Lollapalooza opened 35 minutes late on its first day because of a potential threat for severe weather.
"Doors for Day 1 of #Lolla are delayed due to weather," Lollapalooza tweeted Thursday morning. "Stay tuned for more info."
The four-day Grant Park festival was supposed to start at 11 a.m. Gates opened at about 11:35 a.m.
Crowds of people were seen outside the gates waiting to get in.
A cold front is expected to pass through the city in the afternoon raising the possibility for scattered showers or storms developing.
The Storm Prediction Center has the Chicago area in the general risk category for storms, meaning no severe weather is initially expected but heavy downpours are possible.
Temperatures Thursday and throughout the weekend will be in the upper 70s to mid-80s.