Thunderstorms are fatal, all the above avoidance advice is very good... it's quite simple really, chance your arm with a thunderstorm and you are surrendering your fate and that of your passengers to chance..do not do it. If you cannot go round the storm, turn back. If you are on the ground wanting to take off when there is a storm in the way, don't, until it is plainly safe to do so. I make no apologies for sounding high and mighty, I am a commercial pilot too, well aware of the pressures we face to get the job done. Just respect the weather for what it is; bigger than all of us. (Climbs down off soap box).