I finally decided to go home and get the umbrellas that we'd forgotten, confident that this would either keep us drier or make the rain stop. Sure enough, about ten minutes after I got back with the umbrellas, it stopped raining for good.
It was a very nice display when it finally went off (after the rest of Des Plaines showed up) and included some effects I hadn't seen before. A woman sitting near us had been to the Niles display the night before and reported that this display blew Niles away.
I'm going to go take a hot shower and clean up now. :)