The alert came during the INDYCAR race. The spectators were forced to evacuate the area quickly. Photos and videos posted online showed dark, rotating clouds over the racetrack.
FOX Weather confirmed tornado sirens were activated at the venue. There were also reports of a tornado which was seen on the ground near the track.
Storm chaser Reed Timmer also warned of a "double-barreled bow echo" system heading toward Dubuque.