Story highlights Severe thunderstorms forced a temporary evacuation at Lollapalooza

A few performances had to be canceled

The city of Chicago extended the festival's curfew in light of the storm delay

It was a scene straight out of "The Day After Tomorrow": a sea of confused, disgruntled people flooding the streets of Chicago, left to wonder about their fate. The cause of this mayhem: severe thunderstorms, which temporarily forced the evacuation of the second day of Lollapalooza on Saturday. All was not lost, however: after a nearly three-hour delay, festival officials reopened the gates and Lolla was officially back on.

The suspension did have some irreparable effects. Several performances -- including those by Alabama Shakes, B.o.B., Temper Trap and Neon Indian -- were cancelled, and others were pushed back a few hours or shortened. There was also the reality that Grant Park was now a full-on mud bath. Still, despite being one of the most chaotic days in Lollapalooza's storied history, when Red Hot Chili Peppers took the main stage in late evening, the earlier trouble hardly mattered.

These weren't the same Chilis that last played Lollapalooza in 2006: guitarist Josh Klinghoffer was added to the mix following the departure of John Frusciante in 2009. The Anthony Kiedis-led crew delivered a set comprised largely of the classics, aside from opening with the otherworldly percussion of new tune "Monarchy of Roses" (off 2011 album I'm With You), and their trademark fusion of rock, punk and funk riffs was on full display. The setlist included everything from the melodic ("Snow (Hey Oh)," "Under the Bridge") to the mosh-pit friendly rockers ("Can't Stop") and even the Afrobeat-inspired ("Throw Away Your Television").

The city of Chicago had extended the festival's curfew in light of the day's earlier evacuation, so the band plowed on into the night, finishing their set with a two-song encore that included "Brendan's Death Song" and "Give It Away." Kiedis donned his usual attire, or lack thereof: the singer was shirtless and wore a mesh hat saluting the Los Angeles punk act OFF! Flea expressed his love for the fans and pleaded that everyone continue supporting live music "because it's all we got."

After kicking off with his monster hit "Levels," which liberally samples Etta James' "Something's Got a Hold on Me," superstar DJ Avicii shifted through a familiar formula: searing, emotional vocal samples with giant synthesizer riffs. Each track sent more young fans scrambling towards the Bud Light stage, many caked with mud. As his visuals lit up the night sky, framed by Chicago's beautiful skyscrapers, fans reacted: "Avicii is one of the hottest techno acts in the world," explained one. Another put things in perspective: "Deadmau5 is cooler, man."

Fellow EDM leader Calvin Harris inspired mud-dancing and excessive fist-pumping at Perry's Stage. "Lollapalooza, I wanna see you jump up and down," the Scottish party-starter instructed the neon-clad masses. Over the past year, Harris has been able to successfully bridge the gap between progressive house and pop music, and his Saturday set mirrored his genre-crossing: when he wasn't unleashing bass-throbbing beats during "You Used to Hold Me," the DJ was dropping the needle on his radio hits, Rihanna's "We Found Love" and his own "Feel So Close."

As Avicii and the Chilis battled it out for main-stage supremacy, Frank Ocean took to the more intimate Google Play Stage. "I see we had a little rain," the breakout R&B singer remarked, wearing his usual red and white bandana. "I'm glad you all came back." Ocean's set was an entirely suave affair: he began by sitting on a chair, serenading the adoring crowd with a cover of Sade's "By Your Side" as acoustic guitars backed him lightly. Later, thanks to his crack four-piece band, Ocean brought a heavier hand to the Channel ORANGE cut "Thinkin' Bout You" and the nostalgia, ULTRA hit "Novacane." Ocean capped his set with the gospel-tinged "Bad Religion" -- which he said spoke of his previous love affair with a man -- and the tragic epic "Pyramid."

The Weeknd, also known as the Canadian singer Abel Tesfaye, is often compared to Ocean for his floating falsetto and mysterious air. When he played the Red Bull Stage earlier in the afternoon, he peppered his set with cuts from his trio of popular mixtapes, beginning with House of Balloons in early 2011 and concluding with last December's Echoes of Silence. After a winsome "High for This," the Balloons opener and first song many heard from Tesfaye, the singer blew an adoring kiss to the crowd.

Fittingly enough, no band appeared to enjoy Lollapalooza as much as Fun. The "We Are Young" group had the unenviable task of reopening the festival post-thunderstorm and more than succeeded in the challenge. Frontman Nate Ruess, wearing neon yellow sneakers and unhinged suspenders, bounded onstage to open with "One Foot," followed it up with "Why Am I the One?" and, despite volume issues, never let up until he brought the house down with the band's breakout single.

Scottish rock band Franz Ferdinand played an expectedly energetic set that mostly stuck to the basics of mid-2000s dance-rock. Lead singer Alex Kapranos, clad in a black button-up, shook off the post-storm humidity with ease, offering career highlight tracks like "Michael" and "Take Me Out" early in the set, then tossing out a surprise cover of Donna Summer's "I Feel Love" before concluding with an impressive drum solo feature.

Twin Shadow's set was too brief -- they began nearly fifteen minutes late as they conducted an eleventh-hour soundcheck -- but what they did play was a romantic, emotionally direct show reminiscent of Eighties teen flicks. Shrouded by a smoke machine, lead singer George Lewis Jr. and his band made the most of their time with minimal stage patter that was as heart-on-sleeve as their music: "Turned out to be such a beautiful night." A set highlight was "At My Heels," for which Lewis poured genuine energy into the performance.

Star Slinger took to Perry's Stage in a blue-striped polo shirt. His performance seemed disjointed, varying between predictable and electrifying. At some points, he covered obvious tracks, including the hip-hop staple "Crossroads" by Bone Thugs N Harmony and Nicki Minaj and 2 Chainz's current hit "Beez in the Trap." He was most interesting when he invigorated the set with British rave concepts, mixing transcendent piano lines and helium vocals into his emotionally fraught atmosphere.