With good reason, turns out that rain is a popular topic for song writers, doesn't it, Trollheart?
Well, it's "atmospheric", something everyone has experience of, and also has a sound that is tempting to incorporate into music. The Doors did it well in
Riders On The Storm, and here is a lesser known song by Dando Shaft with some fine "raining" mandolin to set the mood:-
Lyrics to show that even if people don't particularly care for the song, they can't accuse it of being off topic: