CHICAGO -- A powerful thunderstorm rumbled into downtown Chicago on Saturday, forcing organizers to suspend the Lollapalooza music festival for more than two hours while the tens of thousands of concertgoers took shelter in parking garages.

The festivities were halted at 3:30 p.m. after the National Weather Service issued a severe thunderstorm warning because of a line of storms that was barreling down on the city from the west.

Organizers said it was unfortunate, but that safety was paramount. The estimated 100,000 concertgoers took the evacuation order in stride, for the most part, and calmly left Grant Park for nearby underground garages that were designated evacuation centers for the sold-out three-day event, which ends Sunday.

Crowds were allowed back into the venue after the worst of the storm had passed and police and concert organizers had inspected the park for any damage. It was only last summer that storm-driven wind gusts knocked down heavy stage rigging at the state fair in neighboring Indiana, killing seven people and injuring dozens of others.

Organizers posted a reshuffled Saturday lineup that added a half-hour to the night's events, which were scheduled to culminate with the Red Hot Chili Peppers performing on the main stage.

Related on HuffPost:

PHOTOS from day one of Lollapalooza 2012. All photos by Justin Barbin unless otherwise noted.
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  • Metric

    (Photo Joseph Erbentraut/The Huffington Post)

  • SBTRKT

    (Photo Joseph Erbentraut/The Huffington Post)

  • The Head and the Heart

  • The Head and the Heart

  • The Head and the Heart

  • The Head and the Heart

  • The Head and the Heart

  • The Head and the Heart

  • The Head and the Heart

  • The Head and the Heart

  • Yo-Landi Vi$$er, Ninja

    Yo-Landi Vi$$er, left, and Ninja of Die Antwoord perform at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012. (Photo by Steve C. Mitchell/Invision/AP)

  • Yo-Landi Vi$$er, Ninja

    Yo-Landi Vi$$er, left, and Ninja of Die Antwoord perform at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012. (Photo by Steve C. Mitchell/Invision/AP)

  • Band of Skulls

    (Photo Joseph Erbentraut/The Huffington Post)

  • Michael Angelakos

    Michael Angelakos of the electro-pop band Passion Pit performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012. (Photo by Steve C. Mitchell/Invision/AP)

  • The Shins

  • The Shins

  • The Shins

  • The Shins

  • The Shins

  • The Shins

  • The Shins

  • The Shins

  • A flying pig in the audience before M83

    (Photo Joseph Erbentraut/The Huffington Post)

  • (Photo Joseph Erbentraut/The Huffington Post)

  • M83

  • M83

  • M83

  • M83

  • M83

  • NERO

    (Photo Joseph Erbentraut/The Huffington Post)

  • Ozzy Osbourne

    Ozzy Osborne of Black Sabbath performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012. (Photo by Steve C. Mitchell/Invision/AP)

  • Ozzy Osbourne

    Ozzy Osbourne of Black Sabbath performs aLollapalooza on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012. (Photo by Steve C. Mitchell/Invision/AP)

  • Rahm Emanuel introduces The Black Keys