Hey, zoo: If you're going to cancel an event, you might want to, you know, tell someone. Before they get inside the building. There are many means of telling people something in this modern age: you can use email, phone calls, etc. or you could even put up a sign outside the building. It's raining out, and you think it's cool to let people walk all the way in before letting them know that they came in for no reason.
Not very cool, Minnesota Zoo.