I see you are from NY you so you might not find going to the Water Parks that chilly.
We were in WDW last year right after Thanksgiving and if my memory serves me correctly it was hight 70's/low 80's during the day. Our kids spent one day at Typhoon Lagoon and it was quite beautiful.
We are from Central MA and our kids are swimming in the lake as soon as the ice is gone and they will swim into October.