To the uninitiated, the scene might have looked like some odd mash-up of a school playground, an outdoor rave and a gallery opening. But to its many regulars, it was just another summer Saturday at MoMA PS1, the contemporary art museum in Long Island City, Queens.

For 14 years now, the museum’s courtyard has been home to Warm Up, a weekly summer event that combines experimental music, art and modern design without being as alienatingly hip as that sounds. Indeed, perhaps more than the art or the music, it is the welcoming atmosphere that draws a diverse crowd, including scores of enthusiasts who return again and again to relax, socialize and hang out for hours.

Long Island City residents are admitted free, and for many in Queens, the series has become an institution and a kind of outsourced backyard.

“It’s almost like a family,” said Rebekah Kennedy, 37, a dancer and choreographer who lives in Forest Hills, Queens, and has been attending Warm Up since it began. “We know we’re going to see each other every summer, even if we don’t see each other throughout the year.”

Word has spread widely about the series, which began last weekend and runs every Saturday through Sept. 3 from 2 to 9 p.m. A $15 ticket includes admission to the museum and access to all the outdoor activities.

“I was here almost every Warm Up last summer,” said John Bielecki, 31, a waiter and self-described body worker from Prospect Heights, Brooklyn. “This is actually the only reason I come to Queens.”

Although music may seem the dominant element, with five bands or D.J.’s scheduled each day, Warm Up is less a concert series than a street fair without the street. Vendors sell food and drink, people dance, and children frolic. But instead of browsing through T-shirts and designer knockoffs, visitors peruse the edgy contemporary art for which MoMA PS1 is known.

Dave Renard, a 35-year-old D.J., was there for the first time in part because he had friends in Zoovox, a group on the day’s bill. But he stayed because Warm Up, despite an average attendance of about 5,000 each week, was a party that he and his 1-year-old daughter, Alex, could both enjoy.

“I always looked at the lineup and wanted to come, but it seemed like it was going to be really crowded,” he said as Alex pulled on his hand, then joined the dancing. “But it’s really chill.”

Each year, the courtyard is redesigned by the winners of MoMA PS1’s Young Architects Program. “Holding Pattern,” the current exhibition, was created by Interboro Partners, an architectural firm in Brooklyn that asked local residents and organizations to suggest useful objects that it could design.

The resulting chaise longues, mirrors, tree planters, games and kiddie pools create a fun, interactive space. At summer’s end, they will be donated to the people who suggested them — small reminders of a party that reaches far beyond its place and season.