If you fly much in the summer, thunderstorms are a huge concern. You might want to take a look at the new Lightning detector article on Wikipedia — I started the article, but then “Pierre cb” (a meterologist from Environment Canada) came in and not only corrected some of my errors, but added his own custom-drawn diagrams showing how a developing thunderstorm shows up on weather radar during each of its stages, and why lightning often appears outside of radar returns. Consider this required reading, especially if you fly IFR in the middle latitudes during the summer and routinely bet your life on your weather radar or lightning detector.