Lingering wind slabs exist in recently wind loaded areas at all elevations on NW-N-NE-E-SE aspects. Ongoing instability was observed yesterday during the late afternoon hours. Human triggered avalanches remain possible today in these areas. Areas below cornice features that receive the most direct wind loading will be the most suspect today.
Persistent slabs exist above 7,800' on NW-N-NE-E-SE aspects due the presence of a weak layer of near crust facets at the base of the recent storm snow. In some areas this weak layer is buried as little as 1.5 feet deep and in other areas is qualifies as a Deep Persistent Slab with the weak layer buried 3-4+ feet deep. Creating collapse of the weak layer is becoming increasingly difficult, especially in areas where the weak layer is buried over 3 feet deep. Large triggers such as wind slab avalanches, large cornice collapses, or multiple people on the same slope are likely required to trigger collapse in most areas. In the more isolated areas where this weak layer is less the 2 feet below the snow surface, triggering will be easier.
Observations made yesterday on Andesite Ridge (Donner Summit area) and on Stevens Peak (Carson Pass area) revealed ongoing unstable wind slabs. Recently wind loaded areas held wind slabs that contributed to a couple of isolated small natural avalanches. Skier triggered cracking was prevalent in these same recently wind loaded areas at 4 pm. On Stevens Peak a 10ft radius collapse was skier triggered on an ESE low angle feature at 9,000ft. The collapse occurred approximately 16 inches down, consistent with the depth of the near crust facet layer in that area. On the Andesite Ridge area, the near crust facet layer was observed buried over 4ft down on a minimally wind loaded NE aspect at 7,900' and was unreactive in snowpit tests.
Sun breaks today are expected to allow for short periods of rapid warming. Below average air temperatures are expected to help keep areas of wet snow instability to a minimum today. Isolated areas of roller balls and small pinwheels may occur today on all aspects as snow falls off of trees and rocks. The expected minimal amount of loose wet instability that occurs today is not expected to involve loose wet avalanches. If cloud cover decreases more than forecast or air temperatures warm more than forecast, the amount of loose wet instability will be greater than forecast.
