I love to go in January! It's a walk-on on all the rides, and we've been really fortunate with the temps, usually high 60's, low 70's. One year when we went in late Jan, it was 86 every day. But, I know it is often cooler, too. You kind of have to pack for a variety of temps, including coats, gloves and hats in case you need them for evenings. My kids will swim in the high 60's, low 70's, but they are definitely very chilly when not in the pool. Only one water park will be open that time of year, and I'm sure it won't be crowded!