CHICAGO – Tens of millions of people from the Upper Midwest to the Ohio Valley are on alert as a multiday severe weather threat begins Wednesday, with forecasters warning of storms capable of producing tornadoes, large hail and damaging wind gusts.

This new threat comes after an eerie lull in extreme weather during a month that is typically bustling with severe weather.

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The FOX Forecast Center said that confidence is continuing to grow around a more active severe weather pattern starting Wednesday as an upper-level disturbance emerges from the West and moves into the central U.S.

The disturbance will then help to form a vigorous area of low pressure at the surface across the central and northern Plains, setting the stage for storms to fire up across portions of the Midwest, including cities like Chicago and Milwaukee, by late Thursday and into Thursday night.

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The FOX Forecast Center said the strongest instability and storm energy on Wednesday will be found from the Kansas–Nebraska border northward into the Dakotas.

NOAA’s Storm Prediction Center (SPC) has placed about 1.3 million people in a Level 2 threat on its 5-point severe thunderstorm risk scale.

This includes cities such as Grand Island and Kearney in Nebraska, Sioux City in Iowa, Sioux Falls in South Dakota and Bismarck in North Dakota.

Thunderstorms that develop on Wednesday will be capable of producing very large hail (potentially larger than 2 inches), damaging wind gusts and some tornadoes.

Severe storm threat grows in Chicago, Milwaukee

Forecasters have been monitoring the severe weather threat in the Midwest since the weekend, and that continues to grow.

More than 16 million people in cities like Chicago and Naperville in Illinois, Milwaukee and Madison in Wisconsin and Grand Rapids in Michigan have been placed in a Level 3 out of 5 threat on Thursday.

Cities like Detroit, Indianapolis, Minneapolis and Cincinnati are currently under a Level 2 out of 5 threat.

The FOX Forecast Center said that as the system continues to intensify, moisture from the Gulf will surge north and combine with high instability and wind shear – the change in wind speed and direction with height – to support the potentially volatile severe storm environment.

An early-morning “cap” – essentially an atmospheric lid – will erode quickly by Thursday afternoon, allowing severe storms to develop in central and southern Minnesota.

Storms will be capable of producing very large hail and damaging wind gusts. There may also be some wind shear that could produce an early tornado threat.

Ahead of that line, supercell thunderstorms could develop where wind shear is highest. The FOX Forecast Center said there is the potential to see long-lived supercell thunderstorms in portions of Illinois, northern Indiana, southwestern Wisconsin and southwestern Michigan.

Those areas, forecasters said, are where there could be a possibly significant tornado threat.

The severe weather threat will continue as we head toward the end of the workweek, with more than 18 million people in cities like St. Louis, Indianapolis, Cincinnati, and Memphis and Nashville in Tennessee in a Level 2 out of 5 risk of severe weather.

The main threats from thunderstorms that develop will be large hail and damaging wind gusts, but tornadoes will also be possible.

There’s been an eerie lull in severe weather over portions of the country recently, especially in the central U.S.

May is typically bustling with severe weather, including nearly 300 tornadoes on average for the month, after both March and April saw well above-average tornado reports.