We're from New England and were at the YC early in December. The weather was actually fairly warm during the day, I'd say 60's, so my kids definitely did some swimming. As much fun as the slide was though, my DS only went down it once and my DD did it a few times. They both said it was cold being out of the water and having to walk over and up the stairs. We didn't do the tubes at all either, because again, they were warmer when they were submerged in the water. If you picked the YC/BC strictly based on the pool, you probably won't get to enjoy it as much as others do in the warmer weather.
Tammi