Forecasters are upgrading the likelihood that severe storms and strong tornadoes could strike parts of the South less than a week after a twister killed 23 people in Alabama.

A region that includes parts of Arkansas, Mississippi, Louisiana, Tennessee, Kentucky, Illinois, and Missouri will be at heightened risk of severe weather Saturday, the national Storm Prediction Center reported Friday. The area is home to 2.6 million people, and includes the Memphis, Tennessee metropolitan area.

A broader area that includes more than 10 million people — stretching from east Texas to Alabama, Tennessee and Kentucky — is at a slightly lower risk of severe storms and tornadoes.

The storms will be fast-moving, racing to the northeast at 50 to 60 mph (80 to 97 kph), said Bill Bunting, chief of forecast operations at the Storm Prediction Center in Norman, Oklahoma.

"It means you have to take action when warnings are issued and not wait until you see the threat visually," he said. "If you wait until you see an approaching tornado with damaging winds, it's going to be at your location within seconds."

As the sun rises Saturday, storms and possibly tornadoes will likely be moving through east Texas and parts of Louisiana and Arkansas, the National Weather Service is projecting.

Saturday night, the threat will likely continue after dark as the storms move east into Alabama, forecasters said. That poses a particular danger as many people are often asleep.

"It can be more difficult to reach people at night," Bunting said. "Just make sure you know how to the get the warnings if it's in the middle of the night."

Forecasters across the region were studying computer models and tracking the system's progress. Some characteristics, such as strong wind shear, have them concerned.

"It's sort of like making a cake — if the ingredients can all really come together we could certainly have multiple tornadoes across the broad region," said Andrew Pritchett, a meteorologist at the National Weather Service in Huntsville, Alabama.

Rain could help cool the atmosphere and block the heat that fuels severe storms. But that could also exacerbate flooding in the region, where rivers are already running very high, Prichett said. Up to two inches (5 centimeters) of rain is expected in northern Alabama.

"So it's a very delicate balance — we don't need the rain, but we're hoping that maybe the atmosphere will stay more rain-cooled throughout the day and help mitigate the severe weather threat," he said.

President Donald Trump planned a Friday visit to Lee County, Alabama, where a tornado outbreak across the Southeast last Sunday wreaked its worst havoc, killing 23 people. It was the deadliest to hit the U.S. since May 2013, when an EF5 twister killed 24 people in the Oklahoma City suburb of Moore.

The National Weather Service has confirmed at least 38 tornadoes touched down in Alabama, Georgia, Florida, and South Carolina as punishing storms crossed the region Sunday.

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Martin reported from Atlanta. Associated Press Writer Russ Bynum in Savannah, Georgia, contributed.