We've gone the last 7 years for president's week. Two years were warm and sunny, two were overcast and average, one really cold, and one moderately cold and a little rainy.
You can't really predict. I will say this. If you really like to swim on vacation, swim when you can. If we get a really hot day we adjust our schedule to spend lots of time at the pool. You never know if it will stay that way for the whole trip.
We also like an afternoon break on our trips but if it's cold you'll want to stay at the parks when it's warm.
I find we change our schedule around a little more on our february trips. But on the other hand, [except for pres weekend] crowds are much lighter so it's easier to adjust on the fly.