Dangerous spring storms threaten millions in America

Millions are on alert as a severe storm system sweeps through the Ohio Valley and Northeast regions.

The Ohio Valley, middle Tennessee, and Southeast face a possible severe weather outbreak on Tuesday. Multiple rounds of storms are expected in the day. The Ohio Valley is already experiencing a storm, with 4 million people along the Ohio River under tornado watch until noon ET. These storms will bring 90 mph straight-line winds, according to weather advisory.

A significant severe storm outbreak from the Great Lakes to the Gulf Coast puts 54 million people at risk. The National Weather Service's Weather Prediction Center forecasts late-season heavy snow and gusty winds across the Great Lakes and Northeast through midweek.

In Wisconsin, a winter storm warning is in effect from 1pm Tuesday to 1pm Wednesday. You may expect wet heavy snow, 40 mph wind gusts, and slippery roads. Snow will continue until Thursday across northeast Wisconsin, with sunny weather expected by Friday.

Central Indiana and Ohio face threats of high winds and hail. The weather service has issued warning of tornadoes in Indiana. An isolated tornado threat exists for the region, according to NBC affiliate WCMH-TV of Columbus, Ohio.

Flooding is a major concern, with 41 million people from Indiana to New Jersey under flood watches. Flash flood warnings have been issued for Pittsburgh and other areas of western Pennsylvania, where 2 to 4 inches of rain has already fallen.

The Great Lakes and Northeast could see a surprise snowstorm with heavy snowfall and strong winds making travel dangerous.

The threat does not stop there. A secondary storm system is expected to bring severe weather to the Mid-Atlantic and Florida, including more rain, wind, and even tornadoes.

Four tornadoes were reported Monday in Oklahoma and Missouri. Damage was reported Tuesday in Lexington and Nicholasville, Kentucky, and Charleston, West Virginia.