You've all heard the stories about movie-business veterans who can tell the total box office gross a movie will make just by looking at the amount of people queued on the opening night. For fast, colorful, summer action movies we can all play as is evident from the "Summer 2003 Movie Comparison":

From the nicely done graph it is evident that predicting final gross is a matter of simple ballistics, and final gross can be reliably guessed from first weekend gross.
Exceptions to this rule will also be genre exceptions, bringing a different audience with different behaviour to the movie theaters.