Storms have unleashed as much as 15 inches of rain across the region, and the forecast offered little hope for relief. Another, larger storm system was brewing along the same path, bringing several more days of rain and the threat of tornadoes.
The greatest flooding threat loomed in the southeastern Missouri community of Poplar Bluff, a town of 17,000 residents about 130 miles south of St. Louis. Six inches of rain fell Monday alone, bringing the four-day total to 15 inches.
By midday, the deluge had caused the Black River to pour over a levee in 30 places. The flood wall, which extends from Poplar Bluff to the town of Qulin downstream, was also breached in at least one place, allowing water to gush through a hole.
"Each heavy downpour, each hour that passes by with the water pushing on that levee, the likelihood of a failure is that much more possible," said Deputy Police Chief Jeff Rolland, calling it was a "miracle" that the first hole did not develop until late morning.
In another area near the confluence of the swollen Mississippi and Ohio rivers, authorities debated a desperate plan to blow up one levee to ease the pressure on others.
Rolland credited emergency crews for their work to bolster weakened areas of the Poplar Bluff barrier and for evacuating residents from about 1,000 homes.
Butler County Sheriff Mark Dodd said the water pouring through the levee was unlikely to make it far enough upstream to add to the threat facing Poplar Bluff, where about 1,000 homes had already been evacuated. But authorities planned to evacuate more homes closer to the breach, which was in a sparsely populated area.
Terry Jones went to St. Louis over the weekend to attend her sister's funeral. By the time she returned to Poplar Bluff, her home was flooded.
"By the time I got out there, water was over my porch," said Jones, a 51-year-old retiree. "My front room is messed up. I don't know about the bedrooms because I couldn't get in."
Jones, who lives with her 12-year-old granddaughter, said she has nowhere to go if her house becomes uninhabitable.
Despite the punishment the region has already endured, the weather was expected to get worse -- and soon. A second system moving through western Oklahoma and North Texas on Tuesday carried the same threat of tornadoes and flooding but over a broader area that stretched from Dallas to northern Louisiana and up to Memphis.
Greg Corbin, the warning coordination meteorologist for the National Weather Service's Storm Prediction Center in Norman, Okla., said having two such storms in such rapid succession is unusual.
"It's basically in the same place for two days in a row. That doesn't happen very often. Such rapid succession doesn't give any time for a break," Corbin said.
In 2008, flooding damaged or destroyed hundreds of homes in Poplar Bluff, raising doubts about whether the levee was capable of protecting the town during heavy rain. A federal inspection gave the levee a failing grade, and the private district that maintains the levee has been unable to make repairs.
The storm system dumped rain on several states over the past week, soaking Arkansas, Illinois, Indiana, Kentucky, Missouri, Mississippi and Tennessee.
The storms spawned at least one tornado Monday in Arkansas that killed four people and blasted a path of destruction through the town of Vilonia, 25 miles north of Little Rock. Four other people were killed in floods.
On Tuesday, the National Weather Service sent survey teams to Vilonia and nearby Garland County to investigate the damage and assess how much of it was caused by tornados or straight-line winds.
"It wouldn't surprise me if we were to end up with a count of 10 or 12 tornadoes by the time all the surveys are completed," said John Robinson, another weather service meteorologist.
Authorities in Mississippi say a 3-year-old girl in the city of McComb was killed when a storm toppled a large tree onto her family's home. The girl's parents, who were in the room with her, were both injured.
Governors in Arkansas and Kentucky declared states of emergency. In the sleepy town of Smithland, Ky., residents fled their homes Tuesday while hundreds of volunteers piled sandbags along the riverfront. The water was rising 6 inches a day.
Back in Poplar Bluff, authorities watched the levee closely. If it were to fail entirely, the rushing floodwaters could destroy or severely damage 500 homes in Poplar Bluff and its outskirts and potentially displace some 7,000 people in the surrounding flood plain. Already, 23 small businesses have taken on water, Rolland said.
The Army Corps of Engineers postponed until Wednesday its decision on a proposal to intentionally breach the Birds Point levee in southeast Missouri, just downriver of the confluence, in a desperate bid to reduce the amount of water moving down the Mississippi.
Gov. Jay Nixon opposed the plan, which would soak 130,000 acres of farmland. And the state attorney general filed a lawsuit Tuesday in federal court seeking to block the engineers' proposal.
Families forced to flee their homes Monday watched as murky floodwaters crept into their yards. Sandbagging wasn't an option because the river simply rose too quickly.
"By the time we realized what was happening, it was too dangerous to sandbag," Butler County Presiding Commissioner Ed Strenfel said.
Hotels filled up, and 300 people took shelter at the Black River Coliseum, the town's 500-seat concert venue. The Missouri National Guard sent 200 guardsmen and rescue equipment to the area. Several people had to be rescued by boat.
Poplar Bluff Police Chief Danny Whiteley was hoping the water would recede soon enough that flooding would mostly be limited to basements. He wasn't optimistic.
"I guess you'd call it a perfect storm: It's just all come together at once," Whiteley said.