I think that you are thinking about it too much. Maybe you should try practicing qi gong during thunder and lightning, and tell us what happens.
What if for instance, your qi gong class, which is once a week, which is taught by the “great taiji master” is during a thunder/lightning storm. Would you decide not to go, or do you think once you arrived your teacher would tell you, “Go home, the weather does not permit qi gong today.”
I have also heard it is bad to practice qigong in the rain and by stagnant water,ie. lakes,ponds, etc. The ideal place is under trees and by running water(river,waterfall)on a sunny day with no inclement weather