You can’t predict the weather — or how bands mix across the 10-hour day/night of a huge rock festival on City Hall Plaza. But you can predict that Boston Calling’s here to stay, and thriving on all counts, based on Sunday’s grand finale of its third edition over the holiday weekend, with a more fab September lineup to follow.

Yes, Sunday was forecast as the poor weather day with predicted thunderstorms. However, the only downpour of the three-day fest dampened the Decemberists’ Saturday-eve slot. Sunday turned out mostly sunny and warming into the 60s for Boston Calling’s best stretch of acts, which turned out to flow remarkably well together.

Textural guitar rock ruled the mid-afternoon, a common thread varied through the ebb and flow of Kurt Vile & the Violators, Built to Split and Phosphorescent, while casual concert-goers sat and sprawled across the bricks of City Hall Plaza. Though he opened with apt gem “Wakin on a Pretty Daze,” Vile didn’t fully find his stoner-rock groove until the lurching riff of “Hunchback.” But the two-decade-seasoned Built to Spill likely surprised younger fans with its gnashing three-guitar balance, and Phosphorescent charmed, wavering with Matthew Houck’s mellow country-ish musings before peaking with the melancholy glide “Song for Zula.”

Tegan and Sara became the day’s first set where you felt the push of the 22,000-capacity crowd inside the soundboards between the alternating stages, relocated perpendicular to each other. Stages were nicely balanced visually from the foot of City Hall, particularly in VIP balconies, even if the overall flow was better with facing stages at opposite ends of the plaza before current construction on the Government Center T station.

In any case, the transition to Tegan and Sara came off less jarring than might have been expected, with Tegan and Sara Quin rocking both guitars and leather jackets with their black-clad band, conveying an austere edge much like Built to Spill.  But the twin sisters’ recent synth-pop proclivities became pronounced as the set went on, capped by their hit “Closer,” and setting the stage for the now-mainstream Bastille, which has booked its return to headline Agganis Arena on Oct. 13.

Bastille wasted no time in grabbing the masses with quaffed frontman Dan Smith leading the “Ooooah, Oooah!” chant to the title track of the fast-rising English foursome’s debut Bad Blood and bopping about in his wolf-face hoodie. The anthemic synth-rockers proved entertaining with its Coldplay-wide emoting, though Smith’s drum bashing a la Imagine Dragons grew more overwrought. Brand New followed as another veteran wild card; the alt-emo outfit elicited mixed reactions for its moody, punk-edged onslaught, which culminated in old-fashioned stage destruction, down to the toppling of an amplifier as well as using the edge of a lamp as a guitar slide.

Longtime Northwest indie-rockers Modest Mouse closed Sunday night with leader Isaac Brock passionately barking tunes from across his catalog (including favorites “Dashboard” and “Float On”) with his brashly orchestral ensemble. Given that the band hasn’t made a new album since 2007, it was amazing how fervent the young crowd was, chanting “Modest Mouse! Modest Mouse!” before the group took the stage. Then, when a U.S. Air Force horn section came out first to play the national anthem in an appropriate nod to Memorial Day, fans switched to a chant of “USA! USA!” A minute later, they were back to “Modest Mouse!” I guess that when you spend all day at a rock festival, you should know how to change gears with enthusiasm!

Speaking of which, locals Tigerman WOAH! went from an early Sunday slot before the big crowd at Boston Calling to Ned Devine’s in Faneuil Hall, to join OldJack and other Hub bands in a free club-sized complement dubbed Boston Clawing. Two stages likewise alternated to keep the music going. And when the ambitious slate of multiple short sets fell behind, Tigerman WOAH! took the practical soap-box of a second stage for a mid-point turn and, to avoid shortchanging Parlour Bells, unleashed a solitary song of shambolic hillbilly folk-punk. A lifted upright bass nearly struck a chandelier, and fans shared the mic in a rush of manic momentum, only to get “Thank you, there’s another band coming up.” Both a wicked tease and a complete statement!

There was also talk of doing Boston Clawing again in September when Boston Calling delivers its fourth edition with more diverse heavyweights that include Lorde, the Roots with Nas, the National and the Replacements (single-day tickets on sale Wednesday at 10 a.m.). The more the merrier at either end of the spectrum.