

  Managing a persistent slab avalanche problem is very challenging and requires patience.  There most likely will be limited feedback and signs of instabilities from the snowpack.  We know tracks on a slope do not indicate stability, as many of the reported avalanches had previous tracks on the slopes prior to avalanching.  High variability could exist from slope to slope, even in the same area.  As the number of avalanches decrease, the consequences of a large avalanche do not.

  To avoid this avalanche problem, travel on SE-S-SW aspects where this avalanche problem does not exist or on sub 30 degree terrain with no other steeper connected terrain above or to the side.  If traveling in areas where this problem may exist, reduce your exposure as much as possible.  Travel one at a time, limit time in avalanche terrain, and regroup in safe zones in the event of a large and unexpected avalanche.  

  

• 

  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

  Winds shifted to the East-Northeast last night and have increased in speed to the strong to gale force range.  Blowing snow and new wind slab development will occur in near and above treeline areas below ridges, in gully features and in open areas.  Look for blowing snow, new cornice features, and forming wind pillows.  Snow surface cracking in wind loaded terrain will indicate reactive wind slabs are present.  Identify where these wind slabs are forming and move around any areas of concern.