Above is a video update of the blizzard in Mt. Shasta, CA from earlier today. Dean has reported over 2 feet of snow in the city of Mt. Shasta, with over a foot of new snow since last night from the convective precipitation that has been moving through with the very cold air aloft. Under the most intense convective cells, over 2-3 inch per hour snowfall rates have occurred at Dean's location, with even higher rates further south along the Sierra, where several cloud-to-ground lightning strokes have occurred!

While the snow yesterday and before was due primarily to warm advection at low-levels ahead of the cold front and positive vorticity (spin) advection at upper levels ahead of the main vort max currently moving onshore in British Columbia, the snow today is due to almost entirely to cold advection at upper levels -- which is resulting in the development of intense convective cells. There are two primary mechanisms that contribute to the development of convective instability: warm advection at low-levels and cold advection at upper levels...For deep convection, the latter is vital! The RUC analysis below from around 2100 UTC shows that temperatures at 500 mb over northern California are colder than -30 deg C! This cold air aloft is generating major convective instability over CA, especially over the relatively warm Pacific Ocean -- and these convective elements drop extremely heavy snow as they move over the mountainous terrain. This process is very similar to the lake effect process over the Great Lakes, etc, but on a much larger spatial scale of course.

Below is a mesoscale discussion from the SPC from earlier this afternoon.