People usually consider lightning as one of those phenomena that primitive people ascribed to mysterious and divine sources. Then modern man came along and taught the world that lightning is nothing of the sort. Its a purely natural phenomena that does not need God or gods in order to explain itself.
This might have been true for some primitive peoples, but it has never been true of classical philosophy. This is because the ancients and medievals taught that there are many aspects under which one single thing may be considered.
This is to say that lightning is caused by everything that the scientists say causes it, but the scientist cannot explain causation as such. God is what necessarily follows from any investigation into what causes anything to be at all. So God is the ultimate explanation of all things caused only if they happen to be caused. This is why, in a sense, I can answer "God" to the question "What is the cause of _____?" Not because I deny the natural causes of lightning, wind, fire, etc., but because as long as a thing is caused God is its ultimate explanation.
God causes lightning.