Tornado Map Shows States Threatened by Severe Storms

A map of areas at risk of severe thunderstorms and strong tornadoes shows parts of six states are under the threat of tornadoes produced by severe thunderstorms.

The model, produced by the National Weather Service (NWS) on Wednesday, suggests that a swath of over 39,000 square miles across the northeastern Midwest has a 10 percent likelihood of being within 25 miles of a twister.

A first area of concern encompasses part of northern Illinois and Indiana, as well as southwestern Michigan. Another runs from southeastern Missouri, across southern Illinois, Indiana and northeastern Kentucky, and into southwest Ohio.

The areas under threat include the cities of Chicago in Illinois and Louisville in Kentucky, and are estimated to have a population of nearly 12.6 million people.

Under a 5 percent risk of seeing a tornado are also southeastern Wisconsin, as well as southern Michigan, southeastern Missouri and western Ohio. The area includes the highly populated cities of Indianapolis, Indiana, and Columbus and Cincinnati in Ohio.

Much of the Great Lakes and northeastern Midwest is currently under a marginal 2 percent risk of tornado-producing thunderstorms, while the mid-Atlantic into New England faces the threat of thunderstorms on Wednesday.

What Causes Tornadoes?

The NWS said that supercell storms producing tornadoes, damaging hail and high winds would move over northern Illinois on Tuesday night and into the Ohio Valley, due to an area of low pressure ahead of a cold front.

"As the surface low continues to deepen, the low-level jet will strengthen across much of eastern IL, IN, and points south, enhancing shear," it explained, with widening cyclogenesis—the circulation of air in the atmosphere—supporting "a continued, and possibly increasing, significant-tornado threat across parts of northern IL and eventually northwest IN" on Tuesday night.

"Strong tornado potential will exist with any activity remaining along or just ahead of the cold front," the weather agency added.

"The first thunderstorms will erupt along the edge of advancing warm air early Tuesday evening from northern Illinois and Indiana to southern Wisconsin and Michigan, as well as northwestern Ohio," Alyssa Glenny, a meteorologist at AccuWeather, said. She warned that the storms will rapidly become severe and increase their spread across the region.

The NWS said that the cold front will move over the east and Gulf Coast by Thursday morning and, ahead of it, temperatures are expected to warm by 10-25 degrees Fahrenheit above average for parts of the Northeast and mid-Atlantic.

Tornadoes Arrive Early

The arrival of tornadoes in the upper eastern Midwest would come early in its usual tornado season—which typically occurs in the spring in the region. However, at least one tornado has already ripped across Wisconsin this year. No tornado warnings had previously been issued for February, according to records dating back to 1986.

On average, the U.S. sees around 1,200 tornadoes a year.

In early December, at least 13 twisters powered across Tennessee, destroying properties and downing power lines. The storm also took the lives of at least two children and four adults.