Near treeline and above treeline, avalanche danger remains HIGH on NW-N-NE-E-SE aspects on slopes 32 degrees and steeper. For all other areas, avalanche danger is CONSIDERABLE on slopes 32 degrees and steeper. Wind slab, storm slab, and deep persistent slab avalanches are all possible today.
Wind slabs continue to build in size. Additional new snow and wind transport over the past 24 hours has further increased the size of already unstable wind slabs that have built over the past several days. Winds slabs 2 to 6+ feet thick now exist near treeline and above treeline on NW-N-NE-E-SE aspects. Large destructive avalanches remain possible today.
In wind protected areas near treeline and below treeline, new snow continues to load on top of weak layers of near crust facets and lower density storm snow that exist between the Jan 30 rain crust and the snow surface. Some of these avalanches could be large and destructive and occur on any aspect in near treeline or below treeline terrain.
In areas above 9,500' deep persistent slabs linger near treeline and below treeline on NW-N-NE aspects. Weak layers of well developed facets and depth hoar remain buried in the snowpack in these areas and were not destroyed by rain on January 28 and 29. The likelihood of failure of these basal facets will increase as this storm cycle progresses and additional new snow load stresses the snowpack above these weak layers. Locations that are both above 9,500' and near treeline or below treeline terrain represent only a small portion of the forecast area, keeping this problem isolated in distribution.
Observations made yesterday near the Blue Lakes Road (Carson Pass area) and below Andesite Ridge (Donner Summit area) revealed unstable wind slabs and storm slabs. Near the Blue Lakes Road, near treeline and below treeline terrain with good to moderate wind protection revealed wind slabs and storm slabs up to 1.5 feet deep with cracking occurring in response to snowmobile slope cuts. Snowpit data collected in below treeline terrain on a N aspect at 8,200' revealed very repeatable storm slab propagation. The weak layer in the snowpit data and in many other areas was lower density storm snow below higher density storm snow. Below Andesite Ridge, close to the Castle Peak Road, widespread skier triggered whumphing and cracking was observed in low angle terrain below treeline on flat to NE aspects. In both areas, all snowpack instability was observed to occur above the prominent January 30 rain crust.
