Hi yooperfan,
My DD5 and I rode Splash twice last week as soon as the park opened. The temperature was in the mid 40's, I believe. As the dad, I protected her from the water cannon spray as best I could. She didn't get very wet, and didn't seem to mind the little bit she did. It didn't make that big a difference to me, either.
Big Thunder, being an outdoor roller coaster, was significantly colder than I initially thought. But being on the ride is like adding a 20 mph wind chill to whatever the temperature is, so that's understandable in retrospect. That didn't stop my DD5 from riding eight times, though. It's her new favorite.
Len