Winds have shifted back and forth several time between east and southwest/west over the past 48 hours. Areas of blowing snow have been visible above treeline at times. Recently formed wind slabs could exist on a variety of aspects above treeline and along sparsely treed ridgelines. These wind slab are likely small in size, but in isolated areas could approach 1 foot in depth.
In areas above 9,500' to 9,800', rain did not percolate full depth through the faceted old snow layers on near treeline and below treeline NW-N-NE aspects. In these upper elevation areas, problematic facet layers were not destroyed by the rain that fell in areas of relative lower elevation. Human triggered persistent slab avalanches are not impossible on slopes that represent the highest elevation near treeline and below treeline terrain within the forecast area. In these areas, weak layers of well developed facets and depth hoar exist below the overlying slab of recent new snow.
Observations made yesterday on Rubicon Peak (West Shore Tahoe area) revealed that small grains of surface hoar were buried under yesterday's snowfall. This is not a problem today, but holds the potential to become a significant weak layer in the future. The overall snowpack continues to show evidence of strength gain following the end of the last storm cycle. A very strong temperature gradient has been observed within the snowpack and very early stage near crust facets were noted on top of the rain crust on Rubicon Peak. At the time of observation, bonding of recent new snow to the rain crust below remained strong.
Things to keep an eye on: 1) Formation of a new weak layer of near crust facets on top of the rain crust, just below the overlying slab of recent new snow. 2) Location and extent of areas of surface hoar now buried under yesterdays snowfall.
If the near crust facet layer continues to form, this metamorphosis of snow crystals on the ground could create a new weak layer within the snowpack. If this were to occur, snowpack stability could begin to increase rather than continue to decrease. Slopes that were stable this past weekend could become unstable over the coming days. If the areas of surface hoar that were buried yesterday are sizable, a problematic weak layer could be in place for later snow storms, potentially at the end of this week. As you stop from time to time, scoop up the top few inches of snow and gently shake it in the palm of your hand. If you see triangular shaped, striated snow crystals mixed in with the new snow, you are in an area with buried surface hoar. Good to know for future visits.
