Central Sierra Nevada

Problèmes avalancheux

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Likely

  Taille

  1

  Gale force SW winds yesterday and overnight during the storm have created sensitive wind slabs on NW-N-NE-E-SE aspects in near and above treeline terrain.  These wind slabs will remain sensitive today to triggering and will be capable of being large enough to bury a backcountry user (size D2).  Winds will shift to the NW today and then to the NE this evening and be in the moderate to strong range.  With snow available for transport, expect wind slabs to form on SE-S-SW-W-NW aspects in near and above treeline terrain today and tonight.

  Look for blowing snow, cornice formation, wind pillows, and previous signs of snow transport.  Avoid steep wind loaded terrain and areas with large cornices overhead. 

• 

  Loose Dry

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  1

  Storm slab avalanches will be possible on all aspects in near and below treeline terrain.  These storm slabs could fail on weaknesses that formed during the storm or at the old snow/new snow interface.  Many locations above 7000' received well over a foot of new snow overnight with some areas receiving closer to 2'.

  Look for cracking or collapsing within the recent storm snow.  Hand pits are an effective and manageable tool to look for storm snow weaknesses.  Avoid areas that show signs of instabilities.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  3

  Deep slab avalanches will remain possible today on NW-N-NE-E aspects in above and below treeline terrain.  The buried surface hoar layer and facet/crust layer are now buried 4-7'+ deep in the snowpack with some shallow snowpack areas having the weak layers being 2-3' deep.  Uncertainty continues about these layers and their reactivity.  Human triggering this deep of a weak layer remains difficult, but the consequences of an avalanche remain very high.

  Managing terrain and limiting exposure continue to be the best practices for backcountry travel with a deep slab avalanche problem.  Avoid complex terrain with multiple run out zones, areas with many trigger points like cliffs/rocks, and terrain with large overhead hazards.