Wind Slabs and Upside-Down Layering on Andesite

The rain switched to snow as we drove up to Donner Summit. Numerous roller balls and wet loose sluffs had released on the steep hillsides adjacent to I80 between Truckee and Donner Summit. Strong winds and blowing snow greeted us at the trailhead. As we skinned up Andesite, we could feel today's heavy wet snow sitting on top of lighter snow from yesterday. This heavy snow broke away from the softer snow and produced minor cracking around our skis. The layer of heavy snow got less dense but deeper as the elevation increased and the cracking became more consistent. 

When we moved out of the sheltered terrain into more open areas exposed to the winds, we could see more blowing snow, newly formed cornices, and pillows of wind-drifted snow. The blowing snow also made it hard to see long distances. We stuck to low-angle terrain and avoided traveling on or below steeper terrain. We skirted around the more significant section of a test slope to approach it from the smaller low-angle side. I gave it a slight kick at the convex rollover and caused a wind slab avalanche 18 inches deep on the slope. It fractured across this test slope (about 75 ft). We continued to look at the bigger slopes near the summit of Andesite. They were wind-loaded but had not avalanched yet.

The winds on the summit remained fierce, but snowfall decreased dramatically. By the time we came back down into lower elevations around 12:30, snowfall had stopped altogether.