Investigator Gary Dryfoos saw the discussion about April in Paris, and offers a non-dialectical analysis:
Well you know, the song “April in Paris” has let down a lot of tourists who find the weather kind of damp and crappy. May is much nicer, downright lovely. Lyricist E.Y. “Yip” Harburg knew this, but for him it was a matter of scansion ? “Maa-aay in Paris” just didn’t work with the tune composed by Vernon Duke. So “April” it became.
So much for climatological accuracy in music.