Central Sierra Nevada

Lawinenprobleme

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1.5–2.5

  Recent storm snow was deposited on a snowpack with multiple weak layers.  Our storm snow avalanche problem has transitioned to a persistent slab avalanche problem.  Weak near surface facets formed during the multi-week dry period since the Thanksgiving holiday on northerly aspects at all elevations.  This weak layer now has up to 1 to 3 feet of new dense storm snow on top of it.  This weak sugary snow will be much less dense than the recent storm snow, potentially leading to persistent slab avalanches occurring today.

  In more isolated areas in the southern and eastern portions of the forecast region, basal facets on the ground could be reactivated by the recent storm snow.  These basal facets exist on NW-N-NE aspects above around 8000-8500', where a shallow and weaker snowpack structure formed. 

  Uncertainty exists about this avalanche problem.  Very limited information and observations have been collected since the start of the storm cycle.   These weak layers are highly variable throughout our forecast area and will gain strength at different rates.  Recent avalanches, snowpack cracking, collapsing, or whumpfing sounds will indicate that this avalanche problem is reactive in your area.  These avalanches could be large, with wide propagation, and could be remotely triggered from a distance away.  Don't let this sunny powder day lull you into complacency, large and dangerous avalanches could occur.     

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1–2

  Gale force winds yesterday created large wind slabs in near and above treeline areas. These wind slabs are expected to have formed below ridges, in gully features, and in open terrain.  Large wind slabs will remain reactive today even as winds decrease.  Where these wind slabs have formed on northerly aspects that had a layer of near surface facets, wider and larger wind slab avalanches could occur.  

  Use clues such as recent avalanches, cornice formation, new wind drifts, and snow surface cracking to identify areas of potentially unstable wind slab. Large cornices that have built out during the storm will remain weak today and could collapse with the weight of a backcountry user.  Move around these areas with caution and avoid areas below large cornices or wind loaded slopes.