Severe storm threat eyes millions across Southeast, Deep South from powerful cross-country storm

Back-to-back cross-country storms are expected to bring heavy rain to millions east of the Mississippi River, the first of which begins Thursday, bringing a severe weather threat to parts of the central U.S. and Deep South, while the potential for flash flooding develops across the Tennessee Valley on Friday.

WINTER WEATHER ALERTS STRETCH OVER 600 MILES AS BACK-TO-BACK STORMS UNLEASH SNOW, ICE THREAT

The first storm is expected to develop in the Southwest on Wednesday and bring a blanket of steady rain over Phoenix and Tucson, Arizona, and into Albuquerque, New Mexico.

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Ahead of the storm, a cold front will bring a low-level severe thunderstorm threat to the Southern Plains, including Oklahoma and North Texas beginning Wednesday afternoon, with damaging wind gusts and hail being the primary threats.

This first cross-country storm will then race out of the Southern Rockies in earnest on Thursday and is expected to bring rain across much of the Southern Plains, with some of the heaviest downpours across parts of Oklahoma, Missouri and Kansas on Thursday morning. 

The system will sprint through the Midwest through the day and a widespread area of rain will cover Chicagoland in Illinois, Wisconsin and Indiana and reach into parts of the Ohio Valley into the evening.

Meanwhile, several rounds of thunderstorms will be possible across the Mississippi River Valley Thursday.

A cold front associated with the first storm will move into the Deep South on Friday, sparking the potential for the most significant severe weather threat this week.

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NOAA's Storm Prediction Center has issued a Level 2 out of 5 risk of severe thunderstorms for an area covering more than 8 million people across the Lower Mississippi and Tennessee valleys, including parts of Missouri, west Tennessee, Arkansas, Mississippi, Alabama and Louisiana.

This covers Memphis, Tennessee, Jackson, Mississippi and Alexandria, Louisiana. These storms could be capable of generating damaging wind gusts, hail and possibly tornadoes.

On Friday, the second storm will develop once again in the Four Corners and move out of the southern Rockies, bringing another round of rain to many of the same places as the first storm in the Midwest, and in the Mississippi and Tennessee valleys.

RECORD HIGHS POSSIBLE AS MILLIONS EXPERIENCE SURGE IN WINTER WARMTH ACROSS SOUTHERN PLAINS TO MID-ATLANTIC

NOAA's Weather Prediction Center has issued a Level 2 out of 4 threat of flash flooding for Middle Tennessee and northwestern Alabama through Saturday, where more than 2-3 inches of rain are possible.

The Nashville, Tennessee metro area is currently just outside of this Level 2 threat. 

Rain from the first storm will arrive in the Northeast and New England, including Washington, D.C., Philadelphia, New York City and Boston sometime Friday morning.

Rain is expected to linger across the Southeast Saturday morning as the second storm shifts into the Great Lakes region by the afternoon. 

Showers and thunderstorms are expected across much of the Northeast and New England coasts through Saturday.

Conditions are expected to improve by late Sunday, with most areas drying out by Monday.