Rain came down fast and hard Wednesday night in Chicago, creating some hazardous situations not only for drivers, but for first responders who were busy rescuing people who were stuck in high waters.

Early Friday morning, torrential rain fell across Cook County. Multiple crashes were reported on Chicago roads and highways and thousands were left without power across the Chicago area.

The National Weather Service issued a flash flood warning at 9:46 p.m. Tuesday night for Chicago and Cicero and the situation quickly escalated.

Chicago flash flooding caused sudden road washouts, and water rescues had to be made at more than one location on the West Side.

Chicago experienced a rare, but not unprecedented, flash flood Tuesday night in what some forecasters described as a "one-in-500-year event."

Texas. North Carolina. Illinois. New Mexico. Flash flooding has surged into the spotlight in the last week with record-breaking flood events occurring nearly back-to-back across the country. Here’s why they happened now and why floods are becoming more intense.

Straighter, smoother streams flow more violently than those that meander due to a reduction in friction. Areas with steeper terrain can see water accelerate downhill at a much faster rate causing a more destructive flash flood than flatter, open areas.

Cars were stranded and submerged on highways and under viaducts in the Chicago area Tuesday night after a thunderstorm produced quick falling, “torrential rain rates,” leading to flooded basements, water rescues “life-threatening” travel conditions and more.