Last summer I was driving down the highway one day and saw a strange storm. The entire sky was clear, not a cloud in the entire sky except for one small cloud, maybe a mile wide (looked like 30 feet wide from the ground) and this cloud had a severe thunderstorm. It was a hot humid and windy day, but this was really weird. There were lightning bolts every few seconds, I even saw a radio tower get struck. The flashes inside the cloud were all over the sides and top. I pulled over and watched it for a while as it slowly moved across the sky. I got off the highway and went to a pharmacy to buy a disposable camera, but when I came out of the store, the storm was nowhere to be seen. I drove for miles in the direction of where I saw the cloud, and ended up finding the ground soaked from heavy rain, but no storm anywhere. The area of wet ground ended abruptly at one point where it was soaking wet with puddles everywhere, and ten feet away the ground was bone dry.
I now carry a digital video camera in my glove box just in case I see anything like this again, but I mainly use it for videoing trains.