ST. LOUIS -- Rivers in the nation's heartland are rising again, and with heavy rain in the forecast, parts of Iowa, Missouri and Illinois are bracing for yet another round of flooding.

The National Weather Service said Wednesday that 2 to 4 inches of rain will be common as strong storms fire up through Friday. Pockets of the region could see up to 6 inches of rain, said weather service hydrologist Mark Fuchs, meaning a second round of spring flooding in many river towns.

"We're probably going to see some major flooding when all is said and done," Fuchs said. Though buyouts during the last two decades have removed most homes from the flood plain, the flooding would swamp thousands of acres of farmland and close dozens of roads.

How major will depend on how much rain falls -- and where. A worst-case scenario would be widespread heavy rain along the Mississippi River north of St. Louis and along the Missouri River. The Mississippi and many of its tributaries already are above flood stage, and the Missouri is getting close.

The Mississippi River was at 29.86 feet at Cape Girardeau on Wednesday afternoon. Flood stage is 32 feet.

Projections had the river reaching 39 feet by Wednesday morning.

The expected downpours will add to what has been an extremely wet spring -- the wettest on record in Iowa, where the Iowa, Skunk and Chariton rivers are topping their banks, along with the Mississippi. Further south in several towns north of St. Louis on either side of the Mississippi, the river is a few feet above flood stage.

St. Louis, sitting near the confluence of the nation's two largest rivers, could see its worst flooding since the river peaked nearly 12 feet above flood stage in 1995, Fuchs said. A lengthy flood wall protects industrial areas near downtown, but flooding could cause drainage concerns and close some St. Louis streets. The flood also would possibly shut down a handful of riverfront businesses, such as cruising boats and bike rentals near the Gateway Arch. The Arch itself sits high enough from the river to be out of harm's way.

Gary Christmann, emergency management commissioner for St. Louis, said sandbags are ready if needed, but no homes are expected to be in danger.

Small towns and rural areas are casting a wary eye, too.

Mike Peterson of the U.S. Army Corps of Engineers said nine levees were overtopped during the April spring flooding and have yet to be repaired. They included levees on the Illinois and Kaskaskia rivers in Illinois and seven on the Mississippi -- all in Pike and Lincoln counties in northeast Missouri.

Petersen said most of the damaged levees protect agricultural land.

"We've got plenty of sandbags and pumps, so we're prepared should floodwaters come up," Petersen said.

Clarksville, Mo., left up a makeshift levee of sandbags, boards and plastic from the earlier flood. Good thing: The forecast calls for the Mississippi to rise about 9 feet above the 25-foot flood stage by Saturday, again threatening the small downtown's shops and restaurants.

"This is one of those instances where the flood came, it went away, and some people began to relax a little," Mayor Jo Anne Smiley said. "We believed we needed to be diligent in keeping the wall intact."

Volunteers spent Wednesday reinforcing the sandbag levee, but Smiley said no one will know until floodwaters arrive how well it will hold.

In Iowa, an average of 16.4 inches of rain has fallen statewide since March, nearly an inch more than the previous record for the three-month period set in 1892, with more on the way. Across the state, emergency management officials were reviewing flood preparation plans and protecting the most vulnerable areas, including the state's two biggest universities.

At the University of Iowa in Iowa City, temporary aluminum flood walls anchored in concrete are being placed around a dorm damaged in 2008 flooding. The 84 people living there for the summer semester have been moved.

Iowa State University in Ames closed an athletic center for sandbagging because of flood concerns, and flood gates were installed at numerous other buildings.

Heavy rain earlier this week caused flash flooding that's blamed in the death of a 71-year-old Iowa man, whose sport utility vehicle had been submerged in a northern Iowa creek since Monday morning.

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AP reporter David Pitt in Des Moines, Iowa, contributed to this report.