Forecast: Storms, heavy rainfall bring flood threat in Northern MN

Heavy rainfall rates and training storms are expected to lead to localized flash flooding Tuesday afternoon, July 15, into Wednesday morning in northern Minnesota and northeast Wisconsin.

The National Weather Service in Duluth issued a flood watch, which was expanded Tuesday morning to include Carlton, southern St. Louis, southern Lake and southern Cook counties.

The agency has forecast multiple rounds of showers and storms Tuesday afternoon through the night in north-central and northeastern Minnesota, with the potential for rainfall through 7 a.m. Wednesday.

Thunderstorms are expected to redevelop and intensify along a front across east-central Minnesota into northwest Wisconsin Tuesday afternoon. These storms may be capable of producing large hail up to 1.5 inches and damaging wind gusts up to 65 mph.

Rainfall amounts of 1 to 3 inches, with heavy rates and localized areas of 4-plus inches, are expected. Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Flooding may occur in poor drainage and urban areas.

"Training" describes storm that develop and move over the same area multiple times, bringing repeated rounds of rainfall, according to the weather service. These storms increase the risk of flash flooding.

"This is usually caused by a moist air mass running into a nearly stationary front which produces persistent thunderstorm initiation," the weather service stated. "All of the Northland’s most significant flooding events have been a result of training storms."

Although an extreme example, these types of storms are what caused the extensive and destructive flash flooding in the Arrowhead in June 2024.