I think the water parks close for the time it is. (And without, I also think they close earlier). The other parks at Christmas will be with more people also for the time of year. But they are very fun :)
Everything remains the same depending on the weather. On Christmas as on New Year's Eve it gets exaggeratedly full and the enjoyment is not with the same appreciation for how cornered it feels. Summer is the best option although I would prefer Spring break ...
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