A punishing storm system tore across the Midwest and into the Appalachians this week, killing at least three people, cutting power to more than a million homes and businesses, and forcing hundreds of residents from flooded neighborhoods in Ohio and Missouri. Forecasters warn the danger isn't over: a flood watch remains in effect into Thursday morning as saturated ground braces for another round of heavy rain.

The National Weather Service says a person died in a suspected weather-related house explosion, a 4-year-old boy was killed in Indiana when a tree fell on his family's home, and another death was reported in Ohio as the storms tore through Tuesday. NBC News reported the death toll stood at three as of Tuesday, with more than a million customers left without electricity across the region.

Water Rising Fast

In Perry County, Ohio, floodwater rose 6 to 10 feet in low-lying areas, forcing roughly 200 people to leave their homes or leaving them unable to get back in, according to CNN's storm coverage. Farther south, more than 200 campers at Camp Taum Sauk in southeastern Missouri had to be rescued after 6 to 12 inches of rain fell along the Taum Sauk Reservoir in a matter of hours.

Upper Arlington Schools, just outside Columbus, canceled classes Wednesday because of storm damage, and utility crews across several states are racing to restore power before the next line of thunderstorms arrives. The same weather system produced a derecho-like line of destructive straight-line winds across the Ohio Valley and Appalachians on Tuesday, snapping trees and downing power lines from Indiana through West Virginia. Meteorologists pointed to "training" thunderstorms — repeated storm cells moving over the same corridor for hours — as the main driver behind the flash flooding in Perry County and the reservoir-fed rescues in the Missouri Ozarks.

MORE HEAVY RAIN AND SEVERE THUNDERSTORMS WILL THREATEN MANY OF THE SAME AREAS WEDNESDAY, WHERE SATURATED GROUND AND WIDESPREAD OUTAGES COULD COMPOUND THE DANGER.

The National Weather Service has extended its flood watch through Thursday morning for a wide swath of the Midwest and Mid-Atlantic, urging residents in low-lying areas to avoid driving through flooded roads and to have an evacuation plan ready. With rivers and reservoirs already swollen, officials say it won't take much additional rainfall to trigger new flash flooding before the system finally clears the region later in the week.

Utility companies in Ohio, Indiana and Missouri said Wednesday that restoring power to the hardest-hit rural areas could take days rather than hours, given the scope of downed lines and blocked roads. Local officials are asking residents who lost power to check on elderly neighbors and to avoid using generators indoors as temperatures climb into the high 80s behind the storm system.