What's Causing These Thunderstorms?

The reason that these thunderstorms occurred yesterday afternoon
wasn't due a warm front or a cold front, it was actually due to a small-scale feature called a lake breeze boundary. In this case, a strong wind out of the southwest blew over the Great Lakes, dragging the cool, stable air from over Lake Erie and Ontario across the land northeast, or downwind, of the Lakes. The issue here was, the air surrounding the Lake-adjusted air was about 10-20 degrees hotter and much more unstable! Therefore, on the line between these Lake-calmed corridors of air and the unaffected, more unstable surrounding "land" air, or on the lake breeze boundaries (almost like a mini-cold front), thunderstorms popped up. On this radar image, you can best see the lines of storms popping up on the periphery Lake Erie's far northern and far southern shores and streaming off to the north and east, carried away the southwest winds. Rochester, and most of the surrounding area remained protected by a shield of more stable, modified Lake air.

Jonathan Myers