Other cities potentially in harm's way but at lower risk for tornadoes included Chicago, Nashville, Tennessee, St. Louis, Missouri, Madison, Wisconsin and Des Moines, Iowa.
"There's a potential for some very strong tornadoes and some tornadoes that could be on the ground for quite some time, especially in northern Arkansas and western Tennessee," said John Feerick, senior meteorologist at private forecasting service AccuWeather.
Feerick said the storm system would intensify through Friday as the sprawling low-pressure system at its core moves farther eastward, drawing up greater moisture from the Gulf of Mexico.
Dust storm warnings were in effect for portions of the Southern Plains.
Reporting by Steve Gorman in Los Angeles; Editing by Jamie FreedOur Standards: The Thomson Reuters Trust Principles.