With 6-8 inches of new snow falling with this last storm, winds may have created smooth, rounded pillows of wind drifted snow are forming on a variety of old snow surfaces. While initial wind-drifted avalanches will likely be shallow, there’s potential for them to step down into the deeper, more dangerous hard slab problem, 1 to 2 feet deep, on upper elevation W-N-E facing slopes. Kaufman and Debruin both observed one of these slides running near Ben Lomond yesterday.

Outside of the wind zone, sensitive new snow instabilities may exist on all aspects. Even a small loose or soft slab avalanche could run long and far on the supportable crust, especially in steep terrain where the snow surface is smooth and continuous. With the rain and snow mix that fell, expect these to be most likely in the highest, coolest terrain above snowlines that exceeded 8000' at times.

The supportability of the Christmas Eve Rain Crust (CERC) is what determines a rider’s ability to trigger a slide on the PWL right now. The problem is, its spatial variability is concerning, with some areas hosting crusts more than 10cm thick, and others have friable, thin crusts that are weakening.

In most areas, it's unlikely that you can trigger a slab avalanche on the persistent weak layer. However, if you head to higher, wind-exposed, W-N-E terrain, it's possible to trigger a large, destructive, and potentially fatal avalanche. This afternoon into this evening, we begin to add more load on top of the CERC. While the bulk of the storm will come in late tonight into tomorrow, I'm taking the day to shift my mindset and take a step back. This next series of storms through next week is forecast to add a considerable load on top of the CERC. Our uncertainty will rise with how the crust will support this additional weight as the load increases.