Flash flooding has inundated parts of the Midwest as heavy rainfall in half a dozen states knocked out power to thousands, forced road closures and killed at least one person over the weekend, officials said.

A person was killed in eastern Nebraska and another person was seriously injured when a tree fell on a vehicle they were in during a storm on Saturday, according to the Waterloo Volunteer Fire Department in Nebraska. The storm system produced wind gusts of up to 90 miles per hour in several Nebraskan counties, the National Weather Service said.

The National Weather Service issued flood watches and warnings for parts of Kansas, Iowa, Nebraska, Missouri, Illinois and Wisconsin. After rainfall began on Saturday in some areas, forecasters predicted “repeated rounds of heavy rain,” along with hail, damaging winds and isolated tornadoes into Monday.

Among the worst hit was the Milwaukee area, where up to 14 inches of rain had fallen in some areas by Sunday, according to the National Weather Service, which also noted river flooding in Milwaukee and Waukesha counties. Some motorists left their stranded cars on roads. Nearly 18,000 customers of We Energies in southeast Wisconsin were without power late Sunday. In the suburban village of Wauwatosa, an overflowing and fast-moving Menomonee River submerged a popular playground.