Eastside Region

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  2–3

  Fresh, reactive, wind slab will be found on W-NW-N-NE-E-SE aspects especially at upper and mid elevations today. With ~30inches of new snow in the past 24hrs at 9000ft (Mammoth area) and another 4-10inches forecast for the day today, there will be widespread, sensitive wind slab in the mountains. Strong to extreme Southerly winds have been blowing continously throughout the storm and are projected to not let up throughout the day. These winds maintained rates of over 100mph for several hours yesterday afternoon at ridgetop with mid-slope elevations seeing continous extreme velocities as well. The significant amount of transportable snow will undoubtedly continue to build significant slabs in leeward terrain.  Areas adjacent to ridgeline, cliff bands, rock outcroppings, and roll overs are all terrain features where wind slab will occur. Travel within or underneath avalanche terrain today is not recommended. Slides could be large to very large and run long distances. Pay attention to what is above you especially with minimal visibility to reduce exposure to avalanche hazard.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1–3

  With close to 30inches of snow falling over the past 24hours, (highest in the Mammoth area), and more snow forecast for today, be aware of storm slab throughout the zone. Consider ALL ASPECTS at ALL ELEVATIONS for this problem as snowfall has been significant and uniform across the forecast zone. Travel in avalanche terrain is not recommended as this fresh snowfall will be sensitive and reactive to human trigger, especially in steeper 35+ degree terrain. Shooting cracks, audible whumpfing, and fresh fat looking slopes are signs of  storm slab.  Snowfall thus far has averaged around 20inches zone wide with Mammoth and Big Pine area recording upwards of 30inches. Multiple reports from the field yesterday all recorded an upside-down nature with initial new snow fall being lighter and subsequently being capped by denser heavier snow. In stabilty tests the denser heavier surface snow was reactive and failing within the lighter snow beneath. Overall this storm has been a wet and heavy one with a huge amount of water in it. Nearly 4 inches of snow water equivalent has been measured thus far in the Mammoth area.

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  The intense snowfall, extreme winds, and rapid loading will test the weak old snow that resides at the base of the snowpack throughout the forecast zone. This wet, heavy storm with nearly 4inches of snow water equivalent has added a huge amount of weight to the underlying weak early season snow. This storm will be a true test and hopefully will flesh out any old residual weak basal snow that wasn't already flushed out with last weeks big storm.  During this on-going storm cycle, avalanches could “step down” into old weak snow layers creating large and destructive slides. Areas of most concern are from around 9200ft to 10000ft in sheltered Northerly-Easterly terrain within trees. Weak old snow did exist widely across the landscape and these condition should still be considered on most aspects W-NW-N-NE-E-SE. Specific terrain features such as boulder fields with lots of cavities, and steep roll-overs and cliffbands are specific terrain features where old snow may have been hiding and thus providing exceptionally weak spots where this new load may trigger destructive avalanches that fail at ground level.