Central Sierra Nevada

Lawinenprobleme

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Unlikely

  Größe

  1

  Below treeline and near treeline terrain that is above 8,200' on NW-N-NE-E aspects is where any lingering persistent slab instability is most likely to exist. Avalanche size could reach D2. Faceted snow that formed in the snowpack during the December dry spell is the problem. This weak layer is generally found 6 inches to 2 feet below the snow surface. During the recent storms this layer became wet in some areas and remained dry to moist in other areas, especially near and above 9,000'. Ongoing unstable snowpit test results have been observed on both wet and dry facets. Wet facets have yet to fully refreeze. Open areas below treeline and near treeline with good protection from NE winds is where the facets had become weakest prior to the last round of storms. These same areas are the focus of lingering concern for this avalanche problem.

  Keep in mind that triggering of a persistent slab avalanche could very well occur on the mid or lower portions of the slope, rather than near the top like a wind slab avalanche. Assessing the snowpack too high on the slope might cause one to miss important information.  Adjust data collection locations to meaningful areas for this specific avalanche problem, which will be different than the locally more common wind slab avalanche problem.

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Unlikely

  Größe

  1

  ENE winds last night may or may not have created some small wind slabs near and above treeline on SE-S-SW-W-NW aspects. This would have occurred through redistribution of snow on the ground. Complex terrain could have a patchwork of wind loaded and wind scoured areas on the same aspect.

  Identify signs of recently wind drifted snow and the areas of potential new wind slab formation. Consider magnified consequences from down slope hazards such as rocks, trees, cliffs, or terrain traps before writing off hazard due to expected small avalanche size.