Millions in the United States are under alert for severe storms and a possible heat record

() — More than 50 million people across the southeastern United States face the threat of severe storms Monday as widespread power outages have left nearly half a million people across the South in the dark, including some under sweltering record temperatures.

There is a slight level 2 of 5 risk of severe weather in parts of the Gulf Coast and Southeast, including the cities of New Orleans and Baton Rouge in Louisiana; Jacksonville, Florida; Mobile, Alabama; and Savannah, Ga. The main threats are damaging wind gusts, large hail, and isolated tornadoes.

A level 1 of 5 marginal risk stretches from central Texas to southern Florida and north to western North Carolina, leaving cities like Atlanta, Charlotte, North Carolina; Austin, Texas; and Tampa, Orlando and Miami in Florida under the threat of large hail and damaging wind gusts.

The same system sparked a tornado in Mississippi late Sunday, causing multiple injuries and structural damage in Bay Springs and Louin, according to preliminary reports from the National Weather Service.

The Jasper County Sheriff’s Department reported in a publication of Facebook that a shelter will open this Monday morning “for all those displaced by the recent destruction caused by the tornadoes.”

Meanwhile, about 35 million people are under alerts for a scorching heat wave that has settled across much of Texas, Louisiana and southern New Mexico and Mississippi, according to the National Weather Service.

Many braved the heat without air conditioning, as nearly 500,000 customers were without power in the South as of Monday morning, including more than 200,000 in Oklahoma and more than 90,000 in Texas and another 85,000 in Louisiana, according to PowerOutage.us.

The National Weather Service advises residents to stay indoors during the hottest part of the day, drink plenty of water, and not leave children or pets in vehicles.

“In case we haven’t said it enough”, tweeted the Midland, Texas National Weather Service is going to be “HOT. Try to spend as little time outdoors as possible, but if you must be outside, take frequent breaks in the air conditioning, drink plenty of water, and spend as much time as possible in the shadow”.

As the heat wave continues, more than 40 daily records across Texas could be broken or equaled this week. The worst of the heat is expected Monday through Wednesday.

The combination of temperature and humidity — or the heat index — could climb to 45 and 50 degrees Celsius in cities like Houston, San Antonio, Brownsville and Dallas.

This Sunday several daily heat records have already been broken. Del Rio, Texas, registered a temperature of 44 degrees this Sunday, breaking a previous daily record of 42 degrees set in 2011. Austin Camp Mabry, Texas, tied its record of 41 degrees set a dozen years ago and McAllen, Texas, reported a record 40 degrees.

“Temperatures in the 40s will not only rival daily high temperature records for the nation, but could tie or break existing records,” the National Weather Service said. “There will be little relief overnight with lows in the upper 21 and 26.”

Cities across the South — some still cleaning up from last week’s storms — are preparing for hot weather by opening cooling centers.

The city of Houston will have refrigeration centers open again from 3:00 p.m. to 7:00 p.m. this Monday as the city prepares for high temperatures. Caddo Parish, in Louisiana, has opened more cooling centers as the parish continues to deal with power outages and storm cleanup.

The New Orleans Emergency Preparedness Campaign is working with the New Orleans Fire Department to set up hydration stations that provide water and sun protection this Sunday and Monday.

Meanwhile, there were more than 70 storm reports across the Southeast on Sunday, including six reports of tornadoes, the majority in central Mississippi, according to the Storm Prediction Center.

Hail 2 inches wide or larger was also reported Sunday in Hunt, Texas, and Kerrville, Texas.

On Monday, the threat of excessive rainfall moves east into the southeast of the country, bringing the threat of thunderstorms and flooding over parts of the Southeast, the southern Mid-Atlantic and the southern Appalachian Mountains.

‘s Jamiel Lynch, Mitchell McCluskey and Devon Sayers contributed to this report.