Continental

Avalanche problems

• 

  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.

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Strong winds that began yesterday afternoon have been redistributing recently accumulated snow. Windslabs and deep pockets of wind drifted snow will be sensitive to human triggers. Avalanches 1-3 feet deep are likely in terrain over 30 degrees where wind transported snow has been deposited. Additional  wind transported snow may quickly add stress to windloaded slopes increasing the hazard through the day.  This problem will likely reveal itself with classic signs of instability including cracking, collapsing and recent avalanche activity.  

  Deeper avalanches (2-4 feet) will be possible where wind drifted snow is stressing buried weak layers in the snowpack (see problem 2).  

  Ice Climbers: There will be the possibility of significant overhead hazard today in many popular ice climbing areas. Windslab avalanches could sweep a climber off thier route or cause injury from falling snow.  Additional hazards may be present on access routes to climbs especially in areas that include terrain traps. Steep tight gulleys with large slopes above should be treated as hazardous today. 

   

   

   

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2–3

  We have had multiple rounds of avalanche activity associated with a weak layer of snow that is buried 2-3 feet deep in many areas. Last week several large natural avalanches that released through Thompson Pass showed this layer to be reactive and hazardous. Wind transported snow will be increasing stress on this layer today. There is quite a bit of uncertainty regarding the current senstivity of this layer but we do know that additional stress will increase the likelyhood that a human could trigger a large avalanche today. Large interconnected alpine terrain will have the possibility of producing destructive avalanches that could propagate long distances. Cautious terrain management including avoiding terrain traps and avalanche runout zones while staying off large slopes over 32 degrees is advised. Due to the depth of this weak layer signs of instability may not be present even though conditions are hazardous. 

  Triggering a sensitive windslab (problem1) could provide the stress necessary to trigger a much larger persistent slab avalanche today. 

  Ice limbers: Pay attenttion to the terrain above your climb today as well as your access routes. Large alpine slopes over 30 degrees have a weak buried weak layer that is under increased stress due to active windloading. Avoid axposure to these large slopes especially if there is a terrain trap below.