Severe storm, tornado and flood risk to precede cool push in midwestern US

By Renee Duff, AccuWeather meteorologist
September 20, 2018, 11:24:58 PM EDT

Ahead of a sweep of October-like air, damaging thunderstorms, including the risk of tornadoes, will march across the midwestern United States into Thursday night.

Storms have rumbled through the Midwest on a daily basis this week, producing isolated incidents of severe weather.

However, Thursday evening’s event is likely to be more robust and widespread, threatening communities from Minnesota and Wisconsin to Kansas.

The storms will feed off of unseasonable warmth and high humidity that will be drawn northward across the region.

Static Severe Upper Midwest 3 pm

“Straight-line wind gusts to 70 mph and flash flooding will be the primary threats with Thursday’s storms, though tornadoes will be possible into the early evening,” said AccuWeather Storm Warning Meteorologist Brian Koochel.

While Koochel said the greatest risk of severe weather will be from central portions of Wisconsin to southern Minnesota and Iowa, there will be an isolated risk of violent storms farther south into Nebraska and Kansas.

A small number of thunderstorms capable of producing tornadoes may also strike parts of Ohio and western Pennsylvania into Thursday night.

Minneapolis and Rochester, Minnesota; Eau Claire, La Crosse and Green Bay, Wisconsin; Des Moines, Iowa; Omaha, Nebraska; and Salina, Kansas; are among the communities that could be in the crosshairs of the storms.

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People are reminded to seek shelter indoors as soon as thunder is heard or lightning is seen.

Motorists will need to be on the lookout for roads blocked by downed trees, power lines or high water. There will be an increased risk of hydroplaning at highway speeds on interstates 29, 35, 70, 80, 90 and 94.

The corridor from southern Minnesota and northern Iowa to southern Wisconsin will face the highest risk of flash flooding due to prior downpours this week.

Static Thursday Night Downpours

To the north of the severe weather zone, a swath of drenching rain will bring a localized flood threat from the Dakotas to the Upper Peninsula of Michigan.

Part of this swath could use a thorough soaking due to ongoing drought.

As the soaking rain moves into central Ontario and the severe weather threat wanes prior to reaching Lake Michigan and the mid-Mississippi Valley on Thursday night, focus will then shift to the Northeast at the end of the week.

Koochel expects another round of severe weather to fire up on Friday afternoon across the eastern Great Lakes, western New England and part of the Ohio Valley.

Static Severe Friday 3 pm

Friday’s storms can contain torrential downpours and wind gusts to 60 mph, which can knock over trees and power lines.

Even a moderate wind gust of 40 mph could be enough to cause tree damage after Florence left the ground saturated early this week.

“The overall threat for tornadoes is quite low, but a couple of brief spin-ups cannot be ruled out before the sun sets,” Koochel said.

The storms will progress to the east-southeast into the evening hours, but they are expected to fall well short of reaching the major cities along the Interstate 95 corridor.

Download the free AccuWeather app to stay aware of the threat for severe weather in the coming days and throughout the fall months, which are typically an active time for severe storms.

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