Above 8,000', areas of CONSIDERABLE avalanche danger exist both above and below treeline on NW-N-NE-E-SE aspects on slopes 32 degrees and steeper. For all other areas, avalanche danger is MODERATE on slopes 35 degrees and steeper. Wind slabs and persistent slabs can be found in a variety of areas. Natural avalanches are possible, human triggered avalanches are possible to likely.
Wind and new snow above 7,500' have combined to create wind slabs in near treeline and above treeline terrain on NW-N-NE-E-SE aspects. These wind slabs will continue to increase in size today. Human triggered wind slab avalanches large enough to bury or injure a person are possible to likely today.
Early season snowfall starting back in October allowed shallow snow cover to persist on northerly aspects above 8,000' to 9,000'. These weak layers are now experiencing rapid loading and increasing stress. The areas where the most snow existed prior to the onset of the current storm are now the most dangerous. Here in lies the issue as these same areas are the most inviting for skiing and riding today. Slope cuts and previous tracks are not reliable indications of stability when dealing with persistent slabs. The only mitigation option is terrain and/or snowpack avoidance. Either choose slopes less than 32 degrees in slope angle without steeper terrain above or avoid areas where the weak layer exists. Consciously making these types of slope scale terrain and snowpack decisions are the difference between "getting lucky" and "getting it done" in the backcountry.
The first reported avalanche of the season occurred Dec 1 in the Carson Pass area near Round Top Peak in a NNE aspect couloir at 9,800'. The triggering snowboarder was caught, carried, and managed to avoid burial or injury. Based on the report received, the suspected avalanche type is wind slab. More info is available here. Wind slabs that existed on Dec 1 prior to the onset of the current storm cycle have become larger and thicker over the past 24 hours.
Recent observations from around the forecast area have shown the presence of weak, loose grained basal facets (sugar snow) on most NW-N-NE aspects above 8,000' along the Sierra Crest and above 9,000' in the Carson Range. Snowpit tests, including those performed yesterday on Tamarack Peak (Mount Rose area) indicate that these basal facets are in poor condition to handle new snow loading. These facets will be the weak layer for persistent slab problems that exist today.
