Continental

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2.5

  Strong winds redistributing surface snow will continue to be the driving force of avalanche hazard today.  Wind speeds in the 80's and gusts in the 90's were recorded on Thompson Pass in the last 24 hours.  Winds are expected to slowly decrease through the day, but remain strong enough to continue to build fresh wind slabs.  Natural avalanche activity may have peaked yesterday, but will remain a possibility today.  Expect to encounter deep wind slabs 1-3 feet on lee aspects, cross loaded gullies, terrain near ridge lines, and convex slopes.  Due to the strength of the wind, users may find wind slabs much further down from ridges than what is typical.  

  The amount of soft snow available for transport, along with the strength of winds, is enough to raise the hazard to considerable.  We also have the additional concern of a persistent weak layer being loaded (see problem 2).  There is uncertainty regarding how the sensitivity of this weak layer will react to loading and changes in the overlying slab.  Users should be aware that triggering a wind slab avalanche could step down to this layer and propagate a much larger avalanche.

  Watch for signs of instability and signs of wind loaded snow such as pillowed snow surfaces and stiffer snow at the surface.  Avoid terrain steeper than 30° where either of these are present.

   

  Ice Climbers: Today is not a good day to travel into terrain traps like Sheep and Bear creek.  There are large snow slopes above you that could fail naturally and bury you and your party.  The strength of the winds has created sensitive slabs at low elevation in some places that are large enough to knock you off your feet on even small snow slopes.  Pay attention to if snow slopes exist on your climbing route and what the overhead hazard is.

   

   

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2.5–3

  We have a known persistent weak layer that has produced human triggered avalanches at upper elevations and natural avalanches at all elevations and aspects.  This layer is under increasing stress in specific areas due to wind loading.  The slab above this layer has transitioned from ~2 feet of mostly right side up settled storm snow to variable depths of windloaded snow that is more cohesive and upside down.  Avalanches that are initiated at this layer are expected to be 2-4+ feet deep and have wide propagations.  

  Conservative terrain choices are recommended due to the combination of freshly wind loaded snow and uncertainties regarding the sensitivity of the 1/26 interface.

   

   

  

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  2.5–3.5

  A deeply buried weak layer near the ground remains a low-likelihood, high-consequence problem—especially in steep, rocky terrain and areas where the snowpack is thin or highly variable. Triggering this layer directly is unlikely at this time, but avalanches that start in the upper snowpack may step down to the basal weak layer, particularly in the Continental zone.

  Watch for thin spots near rock outcrops, scoured features, convex rollovers, and along ridge tops. Wind loading adds stress to these shallow areas, and we don’t know where the tipping point is.