Multiple storms tore through Mississippi overnight, killing at least one person and injuring nearly two dozen others, according to state officials quoted by NBC News.

The storm was the latest in a series of extreme weather incidents over the holiday weekend that have left a total of six people dead, injured more than 100 others and cut off power for nearly 500,000 households. As of early Monday afternoon, nearly 468,000 utility customers were still without electricity across a swath of the South, including Alabama, Arkansas, Louisiana, Mississippi, Oklahoma, Tennessee and Texas, according to the online outage tracker PowerOutage.us.

Texas and Louisiana, meanwhile, face a “blistering heatwave,” according to the weather service. At least 12 million people across parts of the Gulf Coast and Southeast face a risk of severe storms capable of producing large hail, damaging winds and isolated tornadoes. Cities facing those threats include Mobile, New Orleans, Savannah and Tallahassee.

Flash flooding may be a concern in some of the same areas, with flood watches in effect for up to 4 million people in parts of Mississippi, Alabama and the western Florida Panhandle.

By midweek, the pelting rain may raise the risk of additional flooding across western Florida, the Mid-Atlantic and parts of the Appalachian Mountains.

Texas, where three people were killed and more than 50 injured on Thursday after a tornado struck the city of Perryton, faced a possibility of record-breaking heat on Monday.

The heat wave is also expected to blanket nearby states: At least 31 million people were under heat alerts on Monday, including parts of Texas, Louisiana and southern Mississippi.

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