Unusually low temperatures will plunge into the Midwest as the Northeast and Mid-Atlantic brace for severe storms.
All of the wild weather kicked off this weekend, with deadly lightning strikes and flooding.
Flash flooding over the weekend, in suburban Chicago, turned residential streets into impassable rivers.
One driver tried to cross it. Moments later , he and his son had to be rescued, after the car got stuck.
So much rain fell so quickly, it flooded basements and overwhelmed the sewer system in Burbank, Illinois.
"It came down so fast our sewer lines couldn't keep up with the water that we had. So everything just backed up on us," said Kenneth Sanders, Burbank Public Works.
Two to four inches of rainfall fell in northern Illinois. Four to six inches of rain soaked communities downstate. And more rain is in the forecast.
In Florida, the weather caused a chaotic scene at the happiest place on Earth.
About 120 passengers had to be evacuated from the monorail at Disney World after a power outage caused it to stop in its tracks, trapping passengers 30 feet in the air.
Witnesses say they saw a few bolts of lightning nearby.
Disney officials blame bad weather for the power outage.
Then, in Colorado, lightning strikes from passing storms made for dangerous conditions in the high altitudes of Rocky Mountain National Park.
"We didn't see the bolt, it was just like a white flash. Something hit me in the head. And I lost my vision and hearing for 10 seconds," said Dan Ivarson.
Two people died in as many days. Thirteen others injured.
What's next? The feeling of fall in what is normally the warmest time of the year. Unseasonably cooler temperatures are expected to sweep through the nation's heartland as the jet stream dips down farther south than usual.
That will drop normal summer temperatures some 10 to 20 degrees.