Inside the warm wooden walls of Radio Coffee & Beer on a mildly chilly mid-February Monday evening, a crowd is beginning to assemble as a handful of local musicians get in tune and ready to go onstage. From left to right, there’s fiddle, mandolin, guitar, bass and banjo. Get ready, folks: Bluegrass Night is about to go down.

It happens every Monday at Radio, a popular South Austin hangout that presents live music several days a week. Sometimes the music happens on the porch, alongside the spacious outdoor grounds that surround the main room. On colder days, the action moves inside, where a quality sound system ensures a pleasant listening experience.

Members of Grammy-nominated bluegrassers Wood & Wire, progressive folk outfit the Deer, veteran roots acts Asleep at the Wheel and Robert Earl Keen’s group, string-band fixtures Green Mountain Grass and Lost Pines, and various others form the core of about two dozen players you might find onstage any given week. It’s always a five-piece lineup, but with so many interchangeable pieces, you could attend for weeks and never see the same permutation.

“People always ask us, ‘What’s your band called?’ But it’s not really a band, you know,” banjo player Trevor Smith says. “We play traditional music. We just call out tunes, and each person will know a song, and if not all of us know it, then we’ll figure it out by the end. We never do rehearsal.”

The night I attended, the lineup featured Smith, guitarist Sophia Johnson, fiddler Katie Rose Cox, bassist Andrew Pressman and mandolinist Noah Jeffries (doing double duty as sound engineer). The set list jumped from a rollicking cover of The Band’s “If I Lose” to the classic fiddle tune “Blackberry Blossom” to the century-old traditional staple “New River Train.”

“It happens on a Monday when I don’t usually have another gig, so I like getting the call” to take part, English expat Johnson says between sets. Indeed, Mondays have become one of Austin’s best nights for such residency gigs, with long-running favorites including Dale Watson at the Continental Club, Elias Haslanger and James Polk’s Church on Monday at the Continental Gallery, Christine Albert’s Mystery Monday at El Mercado Backstage, Bob Schneider’s Lonelyland at the Saxon Pub, and piano man Chris Gage at Donn’s Depot.

The history: Smith, Pressman and a rotating cast of regulars from Austin’s extensive traditional-music community began Mondays at Flipnotics about a decade ago. A couple of months after Flipnotics closed in early 2014, Radio Coffee & Beer opened, immediately picking up some of the slack.

"Bringing Bluegrass Night to Radio was a no-brainer," owner Jack Wilson says. "Flipnotics had been an incubator for a huge network of South Austin musicians, cutting their teeth night after night on that tiny stage."

“It’s a much bigger gig here,” Pressman says. “Indoors can be hit or miss, but when we’re outside, it’s pretty much always packed now, which is nice.” Indeed, Bluegrass Night is popular enough with locals to have been voted Best Ongoing Music Residency at last month’s Austin Music Industry Awards.

"We are so honored to host it every week," Wilson says, "and feel like the real reward is watching the love of the music grow."

The vibe: At the mid-February show, trad-music fans of all ages enjoyed the music. A few preschool-age children danced gleefully or sat quietly and took in the music with awe up front. Another patron cradled a canine companion in her arms. As the crowd grew, bartenders encouraged everyone to take a few steps forward, keeping the line for beer and coffee customers clear.

When it’s outside, Bluegrass Night is a laid-back affair. Some attendees bring lawn chairs and blankets to watch from the front of the stage; others gather at adjacent picnic tables, grabbing a beverage from the bar or a snack from the on-site Veracruz food truck and letting the music drift their way on the breeze.

The lineups: Pressman and Smith generally plan out the players a few weeks into the future. Here’s who’s scheduled for March, when Bluegrass Night is our Austin360 Residency of the Month:

March 4 — Dennis Ludiker, fiddle; Mike McKinley, mandolin; Rob Lifford, guitar; Matt Downing, banjo; Emma Rose, bass.

March 11 — Tony Kamel, guitar; Trevor Smith, banjo; Noah Jeffries, fiddle; Jesse Dalton, bass; Kym Warner, mandolin.

March 18 — Jenn Miori Hodges, guitar; Amanda Jo Chisolm, bass; Beth Chrisman, fiddle; Matt Downing, banjo; Alex Rueb, mandolin.

March 25 — Chojo Jacques, fiddle; Sophia Johnson, guitar; Georgia Parker, bass; Noah Jeffries, mandolin; Rolf Seiker, banjo.

If you go: Music begins at 8 p.m.; the band plays for about an hour and then takes a short break, with a second set to follow. There’s no cover charge, but you can slip a few bucks in the tip jar when it’s passed around. Music is inside if the temperature’s below 60 degrees; otherwise it’s outside. Radio is at 4204 Manchaca St. (just north of Ben White), far enough out to be a good option for avoiding the South by Southwest melee in March. The main parking lot in front of the venue has just two dozen spots, but there’s a secondary lot one driveway north on Manchaca Road (turn in at the 4200 Manchaca law offices and drive around to the back). Limited street parking is available, as some blocks have neighborhood-only restrictions; check for signs. More information at radiocoffeeandbeer.com.