Central Sierra Nevada

Problèmes avalancheux

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  1

  Slabs of wind drifted snow exist on leeward aspects in near and above treeline terrain. In some places, these wind slabs may still break away from the slope in response to the additional weight of a person on the slope. The largest and most sensitive wind slabs should exist on NW-N-NE-E-SE aspects along the Sierra Crest where more new snow accumulated. In areas where less new snow fell, wind slabs should remain smaller. Some wind slab avalanches could involve enough snow to bury or injure a person. Reports of a potential surface hoar layer in the Carson Pass area mean that some of these slabs may be more fragile there. 

  Look for clues like blowing snow, cornices above a slope, drifted snow, wind created surface textures, recent wind slab avalanche activity, and cracking in drifted snow. These signs can help identify where wind slab problems exist. Use this information to create travel plans and safety margins that keep your party our of harm's way from these wind slab problems. 

  Ski cut triggered wind slab avalanche on Tallac from yesterday:

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Unlikely

  Taille

  2

  No avalanches have been reported on the Jan 4 persistent weak layer since last weekend. Despite the lack of activity snowpit tests continued to indicate weakness in this layer during the week. That data has become more variable over time with more tests producing stable results and fewer tests producing unstable results. We also did not see or receive any reports of avalanches failing on this layer during yesterday's rain/snow event that reloaded the snowpack. In general, the majority of data and observations indicate that avalanches on this layer have become unlikely on a regional scale. Some uncertainty still exists about this layer. It may not be impossible for the right trigger to find the right trigger spot or for a larger load to trigger this layer on an isolated slope. If that unlikely but not impossible scenario were to happen, the consequences would be quite serious.

  Continue to pay attention to this layer even though avalanche activity is unlikely. Look for any signs of instability associated with it like shooting cracks and unstable snowpit tests. If you have any doubts about whether or not this layer is problematic, move to a different area.