I sent out invitations for Olive's birthday party at the park, and of course the day we're supposed to have it (Sunday) there is rain forecast for the day before and it's a little chilly only on that day.

We can't just move the party some place indoors if it rains the day of because of the number of people... should I move the venue to something indoors to be on the safe side (would have to book a venue so needs to be done in advance) or hope for the best?