Being a Washingtonian, I have absolutely no problem being in the rain. However, most rides are in the rain - including the train (by has a small roof). The food area have covered tables and of course the market area and indoor restaurant are oerfect fine in the rain.
If the rain isn't too heavy, it should be fine with a rain coat and hood. While moving between things is open to the elements, several parts are covered. Plus the lines will be minimal.
No, there are some covered areas but you will not be able to enjoy the entire fam in a rainy day.
There are some covered areas: theater, train ride, maze. Most other rides are not covered. I'd pick a sunny day, personally...
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