Oh, man, do I remember this game.
It was played in monsoon-like conditions, primarily because the weather forecast for the next day wasn’t any better and, given that the opponent was from outside the N.L. Central (the Giants), the Cubs didn’t want to have back-to-back doubleheaders the next time the Giants came to town (in those years, some outside-the-division opponents did make two trips to Wrigley).
And so they played. I located the BCB game preview for May 14, 2011, which contained this weather forecast:
Tonight: Showers and possibly a thunderstorm.