^ I don't know what the policy is exactly, but I do know that the park will run most of their rides (Lightning Run doubtful) if it's just drizzling or it's moderate rain. Obviously if it thunders or lightning, they will close the rides for a certain amount of time, and if it's constant plus pouring down rain like it was for me a couple weeks ago than it's possible that they might close down the park.
The water at the waterpark has really warmed up with this hot summer... Nothing to worry about there, it's fine after a few minutes and most of the time at the park you'd rather be in the water than out of it.