Moderate avalanche danger exists on all aspects and elevations through the morning hours. As the incoming storm intensifies by mid day, avalanche danger will rise to considerable. Wind slabs will develop on NW-N-NE-E-SE aspects near and above treeline and persistent slabs will be possible on N-NE-E aspects near treeline and below treeline on slopes 32 degrees or steeper. Natural avalanche activity will become possible this afternoon with human triggered avalanche activity possible to likely all day.
New wind slabs will begin forming this morning as our next storm approaches with SW gale force winds gusting over 100mph along the Sierra Crest. These wind slabs could exist on NW-N-NE-E-SE aspects near and above treeline. Look for areas of blowing snow, cornice formations, wind pillows and snow surface clues as to where these wind slabs may exist.
Persistent weak layers of buried surface hoar exist 1-3.5' deep below the snow surface. These weak layers exist on some slopes throughout the forecast area on N-NE-E aspects near and below treeline and potentially in isolated areas on NW and SE aspects. Avalanche activity has continued to occur on these weak layers over the last 2 weeks. Many slopes have already avalanched, or the buried surface hoar has been collapsed or compressed and has gained strength. In other areas, snowpack tests show that this buried surface hoar layer is still reactive.
This persistent weak layer will exist in open areas near and below treeline. The recent rain and snow is adding weight and additional stress to this layer. Avalanches associated with this buried surface hoar layer could be large, destructive and have severe consequences. Remote triggering and large propagation continues to be possible.
Observations from Silver Peak (Pole Creek area) revealed a past avalanche that was thought to have occurred either Saturday or Sunday, potentially from a rain event. This avalanche failed on the buried surface hoar layer and had an average slope angle of 30 degrees with a starting zone of 34 degrees. Multiple snowpack tests showed that the buried surface hoar was still reactive in this area and that propagation continues to be possible. A rain crust existed up to at least 8000' with 4-6'' of new storm snow on top. Warming temperatures made for sticky snow conditions below 7000' and some minor roller ball activity on solar aspects. There were no signs of instabilities associated with the wind slab or storm slab avalanche problems.
Observations from Blue Lakes (Carson Pass area) showed no signs of buried surface hoar in the area and no signs of any avalanche instabilities. There was some concern of a developing future weakness associated with the recent rain crust.
