There was a really great article in OTW a while back about this subject and the author basically said that if you can see lightening even on the horizon you should get the hell out there. He had a great story about how he saw lightening in the distance and his rod starting making a weird humming sound (graphite rod I'm assuming) and he later learned that was the sound of the rod getting charged up and ready to be struck!
One time at Cutty we were out in the kayaks and a storm rolled in and there was a gaggle of babes on the beach when we got in, it was like a sign from the heavens!
