Severe storms could bring tornadoes and golf-ball-sized hail to parts ...

More than 8 million people are at risk of being lashed by powerful tornadoes Tuesday as an intensifying round of severe thunderstorms – which also carries the threat of severe winds and hail larger than golf balls in some areas – rumbles from the Southeast to the Ohio Valley.

The sprawling storm system has brought the greatest risk of severe thunderstorms so far this year. Severe thunderstorms pummeled parts of Texas all the way to Illinois on Monday, bringing reports of three tornadoes in Oklahoma and pelting some places with hailstones larger than baseballs.

More than 75 million people are under severe storm threat from eastern Louisiana to southwestern New York on Tuesday.

The greatest risk for intense, potentially long-track tornadoes – ones that tear through several miles of land – extends from southeast Indiana across Ohio and over portions of Kentucky and West Virginia, the Storm Prediction Center forecasts.

Some hailstones could exceed 2 inches in diameter and destructive winds could reach up to 75 mph, the prediction center said.

Over 17 million people are under flood threat from Illinois to Maryland on Tuesday morning, with flood watches lasting into the evening and rainfall totals of up to 5 inches possible.

Storms are likely to reach their peak strength Tuesday afternoon and evening – but could persist overnight in some areas.

The prediction center has urged residents in the storms’ path to monitor forecasts because the areas under risk could change. “Now is the time to ensure you have a severe weather action plan in place,” it advised.

Tuesday’s risk for severe storms was upgraded to a Level 4 of 5 for parts of Ohio and parts of Indiana, Kentucky and West Virginia.

Much of Ohio is at risk of seeing strong tornadoes Tuesday. The state, which typically averages 22 tornadoes per year, is second only to Florida for the number of preliminary reports of tornadoes so far this year, according to data from NOAA. At least 26 tornadoes have been reported across parts of Ohio while 30 have been recorded in Florida.

Part of the Southeast extending from Alabama to southern Pennsylvania, is under an enhanced risk, or Level 3 of 5, for severe storms, including potential tornadoes and large hail, according to the National Weather Center. The area includes the cities of Nashville, Birmingham, Knoxville and Huntsville.

The same severe weather system tore through the central US on Monday, prompting more than 100 storm reports across the region. Massive hailstones were reported in Texas, including one as large as 4.5 inches in Briar – bigger than a softball.

The storms will continue to wreak havoc on Wednesday as cold air pushing into the northern edge of the system begins to form a wintry mix of rain and snow.

Wednesday’s wintry mix

Rain will transition to snow and a wintry mix later Tuesday in areas of the Midwest and Great Lakes, and rain and snow showers will continue in parts of both regions through Thursday.

Cities including Chicago could even see a few flakes, but little accumulation of snowfall is expected.

The highest snowfall totals are expected across the parts of Michigan andWisconsin, where snowfall of 6 to 12 inches is possible through Wednesday afternoon. Some parts of Michigan may receive over a foot of snow forecast to last into Thursday, possibly snarling morning and afternoon commutes.

Winter-like weather will shift into the interior Northeast beginningWednesday,where winter storm watches are in effect for much of the interior region through Friday.

The Adirondacks could see up to a foot of snowfall by Thursday, while parts of the Green and White Mountains can see over a foot of snowfall. Gusts up to 50 mph combined with heavy snowfall can cause blowing snow and can cause power outages and travel delays.

Major cities across the Northeast, including New York City, Boston and Philadelphia, are currently forecast to see rain.

CNN’s Mary Gilbert contributed to this report.