When you do most of your flight training in Florida, you learn real quick about thunderstorms. The most interesting story I've got is heading back towards Daytona one day amongst "happy" cumulus clouds. In less that 3 minutes, one of those "happy" cu's became an "angry" cu, directly in front of us. No lie, you could literally see the thing grow and morph into a thunderstorm right before your eyes. We got a vector just as we entered the cloud and started getting ROCKED. Thankfully we exited in short order.