Forecasters warn of an impending outbreak of long-lasting, strong tornadoes and once-in-a-lifetime flooding

By Karina Tsui, CNN Meteorologist Mary Gilbert

(CNN) — A life-threatening outbreak of long-lived and strong tornadoes is expected today in parts of the central and eastern US from a powerful, wide-reaching spring storm.

Severe thunderstorms were already cutting through the Plains Wednesday morning ahead of the main threat later this afternoon and evening, which carried the highest possible risk level.

Some areas that were hit hard by a deadly storm over the weekend –– and destructive storms in mid-March –– are threatened yet again Wednesday.

As if that weren’t enough, Wednesday will also be the start of a multi-day, once-in-a-lifetime flooding event.

Here’s the latest:

• Severe thunderstorms ongoing: A powerful line of severe storms stretched from Oklahoma to Missouri early Wednesday morning. A few storms prompted tornado warnings and at least three confirmed tornadoes occurred overnight — one in Kansas, near Salina, and two in Oklahoma. Storms will continue to track east into the Mississippi Valley through the morning.

• Tornado outbreak incoming: A tornado outbreak is expected Wednesday in parts of the central and eastern US amid a wide-reaching severe thunderstorm threat, according to the Storm Prediction Center. More than 20 million people from Louisiana to Ohio could be in the path of storms that produce strong tornadoes — rated at least EF2. But that’s not all. “Numerous tornadoes, along with multiple long-track EF3+ tornadoes appear likely,” the SPC warned. The greatest tornado threat will begin later in the afternoon and continue overnight.

• Generational flood event starts tonight: Severe thunderstorms will dump gushing rain on parts of the Mississippi and Ohio valleys starting late Wednesday. It’s the first of many, many rounds of heavy rain to come for the region. More than 15 inches of torrential rain is possible by Saturday — especially in the corridor where Arkansas, Missouri, Illinois, Kentucky and Tennessee meet — and could cause life-threatening, once-in-a-generation flooding. “Extensive, rare, and at times catastrophic, flash flooding is likely… flash flood water levels may reach areas that rarely or have never flooded before,” forecasters at the National Weather Service in Little Rock, Arkansas, said.

Rare high risk for tornadoes today

Tens of millions of people from the Plains to the Mississippi Valley and Midwest could be in the path of intense thunderstorms capable of widespread damaging winds gusts, hail up to the size of baseballs and strong, long-lived tornadoes Wednesday.

Severe thunderstorms in the Plains Wednesday morning will track east into the Mississippi Valley by the afternoon. Some of these storms will strengthen further while others develop Wednesday afternoon and continue into the night.

A rare level 5 of 5 risk of severe thunderstorms is in place for parts of the Mississippi Valley, according to the Storm Prediction Center. Storms in this area could produce multiple long-track tornadoes of EF3 strength or greater.

Strong tornadoes – rated at least EF2 – are also possible from Louisiana to Ohio. The greatest tornado risk will begin in the afternoon and continue into Wednesday night.

By the evening, severe thunderstorms could stretch from Louisiana and Arkansas to as far north as Michigan. A few more storms could develop overnight in Texas.

Many storms will be ongoing after dark, increasing the danger for anyone in their path. Nighttime tornadoes are nearly twice as likely to be deadly as those occurring during the day, a 2022 study found.

The storms will also deliver torrential rain that sets up a new, longer-lasting threat: flooding.

‘Generational’ flooding expected this week

A roadblock in the atmosphere caused by a stalled front will point a firehose of moisture from the Gulf right into the Mississippi and Ohio valleys and create a days-long flooding event this week.

Forecasters predict heavy rain will set up serious and possible historic flooding in Arkansas, Missouri, Tennessee and Mississippi beginning late Wednesday.

A rare level 4 of 4 high risk of flooding rainfall is in place Thursday from extreme northeastern Arkansas through far western Kentucky.

These high-risk flooding events are not to be underestimated as they are issued on fewer than 4% of days per year on average a year but are responsible for more than 80% of all flood-related damage and 36% of all flood-related deaths, Weather Prediction Center research shows.

“This is an increasingly significant setup” with the potential for “high impacts and life-threatening flash flooding spanning the course of several days,” the center warned.

The threat of flooding will ramp up with each passing day starting Wednesday. The ground will get increasingly soaked until it becomes unable to absorb more and any rainfall after that point will set off dangerous flash flooding.

Forecasters predict storms will work over the same areas repeatedly and could drop 2 to 6 inches of rain each day –– especially from Arkansas to Indiana.

By Saturday, areas caught repeatedly under the heaviest storms could end up with more than 15 inches of rain. The corridor where Arkansas, Missouri, Illinois, Kentucky and Tennessee meet are the most likely place for these extreme totals.

“If we get anywhere near these amounts, a historic flash flooding event is likely,” the National Weather Service in Paducah, Kentucky, warned.

An entire spring’s worth of rain could fall in just four days in the hardest-hit locations. Paducah, for example, averages about 14.5 inches of rain from March to May.

The upcoming heavy rain event isn’t the first period of extreme rainfall this season and likely won’t be the last. Overwhelming rainfall is becoming more frequent in a warming world, as rising global temperatures push weather toward the extremes.

Last week, more than half a year’s worth of rain fell in less than 48 hours and sent parts of South Texas underwater, forcing over 100 water rescues and leaving four dead.

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