Just a little over week ago, parts of middle Tennessee were ravaged by a family of nighttime twisters that struck overnight. Unfortunately, the risk for more severe thunderstorms and tornadoes returns Thursday to the same region.

Throughout the day and into the evening Thursday, the National Weather Service's Storm Prediction Center has placed 17 million people under the risk for severe thunderstorms across portions of the Southeast, Tennessee and Ohio Valleys. Cities included in the risk area include Little Rock, St. Louis, Memphis, Louisville and Nashville.

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There will be two rounds of storms through the day Thursday. The first round will be in the early afternoon and will continue into the evening across portions of Missouri, Kentucky, southern Illinois, Indiana and northern Tennessee. The second round will begin later in the evening and night, and will likely be the more significant. The storms will be capable of bringing damaging winds, large hail and tornadoes – some of which could be strong and after dark. Unfortunately, this means another nocturnal tornado threat for millions.

Nocturnal tornadoes are more than twice as likely to be fatal, given people are sleeping and often do not get the necessary tornado warnings to prompt them to take shelter. Folks in the severe risk area for tonight should make sure they have a way to get warnings whether that means having phones' ringer turned on, keeping the television on or purchasing a NOAA weather radio. Other advice for staying safe during dangerous nighttime storms includes sleeping in the basement or an interior room.

In addition to the severe weather, heavy rainfall could cause isolated instances of flash flooding across parts of northeast Texas, southern Oklahoma, Arkansas, Mississippi, Tennessee and Kentucky. One to two inches of rain, higher amounts locally, could fall across this region through Friday. There could be a secondary area of localized heavy rain across the Ohio River along the Kentucky and Ohio border where up to two inches of rain will be possible.

On Friday, this storm system moves east bringing morning rain to the Northeast, but no flooding or severe weather is expected.

Across the southwest, the National Weather Service has issued flood alerts for 12 million people for parts of southeastern California, southern Nevada and central Arizona, including Phoenix and Las Vegas. On Thursday, heavy downpours will move back into southern California and across Arizona. There is also a risk of strong to severe thunderstorms in this region capable of damaging winds and hail.

On Friday, this storm system kicks into the Rockies and Plains bringing with it rain and some accumulating snow. Through Friday, rainfall totals of one-half to two inches will be possible across the Southwest region, with totals up to three inches especially across central Arizona. Isolated flash flooding, landslides and mudslides are possible.