Midwest and Plains Set for Two Days of Tornadoes, Hail and High Winds

Kathryn Piotrowski | Reuters

An estimated 30 million Americans were threatened Wednesday by the beginning of a two-day storm system expected to bring large hail, strong winds and the greatest likelihood of tornadoes anywhere in the country so far this year.

The danger zone for twisters included parts of Texas, Oklahoma, Kansas and Missouri, where the worst storms were expected to form during the evening and night.

On Thursday, the highest danger is expected to shift east, toward Chicago, St. Louis and the Great Lakes.

Read more from NBC News:

Michael Slager charged with Murder of Walter Scott
In Palm Springs, America's 'oasis' grapples with drought
MH370: 60 percent of Indian Ocean search zone completed

Thunderstorms rolled through parts of Indiana and Missouri on Wednesday morning, and 2-inch hail fell on Atchison, Kansas. Hail and damaging wind was expected in the afternoon in a wider area including parts of Oklahoma and Arkansas.

"We are likely to see multiple tornadoes, and fairly strong ones as well," said Kevin Roth, a meteorologist at The Weather Channel. On both days, he said, "very large hail is possible , and we will also see some damaging straight-line winds."

The two days of forecast severe weather followed several outbreaks on Tuesday that saw flooding in St. Louis and two tornadoes in Kansas, according to the National Weather Service.

Read More Drought-parched California expecting welcome dose of spring rain