By Hanna Park and Mary Gilbert, CNN Meteorologist

(CNN) — Millions of people are under tornado watches across the central United States on Sunday – and confirmed tornadoes have been reported in Michigan and Missouri – as a volatile weather system has triggered power outages and huge hail.

Roughly 170 million people from Illinois to eastern Texas and beyond could be affected over the next two days, as a powerful cold front collides with unseasonably warm air.

March has already delivered an extraordinary number of tornado reports, surpassing the number from the same time last year. Some of the same regions struck by deadly storms earlier this month could once again find themselves in harm’s way.

Sunday’s threat: golf ball-sized hail and long-lived tornadoes

Weekend temperatures from the Plains to the East Coast have felt more like late May or early June, but Sunday’s cold front brought an abrupt end to the unseasonable warmth, triggering thunderstorms as the cooler air collided with the warm, moisture-laden air ahead of it.

Photos sent to CNN affiliate KOCO late Saturday showed hailstones ranging from about the size of a quarter to a golf ball, many of them spiked.

In the wake of winter storms, more than half a million customers were without power in Michigan and 65,182 without power in Wisconsin, as of Sunday evening, according to poweroutage.us. Some areas of Wisconsin saw a tenth of an inch of ice or more Sunday. There were also more than 100,000 customers without power in Indiana.

A total of 12 million people are under tornado watches, spanning from Indiana to Arkansas, as of Sunday evening.

A tornado watch is in effect for portions of northern Arkansas, southern Illinois, southwest Indiana, western Kentucky, southeast Missouri and western Tennessee until 11 p.m. CT, according to the Storm Prediction Center. The watch area includes Jonesboro, Arkansas; Paducah, Kentucky; and Memphis, Tennessee.

A tornado watch was issued before 7 p.m. ET, scheduled to last until 1 a.m. ET for northern Kentucky and southwest Ohio.

Intense thunderstorms are expected to strike after nightfall, heightening concerns. Tornadoes that occur at night are nearly twice as likely to be fatal as those during daylight hours, a 2022 study found.

Some storms are expected to bring heavy rainfall, raising the risk of flash flooding across regions from the South to the Midwest.

Storms will span most of the East Coast Monday

The severe weather threat will spill into Monday as powerful thunderstorms continue to sweep eastward from the Appalachians to Louisiana and Mississippi during the morning hours. While some storms may briefly weaken with the morning light, they are expected to regain strength by the afternoon.

By Monday evening, the severe weather threat will span nearly the entire East Coast, placing nearly 100 million people at risk. Cities from New Orleans to Boston fall within the affected zone, though the specific threats will vary.

The Northeast’s primary threat will be damaging wind gusts. A huge swath of the South, from the mid-Atlantic to the Gulf Coast, will face the full spectrum of severe weather hazards, including hail, tornadoes and strong winds.

The storms are expected to linger overnight from the mid-Atlantic to the Northeast before moving into the Atlantic Ocean by Tuesday morning.

A historic March for tornado activity

This year has already seen an extraordinary number of tornadoes, with approximately 300 tornado reports logged since January, nearly double the 164 reported by this time last year. Since 2010, only three years — 2023, 2017 and 2013 —have recorded more tornadoes in the first three months of the year.

Last year tornado activity surged in late spring and persisted through December, resulting in nearly 2,000 tornado reports. It was the second-most tornado reports in a single year on record, surpassed only by 2017.

This spring’s procession of severe storm systems looks likely to continue. With this week’s threat looming, forecasters are already monitoring a large area from Texas to the Midwest for another potential round of thunderstorms on Wednesday.

Residents across all affected regions are urged to stay informed and have multiple ways to receive weather alerts, especially in areas at risk for nighttime storms.

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