Bridgeport Avalanche Center

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2.5

  1-2 feet of new snow has fallen in the past 24-48 hours, and along with it, strong winds from the South-Soutwest. Active wind loading was observed all day yesterday along with stormy snowy weather.  Multiple crown lines from a recent natural avalanche cycle were observed. Slopes that haven't slid naturally could be touchy and sensitive to triggering. Pay attention to the obvious signs of wind-blown snow. The terrain below ridges, in start zones, gullies, convexities, or slopes that collect windblown snow will be suspect today. Wind slabs sometimes have a texture on the surface and feel stiff to the hand. Wind-driven snow can sound hollow and feel firm. Outside of recent avalanche activity, shooting cracks, collapses, and whumpfing sounds are all red-flag warnings that the snow is unstable. Triggering a wind slab today could cause an avalanche to step down to deeper instabilities in the snowpack (see problem #2).  Consider terrain options that are more protected from the wind to avoid the wind slab problem. 

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–3

  Several feet of snow in the past 48 hours have fallen on top of weak older snow now buried deep in the snowpack.  Large natural and human-triggered avalanches have failed on these weak layers across the forecast region.  Reports of instability in the Virginia Lakes area such as shooting cracks, whumpfing, and collapses from the recent snow-loading event are the audible and visual red flags that speak loudly, the snow is not stable and still adjusting to the recent load. 

  Persistent Slabs are hard to predict.  The visual and audio clues that were obvious during the storm cycle might not be present today. The problem will take time to resolve and is now buried deep within the pack. You can't see this problem on the surface (like a wind slab) and the avalanches that get triggered often break larger and are more destructive than we anticipate. Terrain avoidance is the best way to mitigate this problem. North-facing terrain where faceted, surgery snow existed before the storm, along with crusts intermixed between the facets, have created a complex picture within the snowpack.