Yes, the stage is covered so there usually isn't an issue for the performers.
Yes. Sat thru West Side Story a few weeks ago wearing a poncho for a while. Some people had tarps over their heads.
It can. On the website, they say to call their number to see of there is a severe weather contingency. If you are on the lawn and still want to go, I'd bring a tarp and umbrella. Someone had a tent up the other night.
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