Eastside Region

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2.5

  Strong southwest winds caused large natural avalanches through yesterday afternoon. Northerly starting zones below ridgelines and in gullies were rapidly reloaded even after avalanches ran. Ridgetop winds shifted to the north overnight and blew snow onto sunny aspects early this morning. Wind slabs can take hours or days to stabilize. Smaller avalanches or falling cornices have the potential to step down into buried weak layers, producing even bigger avalanches that may propagate across slopes and run to valley bottoms.

  With decreasing wind speeds, we expect older slabs to slowly become more difficult to trigger. Exercise caution near ridgelines, in gullies, and on steep leeward slopes. Wind slabs may appear rounded and textured or sound hollow underfoot. Recent avalanches, shooting cracks, and collapsing in drifted snow are warning signs to dial back your slope angle and stick to wind-sheltered areas.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–4

  Many slab avalanches broke on old snow or stepped down to buried weak layers during the storm on the 7th. Several of the avalanches that broke during the past 48 hours appear to have done the same. Prior to the most recent storm, sheltered terrain, steep slopes below treeline, and areas with shallower snow depths had sugary snow at the surface or throughout the entire snowpack. The recent storm snow has made slabs thicker and potential avalanches larger. A smaller avalanche, or the weight of a person in a rocky area with shallower snow cover, could be all that’s needed to trigger an unsurvivable avalanche.

  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.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Temperatures will rise rapidly above freezing today, causing cold new snow to transition and become wet. Increasing clouds can cause a greenhouse effect, meaning that even steep, northerly slopes may develop areas of wet surface snow.

  Rollerballs and pinwheels are obvious warning signs of Wet Loose avalanches. Wet Loose avalanches can entrain heavy snow that is difficult to manage or escape from. Wet Loose avalanches can also trigger larger slab avalanches that break into deeper snow layers. The best way to manage Wet Loose avalanches is to travel when the snow surface is colder and stronger. Time your trips to avoid crossing on or under very steep slopes in the heat of the day.