Though the summer solstice officially marks the start of the hottest season, we prefer to go by the opening of Rooftop Films, the long-running series that brings underground movies and bands together. The series is getting a head-start on summer this year in order to cram its excellent lineup of 40 outdoor events into the season. Tonight's kick-off party, This Is What We Mean by Short Films, begins with a set by the Pitchfork-approved foursome Cymbals Eat Guitars and continues with two hours of excellent shorts. Then everyone heads over to Fontana's (105 Eldridge Street) for an open bar, courtesy of Radeberger Brewery, until 1 a.m. Arrive early to snag a chair, or bring your own blanket and picnic.