Severe thunderstorm warnings popped off in the greater Chicago area through the evening Thursday, forcing the evacuation of tens of thousands of people from the Windy City Smokeout.

The Windy City Smokeout Country Music and BBQ Festival began Thursday outside the United Center, and is set to run through Sunday. Around 7:20 p.m. Thursday, everyone had to leave as severe storms blew in.

Kiera Kalinowski and Ella Pignotti came to the Windy City Smokeout with boots made for walking — to paraphrase Nancy Sinatra — but they were not exactly made for what Mother Nature had in store.

"We're having like weather warnings on their like screens," said Kalinowski.

The women added that headliner Koe Wetzel finished early because of the rain.

After an afternoon of artists taking the stage, tens of thousands of people were told to evacuate as the festival was put on a delay around 7:30 p.m. before headliner Bailey Zimmerman. While most were seen rushing out to find shelter, some came prepared.

"Someone actually asked us, 'How did you know it was going to rain?,'" said April Mahy, who was part of a group clad in plastic ponchsos. "You know there's these things called the weather apps and TV!"

Rich Guidice was previously in charge of Chicago's Office of Emergency Management and Communications, which prepares for large events across the city.

"For these outdoor festivals, it's important that you highlight, and you know, you recognize hard structures in the area that you can evacuate people to if needed," Guidice said.

He, along with festival organizers, said the Malcolm X College parking garage near the United Center was where everyone should go for shelter at the Windy City Smokeout.

It is up to the command unit on site to make that call.

"When you get to that 30-mile radius or 30-mile zone, so to speak, when you notice the heavy rains, when you notice the lightning coming, that's when you have to make those decisions to evacuate," Guidice said.

A festival spokesperson said safety updates were sent through the official Smokeout app, social media, and onsite screens. It is all part of the evacuation plan made months ago.

As for everyone heading to the festival the rest of the weekend, they hope the rain will stay away.

"It's worth it to see these people, but also getting rained on is like not the best experience," said Kalinowski.

The festival did later resume, and Zimmerman took the stage.

Meanwhile, storms are also expected on Friday, and the same plan does stand.

CBS News Chicago spoke with people who said they came to the festival last year, and rain tends always to be a factor.

• Severe Weather