I was just sent this by a friend and he said it was a real-time lightning map. I looked quick and Im not sure it is up to the exact minute, but can sure give you a good idea of where thunder storms are. At least for planning a route, it could help. It is fun to watch. I need to spend a bit more time on it to see if it is accurate or not.
http://www.lightningmaps.org/realtime
http://www.lightningmaps.org/realtime