How can you identify the upwind side of a thunderstorm, and why should you fly there? When flying around a thunderstorm, it is advised that you fly in the upwind portion of the thunderstorm. First off, how do you figure out which side is the upwind and downwind of a thunderstorm? Second, why fly in the upwind?
The "anvil" of a Thunderstorm is always on the downwind side. Airline pilots routinely deviate around the upwind side in hopes of a smoother ride. 

photo source: CRAZY CLOUDS: The Thunderstorm Anvil