DULUTH - Enough rain fell in a six-hour period across parts of Northeastern Minnesota and Northwestern Wisconsin Monday morning that a hydrologist with the National Weather Service here says it qualifies as a 200-year event.

"They'll have some roadwork to be doing," Steve Gohde said as the intense rainfall prompted flash flood warnings, rural road closures and a swiftly swelling Nemadji River.

Three to five inches fell across parts of northern Pine, southern Carlton and Douglas counties, Gohde said, an area more prone to flash flooding due to the terrain.

Between 2 and 4 p.m. on Monday the Nemadji River had risen from six feet to 19 feet near the city of Superior, according to National Weather Service, and it was over 20 feet as heavy rain moved into the region again after 8 p.m.

The river rises in northern Pine County on its route to Lake Superior through Wisconsin, and the weather service reports the flood crest of the Nemadji won't reach Superior until Tuesday morning.

Drivers should watch for road closures and shoulder washouts in western Douglas County and to "turn around, don`t drown when encountering flooded roads," the weather service said.

The Nemadji River is especially prone to flooding due to its clay content and lack of filtration, Gohde said. It has been the source of damaging floods in 2012, 2016 and last year.

The Snake and Kettle rivers in Minnesota could also see delayed flooding, Gohde said, as water makes its way to the main stems. The Kettle had risen six feet near Willow River by 4 p.m. Monday.