Millions of Americans faced travel disruptions and flood alerts as fierce storms slammed the Midwest Sunday night, delaying hundreds of flights.

At Denver International Airport, harsh weather led to the cancellation of 21 flights and delays for more than 900 others, as reported by FlightAware.

Southwest Airlines logged 339 delays, United Airlines 244, and SkyWest 157.

The National Weather Service has issued flood watches and warnings across parts of Kansas, Iowa, Nebraska, Missouri, Illinois, and Wisconsin. They cautioned that following the onset of rain on Saturday, multiple periods of heavy rainfall, coupled with hail, damaging winds, and isolated tornadoes, could persist into Monday.

This alert comes on the heels of a series of at least 24 storms that battered the Upper Midwest on Saturday. Omaha, Nebraska, experienced wind gusts of 80 to 90 mph, while Milwaukee was drenched with up to a foot of rain, according to NBC News.

Milwaukee’s flood watch is set to remain in effect until 7 a.m. Monday, with the weather service cautioning that excessive rainfall could still trigger flash flooding.

Milwaukee was among the hardest-hit areas, with up to 14 inches of rain recorded by Sunday and river flooding in the vicinity, according to the National Weather Service.

The Milwaukee Fire Department reported responding to more than 600 calls for gas leaks, flooded basements, power outages, and water rescues, while crews worked to drain surface water and the Red Cross opened two city shelters for displaced residents.

“We’re still in the middle of it,” Fire Chief Aaron Lipski told reporters Sunday. “We’re still catching up right now.”

Nearly 14,000 people remained without power across Wisconsin as of Monday morning, according to PowerOutage.us.

The Brewers and Mets took the field at American Family Field while the parking lot, usually buzzing with fans, stood eerily empty and closed to traffic.

“We will not be able to guarantee parking for all fans, even those who purchased parking in advance,” the Brewers said in a statement before the game.

City officials warned residents to avoid driving or walking in the standing water.

“It remains dangerous,” the City of Milwaukee Department of Public Works said in a statement.

Milwaukee County Executive David Crowley has declared a state of emergency throughout Milwaukee County following overwhelming rainfall and widespread flooding.

“Flooding is still an active emergency situation across Milwaukee County, and we are expecting more rain today and into this evening. Our top priority is the life and safety of Milwaukee County residents,” Crowley posted on X.

“I strongly urge our residents to stay cautious, stay informed, and refrain from traveling. Check in on your neighbors and loved ones, especially older adults, and seek out emergency assistance if needed. I am thankful to our first responders, law enforcement partners, social services workers, and neighbors who are lending a helping hand during a challenging time. We will get through this together, Milwaukee.”

Wisconsin State Fair organizers canceled the final day of the event after heavy rain flooded the fairgrounds in West Allis, closing busy roadways and forcing some motorists to abandon vehicles as thousands lost power.

“We are saddened we cannot deliver this final day of the Wisconsin State Fair, but know that this is the best decision with current conditions and the forecast ahead,” organizers said in a statement.

Startling videos and images showed vehicles trapped in the floodwaters at the fair as Wisconsinites desperately tried to flee the State Fair, with their hoods and umbrellas up as they waded through four-inch-deep puddles.

“We’re going to need, possibly, some federal assistance,” he said at a Sunday briefing, adding that Wisconsin Gov. Tony Evers will also declare a state of emergency to secure federal aid.

With Post wires