Well, it wouldn't be such a good idea if they got caught up in a storm, would it? :p
Strong winds could blow them off-course, or even lightning has a chance of striking the hand glider, causing damage to the glider, the person, or even both.
Additionally, a weather forecast can help in my generic situations. For example, knowing whether to wrap up warm for cold weather, or wear something a bit more loose and breathable for hot weather.
