If moods were cars, the Prairie Fire Lady Choir would have brakes suitable for NASCAR.

An indicator of how well the 40-member rock ’n’ roll-flavored vocal group balances cool, casual fun with rich emotional depth, the choir went from high- revving laughter to a muted stillness in a matter of seconds during rehearsals last week at McNally Smith College of Music in St. Paul.

The abrupt halt came as PFLC member Lisa Heyman explained the origins of a song she wrote for the choir, a mostly amateur group that has been teaching its members to express themselves over the past six months.

“I wrote this about two young people who passed away,” said Heyman, whose own kids were friends with the deceased.

Titled “Porch Light” — “I’ll leave the light on,” goes the refrain — the song would be a moving tribute in the hands of any solitary folk singer. It sparks a whole other level of emotion coming from the mouths of 40 women tenderly singing in unison.

A group that made its mark reinventing songs by Prince, Metallica, TLC and Magnetic Fields, the Prairie Lady Fire Choir is in the midst of change.

The choir started informally four years ago in the living room of 89.3 the Current DJ Jacquie Fuller (she is no longer a member), and has performed everywhere from community centers and garlic festivals to the Zombie Pub Crawl and First Avenue. On Friday, the PFLC takes over the Cedar Cultural Center to debut a batch of 14 original songs.

Titled “The Songbird Sessions,” Friday’s performance is the culmination of a series of songwriting workshops — paid for with a grant from the Metropolitan Regional Arts Council — which paired the choir’s members with popular local singer/songwriters such as Aby Wolf, Chastity Brown and Dessa.

“It’s amazing to see what can happen when everyone is on board” with an original song, said Wolf, who wrote five of PFLC’s original tunes and helped arrange and compose others. It’s quite a feat, writing for 40 singers instead of just one, she said.

“It really took me a while to tune my attention to remembering what it was like to be in a choir back in high school and junior high, and what some of those songs really sounded like and how they filled out, how different lines moved against each other.”

Watching from the wings as the troupe ran through “Porch Light” in McNally Smith’s auditorium, Wolf was beaming as she whispered, “She had never written a song before, and this is what she came up with.”

The choir member in charge of the “Songbird” project, Annette Schiebout, believes the songs that came out of the workshops were already festering below the surface.

“We had to get around the vulnerability involved with writing a song and opening yourself up creatively like that,” she said.

Other songs include Wolf’s eerie-to-elegant epic “Floodgate,” Schiebout’s would-be anthem for the group, “Not a Good Man,” and a lovely one that Leah Lemm wrote about becoming a mom, “We Can Be.”

“In the end, the songs are all very different — as diverse, really, as the choir itself,” Schiebout said.

There are actually about 60 members, but only about 40 usually perform. They range in age from 22 to mid-60s. When they’re not moonlighting with the choir, they are scientists, lawyers, stay-at-home moms, marketing professionals, massage therapists, you name it.

Only a few have been professional musicians, including jazz vocalist Bobbi Miller and singer/songwriters Niki Becker and Laura Borgendale (the latter two have since flown the coop).

“None of us were comfortable being rock stars, but we wanted to start a band,” Schiebout said.

“Our first season was maybe 10 people, and it was a matter of, ‘Do you know how to sing?’ Now, we turned away about 80 people who auditioned this year. It’s a tough competition. “

A marketing professional in the group, Kate O’Reilly, said she joined Prairie Fire in its second year for the same reason most members seek it out: “We’re people who wanted to create music in some form or fashion for a long time, but didn’t have access to do it.”

While O’Reilly was quick to deny it’s all for fun — “The rehearsals are actually pretty serious and can be intense” — there’s definitely enough fun to go around.

“At the end of the rehearsals, that’s when someone usually says, ‘Hey, we’re going to get a drink,’ ” she said. “And the nice thing is, there aren’t really any cliques within the group. It’s very open.”

And lest you think PFLC’s repertoire is as serious as many of their new original tunes turned out to be, they promise they will keep singing the standards — including their decidedly irregular mash-up of Metallica’s “Enter Sandman” with “Mr. Sandman” and a giddy wham-bam medley of Prince tunes they arranged.

“They’re sort of our own crowd-pleasers,” Schiebout said — sounding a bit like the kind of rock star the members never imagined becoming, one that’s tied to playing the hits.

chrisr@startribune.com • 612-673-4658