Winds have shifted from east to southwest over the past 24 hours. Areas of blowing snow were visible above treeline yesterday despite the forecast for light winds. Recently formed wind slabs could exist on a variety of aspects above treeline and along sparsely treed ridgelines.
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 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 near Red Lake and Elephant's Back (Carson Pass area) and near Grouse Rocks (Ward Canyon area) gave continued indications that the snowpack is continuing to gain strength. In these areas, bonding of recent new snow to the rain crust at the top of the old snow layers remained strong. This is despite a very strong temperature gradient within the snowpack that indicates the potential for a new near crust facet layer to form on top of the rain crust. Surface hoar crystals up to 1 cm in size were widespread in these areas as well.
Things to keep an eye on: 1) Formation of a new layer of near crust facets in between the rain crust and the overlying slab of recent new snow. 2) Burial and preservation of large areas of surface hoar by snow showers this week.
If the near crust facet layer forms, 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 yesterday could become unstable over the next several days. With a forecast for below average air temperatures, surface hoar might persist. If sizable areas of surface hoar are buried a problematic weak layer could be in place for later snow storms, potentially at the end of this week.
