Central Sierra Nevada

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2

  Gale force SW winds combined with feet of recent storm snow has created large wind slabs. The vast majority of wind slabs exist in near treeline and above treeline areas on NW-N-NE-E-SE aspects. Wind slabs may be encountered to a lesser extent on other aspects and/or in below treeline areas. Cornices present an additional hazard and may collapse easily today.

  Significant hazard remains today on slopes below or adjacent to cornice features or wind pillows. Be conservative around these areas and keep a wide margin of safety.

• 

  Loose Dry

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2

  Significant uncertainty exists as to the ongoing instability of 2 to 4 foot thick storm slabs on top of a weak layer of surface hoar. Both natural and human triggered avalanches were fairly widespread on this weak layer two days ago. Data collection was limited yesterday due to access difficulties.

  In any areas where surface hoar remains an active weak layer, avalanche activity could occur in lower angle terrain, well below ridgetops. Many of these areas where avalanche activity already has and may continue to occur are traditionally thought of a safe terrain. Slope angle is everything with this avalanche problem. Approach NW-N-NE-E aspect terrain with cautious route-finding. If any signs of ongoing instability are encountered including recent avalanche activity, cracking, collapse, whumpfing sounds, or unstable snowpit test results, avoid exposure to avalanche terrain including low angle slopes connected to steeper terrain above.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  3

  Uncertainty remains for ongoing instability associated with a deep slab avalanche problem. The previously problematic weak layer of crust and faceted snow is now buried 4 to 12+ feet deep in Sierra Crest locations on NW-N-NE-E aspects.

  Large destructive avalanches could be created by large triggers such as cornice collapse or deeper than normal triggers such as sinking deep into the snowpack on foot or deep trenching snowmobiles. Keep in mind that the large avalanche size would be very difficult to survive due to associated trauma and/or deep burial depth. Choosing smaller simple terrain without rocks and cliffs that is not capable of producing a large avalanche is a way to help mitigate this avalanche problem.