Eastside Region

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1.5–3

  Intense snowfall yesterday and strong SW winds at all elevations undoubtably led to widespread natural avalanche activity.  Even though heavy snowfall has stopped for today, moderate SW winds will continue to transport and deposit snow into sensitive Wind Slabs. Watch out for the leeward side of ridgelines, gully sidewalls and cross-slope areas of deposition where it’s likely you could trigger a large Wind Slab avalanche. Blowing snow, cornice formation, denser snow and shooting cracks are all indications of possible sensitive Wind Slabs.  Be aware of the terrain above you as Wind Slab avalanches could still release naturally today and run a long way. NW-N-E-SE facing slopes are of greatest concern at all elevations. 

  Cornices could be quite large today, give them a wide berth both from above and below. 

  Keep you and your loved ones out from under wind-loaded roof tops in town as well.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  A lot of snow fell very quickly yesterday.  Mammoth Ski Patrol reported widespread triggering of soft storm slab avalanches yesterday morning that ran quite far, even before the relentless snowfall that continued thru the afternoon. It’s still quite possible today that a rider could trigger a large soft Storm Slab Avalanche in steep terrain sheltered from the wind. Be especially careful of steep mid-slope convexities.  Watch for shooting cracks and do your own pit tests before deciding to increase the angle of slopes to ride.  Loose dry sloughing could be considerable in steep terrain as well, and could sweep you off your feet or even result in a burial especially on a slope that ends in a gully bottom. 

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2.5–3.5

  An impressive 6-10”+ of water content and many feet of snow have been added to our snowpack since last Wednesday the 22nd. While it’s our hope that all this intense loading either caused large avalanches that cleaned out the weak faceted snow near the base of our snowpack, or at least buried it so well that it is no longer sensitive to a surface trigger, we can’t be sure. 

  Mammoth ski patrol triggered very large Deep Persistent Slab avalanches failing in weak facets near the ground on Sunday with explosives. Recent reports of some very large natural avalanches in the backcountry came in with Sunday morning’s clearing as well. While it is unclear if these natural avalanches failed in old deeply buried weak layers, we certainly can’t rule out that possibility. We need a little more time for things to settle before we can say confidently that triggering a Deep Persistent Slab avalanche is unlikely. A rider hitting just the right shallow sensitive spot or the force of a smaller Wind Slab avalanche could be what it takes to trigger a failure in deeply buried weak layers near the ground resulting in an un-survivable avalanche. Steep slopes with snow cover prior to December are where this concern lies. (>~9,200’, W-N-E-SE facing).