Tornadoes and flash flooding expected as 'catastrophic and potentially historic' storm takes aim at central U.S.

A powerful spring storm will bring a barrage of life-threatening weather to a wide corridor of the central U.S. in what the National Weather Service warns is "only the beginning of a multi-day catastrophic and potentially historic event."

The system is expected to produce severe thunderstorms that could trigger multiple strong tornadoes from Texas to Ohio beginning Wednesday, followed by several days of excessive rain that could trigger widespread and historic flooding.

"An entire spring's worth of rain" could fall in just days.

Here's the latest forecast.

Where and when are tornadoes possible?

"A tornado outbreak is expected today and tonight from parts of the lower Mississippi Valley into the Mid-South and lower Ohio Valley," the weather service said in its latest forecast. "Numerous tornadoes, along with multiple long-track EF3+ tornadoes, appear likely."

According to the NWS Storm Prediction Center, a rare 5 out of 5 level risk of severe thunderstorms is in place for parts of the Mississippi Valley, as more than 20 million people from Louisiana to Ohio were in the path of storms that could produce strong tornadoes.

Tornado watches have already been issued for parts of Arkansas, Illinois and Missouri.

'Catastrophic and life-threatening' flooding

Behind the expected tornadoes, a "multi-day, potentially historic heavy rainfall event may produce catastrophic and life-threatening flooding through Saturday from the Ozarks into the Ohio River Valley," the weather service said.

According to the Storm Prediction Center, there is a high risk for excessive rainfall in multiple states, including Kentucky, Missouri, Tennessee and Arkansas, beginning Thursday, with "widespread, life-threatening flash flooding" likely.

The slow-moving front will remain stalled over the central and mid-South through the weekend, dumping potentially historic amounts of rainfall across the region.

Up to 15 inches of rain is possible in some areas, forecasters said.

“Extensive, rare and at times catastrophic flash flooding is likely," forecasters at the NWS office in Little Rock, Ark., said. “Flash flood water levels may reach areas that rarely or have never flooded before.”

The weather service warned communities throughout the region to "prepare now for the possibility of long duration and severe disruptions to daily life given the expected extreme rainfall and flood risk."