Midwest Faces Tornadoes and Strong Winds on Wednesday

Millions of people across the Midwest are at risk of severe weather on Wednesday, with forecasters warning of the possibility of intense tornadoes, damaging wind gusts and hail as large as tennis balls.

The Storm Prediction Center said areas stretching from Kansas, Missouri and Iowa east into Michigan and Ohio — including Chicago, Indianapolis and St. Louis — are at risk. The highest level of concern is focused over portions of north central Illinois and northern Indiana.

But forecasters said on Wednesday morning that there was still uncertainty over how, exactly, the day would unfold. Andrew Lyons, a meteorologist at the Storm Prediction Center, said storms already moving across parts of Iowa and Illinois were being monitored closely because how they developed would determine the location and intensity of any storms later in the day.

“This is a very complicated forecast,” he said. “This morning’s storms could potentially stabilize the environment before the second round of storms develops this afternoon, so that could shift the area of storms farther south, and tornado potential could also become limited.”

While the tornado threat remains less certain, Mr. Lyons added that widespread damaging winds are “the threat we’re most certain about,” as well as large hailstones.

The wind was already evident during the early morning storms in Iowa and Illinois. Before midday, there were more than 25 preliminary wind reports that had damaged trees and power lines across the region. The Storm Prediction Center said significant wind gusts over 80 miles per hour had already been recoded before sunrise, including a wind gust of 94 m.p.h. in Marshall County, Iowa.

Heavy rain could bring further hazards. The Weather Prediction Center has highlighted much of the Midwest as being at a risk of flash floods through Wednesday, especially in the Chicago metro area and surrounding parts of Northern Illinois into northern Indiana and southern Michigan. Forecasters said multiple rounds of rain are likely through the region, with some storms producing rainfall of up to two inches per hour. While the storms are expected to move through relatively quickly, flash flooding remains possible, especially in urban areas, where soils are already saturated from recent heavy rain.

Here’s what to expect on Wednesday:

Threat area: Iowa, Missouri, Illinois, Indiana and Ohio are at a high risk of severe weather, with the greatest concern focused on areas of north central Illinois into northwest Indiana.
Timing: Some thunderstorms may hit during the morning, especially across parts of Iowa and Illinois, before additional storms form late in the afternoon. Mr. Lyons said these early storms could influence the atmosphere and in turn affect where the greatest tornado threat eventually develops later in the day.

Through the evening and overnight, this line of storms is expected to push eastward across portions of Illinois, Indiana and surrounding areas.

Tornadoes: The strongest and most intense tornadoes are expected across areas of north central Illinois and into northwest Indiana, though Mr. Lyons said this detail could change depending on the evolution of storms earlier in the day. A lower but still notable threat for tornadoes extends into northwest Ohio and far southern Michigan.
Winds: Damaging winds are expected to be a widespread threat. Gusts could exceed 75 miles per hour, strong enough to bring down trees and power lines, as well as to cause damage to buildings.
Large hail: The largest hailstones could reach up to 2.5 inches in diameter, roughly the size of a tennis ball. The areas most likely to experience the largest hail include Missouri, Illinois and Indiana.

Wednesday’s storms were expected in some of the same areas that were hit by damaging winds and tornadoes during an outbreak last week. On June 10, a line of thunderstorms produced a derecho, winds that can be as destructive as a tornado but that move in a straight line instead of a rotation. Wind gusts up to 85 m.p.h. led to widespread damage across Northern Illinois.

The next day brought more storms and at least 20 confirmed tornadoes to the same region. At least two of the tornadoes — one in Streator, Ill., and another in Hebron, Ind. — were rated a three on the five-point enhanced Fujita tornado scale. A storm that day also toppled what is believed to have been the last surviving “witness tree” at Abraham Lincoln’s former home in Springfield, Ill.

The severe weather threat in the region is expected to be short-lived. By Thursday, Mr. Lyons said, the Northeast and the Mid-Atlantic could see some severe weather, though the storms were not expected to be as severe.

This is the time of year for severe storms

Forecasters often know up to a week in advance whether conditions are likely to be favorable for thunderstorms, but their ability to pinpoint exactly where and when those thunderstorms kick off is much more limited. Read more about why forecasting thunderstorms is still so hard.

Scientists have been able to draw links between a warming planet and many types of extreme weather, including hurricanes, heat waves and droughts. But they are not yet able to determine whether there is a link between climate change and the frequency or strength of tornadoes. Read more about tornadoes and climate change here.