Eastside Region

Lawinenprobleme

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Very Likely

  Größe

  1–2

  SW winds will drive new snow into leeward terrain today, making wind slab avalanches almost certain. Wind Slabs are most likely Near and Above Treeline on NW through SE slopes. However, with wind speeds up to 100 mph possible over the Sierra ridges, look for wind slabs in unexpected areas. In extreme winds, slabs form mid-slope on mountainsides rather than just below summits and ridges. They could be found in open forests and clearings Below Treeline as well. Lower elevation winds sometimes flow perpendicular or opposite to the ridgetop wind direction causing cross-loading of terrain features such as gullies and ridges. Because natural avalanches are likely today be aware of overhead hazards and avoid the tracks and runouts of avalanche paths with higher elevation start zones.

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  2–3

  Heavy snowfall and wind loading will test the strength of persistent weak layers at the base of the snowpack. Three weeks of cold clear weather in November formed a layer of faceted snow on NW through E aspects at all elevations. Subsequent storms have buried this layer 1 to 3 feet below the snow surface. Persistent Slabs can be triggered remotely from a distance, for example from flat terrain at the bottom of a steep slope. If triggered, they can propagate around terrain features that would otherwise confine new snow instabilities like storm slabs, or wind slabs creating larger-than-expected avalanches. A big loading event, like this one, is a good opportunity to step back from avalanche terrain and gain more information on the persistent weak layers from patterns in natural avalanche activity.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2

  Storm slabs form when changes in temperature or intensity of snowfall form a cohesive slab within the new snow. Snowfall rates greater than 2" per hour are forecasted for this storm and could lead to instabilities within the storm snow or at the interface between the new snow and the old snow surface. On W through SE slopes that had thin coverage and exposed anchors pre-storm, storm slabs may become a problem once the old snow surface is buried and layers of storm snow are more continuous across the terrain. The size of storm slabs is directly related to the amount of new snow that has accumulated. These avalanches will be most dangerous today on slopes that end in terrain traps where avalanching snow is confined and can cause a deeper burial.