@Dtl Yes, it's an unusual pattern, and not just because it's so big. Thunderstorms usually form a line, sometimes a very thin line, along a front. As the front passes you get a burst of t-storm activity.
I've been watching this for hours and it looks like there's a "thunderstorm generator" around Detroit that just keeps cranking them out non stop for hours and they drift southeast towards West Virginia. Weird.