Central Sierra Nevada

Lawinenprobleme

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–3

  Gale force South-Southwest winds will continue today forming wind slabs in near and above treeline areas.  Heavy and very dense wind slabs existed yesterday throughout the forecast region.  Another round of wind slabs will form today as this next storm impacts our area.  These wind slabs will form along ridges, in gully features, and in open areas.  Large and fragile cornices are built out along ridgelines and could collapse today.  Any large cornice collapse or large avalanche has the potential to step down into older and deeper weak layers in the snowpack creating very large avalanches.   

  Wind slab avalanches will become likely today.  Look for recent avalanche activity, blowing snow, and large cornices above a slope as clues as to where these wind slabs exist.  Avoid steep wind loaded slopes, areas below large cornices, and avalanche run out zones today.  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1.5–3

  We have been dealing with a weak upper snowpack in the majority of our forecast area that formed during our dry January.  Deeper snowpack weak layers near the ground have been isolated to the far eastern and southern portions of the forecast region where a much more shallow and weaker snowpack exists.  With incremental loading of the snowpack over the last week with multiple heavy wet storm events, these weak layers may be reaching their failure point.  Recent observations showing cracking and failures on these weak layers have become concerning. 

  As another large storm loading event begins today, large avalanches failing on persistent weak layers deeper in the snowpack will become possible.  Large loads like avalanches and cornice collapses would be the most likely triggers for today.  As this storm loads the snowpack with more weight, it's not out of the question that natural avalanche activity could occur on these weak layers during this storm.  Even with all the uncertainty, enough signs and evidence exist to take this problem seriously.  Any avalanches associated with this problem would be large and have severe consequences.