LITTLE ROCK, Ark. – Parts of the South and Midwest, still reeling from violent storms, tornadoes and flooding that have killed more than a dozen people, face new flooding and tornado warnings that forecasters said could last for days.

Severe thunderstorms have swept through a swath of the country with a population of 2.3 million people from northeast Texas through Arkansas and into southeast Missouri.

What has happened?

In Kentucky, more than 500 roads were closed by Sunday because of the floods and mudslides. Two people were killed, including a 9-year-old boy who was swept away as he walked to a school bus stop.

The downtown area of Hopkinsville, Kentucky — a city of 31,000 residents 72 miles (116 kilometers) northwest of Nashville, Tennessee — was submerged.

The first wave of storms killed at least five people in Tennessee and one each in Missouri and Indiana on Wednesday and Thursday.

Tennessee Gov. Bill Lee called the devastation in his state “enormous” and said it was too early to know whether there were more deaths as searches continued.

There was massive destruction in Lake City in eastern Arkansas, where homes were flattened and cars were flipped and tossed into trees.

More than 300 tornado warnings were issued by the National Weather Service since the tornado outbreak began early Wednesday, and new warnings followed overnight in Alabama and Mississippi, along with flash flood warnings in Kentucky, Mississippi and Tennessee. The number of tornado warnings eclipsed those issued during last month’s deadly outbreak in Arkansas, Mississippi, Missouri and other states.

Not all tornado warnings involve an actual tornado, and it was too early to know how many were actually produced by the current outbreak.

The severe weather also caused travel headaches.

Hundreds of flights have been canceled and more than 6,400 flights delayed, according to FlightAware.com, which reported 74 cancellations and 478 delays of U.S. flights early Sunday. The flooding also led to road closures in Kentucky and southern Illinois, among other places.

The severe weather hit at a time when nearly half the National Weather Service’s forecast offices have 20% vacancy rates — twice that of a decade ago — according to data obtained by The Associated Press.

What’s causing this wave of storms?

Forecasters attributed the violent weather to warm temperatures, an unstable atmosphere, strong wind shear and abundant moisture streaming from the Gulf.

The prolonged deluge, which could dump more than a foot (30 centimeters) of rain over a four-day period, “is an event that happens once in a generation to once in a lifetime,” the National Weather Service said.

What’s next?

Private forecasting company AccuWeather said northeastern Arkansas, southeastern Missouri, southern Illinois, western Kentucky and northwestern Tennessee needed to prepare for a catastrophic risk from flash flooding.

“This is a rare and dangerous atmospheric setup,” said Jonathan Porter, AccuWeather chief meteorologist.

Forecasters have also warned of major disruptions to shipping and supply chains. Shipping giant FedEx, for example, has a massive facility in the danger area, in Memphis Tennessee. Barge transportation on the lower Mississippi River could also be affected.

Water rescue teams and sandbags were being set up across the region in anticipation of flooding, and authorities warned people to take the threat of rising water seriously and to not drive through water.

Kentucky Gov. Andy Beshear said flooding had reached record levels in many communities.

“Kentuckians and communities have been affected across the state, and teams are working around the clock to support them,” he said Sunday on social media platform X.

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Associated Press writers George Walker IV in Selmer, Tennessee; John Seewer in Toledo, Ohio; Jeff Martin in Atlanta; Adrian Sainz in Memphis, Tennessee; Jonathan Mattise in Nashville, Tennessee, Seth Borenstein in Washington; Bruce Schreiner in Shelbyville, Kentucky; and Sophia Tareen in Chicago, contributed.