To tell you the truth, I usually prefer not-so-nice weather, but this is just because I like the generally short lines it produces. Most rides will stay open during the rain unless it's coming down pretty hard, with the exception of TTD (shuts down even if it's sprinkling). I'd always recommend going to the park, and really a little bit of rain does more good than harm most of the time.
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HW 2K3: 4