雅虎香港電視

A dark shelf cloud loomed over Arlington Heights, Illinois, during morning thunderstorms on Thursday, July 18.

The National Weather Service (NWS) reported a “significant thunderstorm risk” on Thursday as thunderstorms moved through Iowa and over Illinois. The storms were predicted to bring “damaging winds” and “localized flooding,” along with heavy rain, the NWS said.

Shelf clouds are low, horizontal-shaped clouds that form along the front edge of a thunderstorm, according to the NWS. Credit: Jake Smith via Storyful