Eastside Region

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1.5–3

  Over the last 36 hours, significant snowfall was accompanied by strong to extreme winds out of the south-southwest. Winds are expected to remain at transportable speeds today with another round of moderate to strong snowfall. You can expect recent deposits near and above treeline to be large as you walk out the door this morning and continue to grow in size and sensitivity throughout the day. Blowing snow and growing cornices will point to the most dangerous slopes. Stiff, textured drifts could fail naturally and break widely under ridgelines and on the sidewalls of gullies. Strong winds at all elevations could lead to some atypical loading patterns today. Don’t be surprised to find wind-stiffened surface snow in more sheltered areas below treeline. Poor visibility will make it hard to assess the terrain above you. As snowfall rates and drifting increase, avoid being on steep wind-loaded terrain and in the runouts of avalanche paths. 

  

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  10-28” of new snow has fallen over the past 36 hrs, with up to a 4-12” expected to accumulate today. Field observations yesterday noted touchy conditions with numerous natural and human-triggered soft slabs and surface sluffs. Surface instabilities, both slabs and sluffs, are expected to be reactive today in sheltered terrain near and below treeline. Winds are expected to increase at all elevations as new snow impacts the forecast area. It is possible we will see a transition today where loose sluffs become less likely as surface snow becomes more cohesive and slabs become increasingly problematic throughout the day. Convex rollovers and steep, unsupported slopes are areas to avoid.  It is also important to be aware of potential terrain traps that can increase the consequences of an avalanche. Road cuts, gully features, cliff bands, and mid-slope depressions are all places to watch for.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  A substantial load has been added to our snowpack over the last 48 hrs - over 3” of water weight in the Mammoth area and close to 1” in the Bishop area. It has been a while since we last saw avalanches breaking on weak layers buried deeply in the snowpack. However, forecasters have continued to find poor structure and propagating test results on persistent grains 3+ feet below the surface. Snowpacks do not like rapid change.  Rapid loading in the past 48 hrs and continued snow showers may be enough to stress this poor structure. While less likely than surface instabilities today, the consequences of an avalanche breaking deep in the old snow will be very high.

  Managing persistent slabs is difficult. They may be triggered remotely—from flatter terrain adjacent to steep slopes. Persistent slabs often propagate widely and in unpredictable ways. Shooting cracks and collapses are clear warning signs of the problem. However, feedback is often irregular. The best option is to minimize your exposure to steep terrain on the aspects and elevations with sugary facets buried under stiffer slabs. Use extra caution in rocky, complex terrain, near convexities, and on slopes with inconsistent snow depth.