Massive storm system threatens northwest Ohio, southeast Mich.

Weather watches and warnings in northwest Ohio and southeast Michigan.

A large portion of northwest Ohio and southeast Michigan face a moderate risk of severe weather Wednesday into Thursday morning as a massive line of storms moves through the Midwest.

The storms could affect more than one in five Americans as they roar through the nation's heartland and to the east coast, carrying hail, lightning, and damaging winds.

These storms, which could produce a derecho (massive storm of strong straight-line winds spanning at least 240 miles) or tornadic activity. The National Weather Service briefly issued a tornado warning in Seneca County early Wednesday evening. No touch downs have been reported.

A Tornado Warning is in effect for portions of Defiance, Fulton, and Henry counties until 9:45 p.m.

In the Toledo-area, heavy rain and strong winds threaten residents and property after 10 p.m. Wednesday through early morning hours of Thursday.

According to Chief Meteorologist Norm Van Ness, a Thunderstorm Watch remains until 1 a.m. for all counties in northwest Ohio and southeast Michigan. Strong to severe thunderstorms, with damaging wind and hail are expected by late evening. Heavy rains will remain overnight into Thursday.

Stay tuned to WNWO for the latest severe weather updates. You can also follow any weather developments by following @WNWOtv or @WNWOWeatherTeam on Twitter, or at WNWO's Facebook page.

(The Associated Press contributed to this article.)