The rapture, quickly followed by Armaggedon...
Actually, to be serious, that is thunderstorm Babs coming out of the Midwest. When Babs meets Izzie, they're going to go to Canada and get married.
Actually, there was a front along the eastern seaboard that Isabel plowed into yesterday. Referring to your graphic, you can see the front still draped around it in a a big "S" loop sweeping down around Newfoundland and up and over Isabel. It actually flattened Isabel out along one edge when it hit, and it's still protecting the southeast from Isabel's effects.
Then you can still see the other high pressure area way to the east that was guiding Isabel when it was moving due west in the mid-Atlantic.
So I think these fronts act sort of like flexible barriers.
... all observations uncertified!