If you go What: Festival on Main When: 6-10 p.m, Friday, Aug. 28 Where: Downtown Longmont, centered on Main Street between Third and Longs Peak avenues Tickets: Free Info: The Festival on Main page at downtownlongmont.com

Festival on Main is getting all grown up.

The annual event in downtown Longmont is celebrating 15 years in 2015, and organizers are treating the milestone like proud parents watching their daughter reach maturity. The festival was planned with a quinceañera theme, and it will mark a transition for the event as organizers plan to expand it in coming years.

“We’re really excited,” said Kimberlee McKee, executive director of festival organizer Longmont Downtown Development Authority. “We thought quinceañera was a good way to transition from what the festival used to be to what it can be in the future.”

The festival, set for 6-10 p.m. on Friday, Aug. 28, is centered on Main Street between Third and Longs Peak avenues. It features music, performances, art, family activities, food, craft beer and other attractions. Denver rock band Something Underground is the musical headliner, with Fort Collins alt-country band The Patti Fiasco opening.

A quinceañera is a traditional ceremony for 15-year-old girls and marks the transition to womanhood.

“The tradition is believed to have started when Spanish conquerors invaded Mexico but may date as far back as Aztecs,” according to the festival.

McKee lives near Roosevelt Park, a popular location for families taking photos of quinceañera celebrations, she said, adding, “I always thought it was really interesting.”

She also recognized how the spirit behind the tradition could be borrowed for Festival on Main. The growth of the festival, along with development of the downtown arts district, has led organizers to contemplate expanding the 2016 festival to two days and bringing it to more parts of downtown.

Expansion is afoot in other respects. The festival in past years was conceived as a community celebration, but increasingly, organizers have sought to draw visitors from outside Longmont, and that effort is reflected in the appearance on the musical lineup of artists from Denver and Fort Collins.

The quinceañera theme is in line with the festival’s goal of serving a diverse audience. It has worked with the Longmont-based radio station La Ley, which broadcasts Mexican news and music, to help get the word out to the local Latino population, and the outreach has been effective, McKee said. La Ley this year will sponsor the main stage, which features four Latin performances, a quinceañera fashion show and a piñata breaking.

A stage at Third Avenue is scheduled to showcase the year-round entertainment offered by the nearby Dickens Opera House and The Speakeasy. Comedian Michael Amaya, the family-friendly Pearl’s Treat Burlesque and musical artist beautyofmyland, from Columbus, Ohio, will be featured there.

Something Underground and The Patti Fiasco are scheduled to perform on a stage at Fourth Avenue, which is also the site of a beer garden featuring brews from the Pumphouse, Left Hand Brewing, Oskar Blues, Wibby and 300 Suns breweries.

The Left Hand Artist Group is spearheading an artist showcase at Longs Peak Avenue. Other festival attractions include dance performances, street performers, a climbing wall, an obstacle course, a bounce house, an inflatable slide, a bungee trampoline, face painters and more than 90 merchant and nonprofit booths.

Quentin Young: qyoung@aespotlight.com and twitter.com/qpyoungnews