Potentially deadly flash flooding, high-magnitude tornadoes and baseball-sized hail could hit parts of the midwest and south on Wednesday as severe thunderstorms blowing eastward become supercharged, forecasters warned.

There were tornado warnings Wednesday morning near the Missouri cities of Joplin and Columbia – merely the opening acts of what forecasters expect will be a more intense period of violent weather later on Wednesday, as daytime heating combines with an unstable atmosphere, strong wind shear and abundant moisture streaming into the nation’s midsection from the Gulf.

The potent storm system will bring “significant, life-threatening flash flooding” starting Wednesday and continuing each day through Saturday, the National Weather Service said.

With more than a foot (30cm) of rain possible over the next four days, the prolonged deluge “is an event that happens once in a generation to once in a lifetime”, the service said in one of its flood warnings. “Historic rainfall totals and impacts are possible.”

The flood fears come as residents in parts of Michigan continue to dig out from a weekend ice storm.

Thunderstorms with multiple rounds of heavy rain were forecast in parts of Texas, the lower Mississippi Valley and the Ohio Valley beginning midweek and lasting through Saturday. Forecasters warned the storms could track over the same areas repeatedly and produce heavy rains and dangerous flash floods capable of sweeping cars away.

Rain totaling up to 15ins (38cm) was forecast over the next seven days in north-eastern Arkansas, the south-east corner of Missouri, western Kentucky and southern parts of Illinois and Indiana, the weather service warned.

“We’re potentially looking at about two months of rain in just a handful of days,” Thomas Jones, a weather service meteorologist in Little Rock, Arkansas, said Monday.

Parts of Arkansas, west Tennessee, western Kentucky and southern Indiana were at an especially high risk for flooding, the weather service said.

At least one tornado was spotted Tuesday night in Kansas. “Take cover now!” the weather service’s office in Wichita warned residents on the social platform X. No injuries were reported.

Another tornado touched down in the north-eastern Oklahoma city of Owasso at about 6.40am Wednesday, according to the National Weather Service office in Tulsa. There were no immediate reports of injuries, but the twister heavily damaged the roofs of homes and knocked down power lines, trees, fences and sheds.

Tornado warnings were also issued in Missouri on Wednesday. Authorities in eastern Missouri were trying to determine whether it was a tornado that damaged buildings, overturned vehicles and tore down utility poles, tree limbs and business signs Wednesday morning in and around Nevada, Missouri.

The Missouri state highway patrol reported that the damage shut down a portion of US Route 54 in the city of about 8,300 people about 95 miles (153km/h) south of Kansas City, Missouri.

Along with tornadoes, high winds with gusts of up to 50mph (80 km/h) were also expected across large parts of the midwest.

The ominous forecast comes nearly two years to the day that an EF-3 tornado struck Little Rock, Arkansas. No one was killed, but that twister caused major destruction to neighborhoods and businesses that are still being rebuilt today.

More than 90 million people are at some risk of severe weather in a huge part of the nation that stretches from Texas to Minnesota and Maine, according to the Oklahoma-based Storm Prediction Center.

About 2.5 million people are in a rarely called “high-risk” zone. That area most at risk of catastrophic weather on Wednesday includes parts of west Tennessee including Memphis; north-east Arkansas; the south-east corner of Missouri; and parts of western Kentucky and southern Illinois.

A tornado outbreak was expected Wednesday, and “multiple long-track EF3+ tornadoes, appear likely”, the Storm Prediction Center said. Tornadoes of that magnitude are among the strongest on the Enhanced Fujita scale, used to rate their intensity.

In Michigan, crews worked to restore power after a weekend ice storm toppled trees and power poles. More than 135,000 customers in northern Michigan and 11,000 in northern Wisconsin were still without electricity Wednesday morning, according to PowerOutage.us, which tracks outages nationwide.

Heavy, wet snow also was forecast into Wednesday across the eastern Dakotas and parts of Minnesota.