May Rainfall Smashed Monthly Records, Leading to Record River Flooding in Parts of Kansas, Oklahoma, Arkansas

So far, nine locations have set new record river levels during this prolonged siege of heavy rain.

Hardest hit, so far, is the Arkansas River, where record levels have already been set near Ponca City, Oklahoma, Van Buren/Fort Smith, Dardanelle, Morrilton and Toad Suck Reservoir, Arkansas. The record at Morrilton, Arkansas, had stood since the Great Flood of 1927.

For the first time, the U.S. Army Corps fully opened all gates at the Ozark Lock and Dam near the town of Ozark, Arkansas, Tuesday, essentially allowing the swollen river to move freely through the structure.

The river also reached its highest level since the 1986 flood in Tulsa, Oklahoma, putting unprecedented stress on the levee system, and crested at its highest level since 1943 in Muskogee, Oklahoma, due to heavy rain upstream in northern Oklahoma and southern Kansas.

(LATEST NEWS: Preparations Ahead of 'Worst Flood in Our History')

Given this forecast, water could also overtop levees in Conway and Faulkner Counties, including the Lollie Levee, affecting areas in the city of Conway, Arkansas, about 25 miles northwest of Little Rock. At least one levee has already been overtopped in Perry County.

Next week, the highest crests since 1945 in Little Rock and 1957 in Pine Bluff, Arkansas, are possible, though record flooding isn't expected in either location, according to the National Weather Service.

Floodwater had already overtaken Island Harbor Estates and Regional Park in Pine Bluff on Memorial Day.

Over 300 river gauges in the United States are reporting levels above flood stage, primarily in the nation's midsection.

(MORE: Latest NWS River Forecasts)

Last week, another record river crest was set along Bird Creek in Avant, Oklahoma, about 25 miles north of Tulsa. Fancy Creek at Randolph, Kansas, and the Chariton River near Prairie Hill, Missouri, also set a new record river level.

Record or near-record flooding is possible along stretches of the Grand and Chariton Rivers in northern Missouri, the Illinois River downstream from Havana, Illinois, and the Big Blue River at Blue Rapids, Kansas.

The Missouri River is at its highest level since 1995 in Jefferson City, Missouri, where an EF3 tornado tore through last week.

Next week, St. Louis will see its second major crest of the Mississippi River in just under a month, a crest topped only by the Great Flood of 1993, possibly a couple feet higher than the Mississippi River flood of 1973.

A crest about 2 feet lower than the 1993 record may occur upstream in Hannibal, Missouri. Davenport, Iowa, will see an early June crest about 1 foot lower than the May 2 record crest, leading to flooding in some areas. Burlington, Iowa, is expected to see a top three crest, behind only 2008 and 1993.

(MORE: Why the Midwest, Plains Have Been Most Extreme Weather Regions in 2019)

That volume of water from the upper Mississippi and Arkansas River Valleys will then drain downstream, reaching the lower Mississippi Valley in early to mid June.

If these forecasts hold, the U.S. Army Corps of Engineers will gradually open the Morganza Spillway upriver from Baton Rouge, Louisiana, on June 6 for only the third time in its history, previously done only in 1973 and 2011.

Constructed in 1954, this structure would divert some water from the Mississippi River into Louisiana's Atchafalaya Basin to minimize stress on Mississippi River levees downstream and avoid overtopping.

"The current flood fight is historic and unprecedented," said a U.S. Army Corps statement issued on Monday.

Monday was the 214th day of the flood fight and "is expected to surpass the 1973 event (225 days) as the longest flood fight," the statement said.

(MORE: Longest-Lasting Mississippi River Flood Since 1927)

How Much More Rain?

There is both good and bad news for the flood zone.

The bullish, stubborn jet-stream pattern responsible for this severe weather and heavy rain saga has shifted.

(MORE: Pattern Change to End Severe Siege)

However, scattered thunderstorms, including some overnight thunderstorm clusters will return to the Plains this weekend, and may be a daily and nightly occurrence through much of next week.

These daily storms starting this weekend probably won't bring anything near the magnitude of the widespread, record-smashing rain we've seen in May.

But these thunderstorm clusters could at least bring more localized flash flooding and compound the ongoing long-term river flooding issues.

NOAA's Climate Prediction Center highlighted parts of the Plains and Southeast with higher chances of above-average precipitation in their 6- to 10-day precipitation outlook.

NOAA's Weather Prediction Center also circled part of this region with a threat for heavy rain in the first week of June.

Monthly Rain Records

Rainfall amounts have been staggering over parts of the Plains.

A number of locations from Oklahoma and southern Kansas to western Missouri picked up over a foot of rain in May.

(MORE: The Wettest 12 Months in U.S. History)

Kansas City set a new May rainfall record Tuesday, topping the previous record from 1995, and ranking it among its wettest months all-time.

Over 15 inches of rain soaked Bartlesville, Oklahoma, tripling its average May rain, crushing its previous May record of a mere 10.31 inches in 2000 and less than 1 inch away from the city's single wettest month record of 16 inches in June 1957.

All-time May monthly rain records were just out of reach in Chanute, Kansas (18.35 inches in May 1990), Wichita, Kansas (13.14 inches in 2008), and Enid, Oklahoma (15.85 inches in May 1982), despite each city picking up over a foot of rain.

Chanute, Kansas, picked up more rain in May - 18.01 inches - than it averages from May through July, combined (16.20 inches).

According to an analysis by the National Weather Service's Arkansas-Red Basin River Forecast Center, parts of southern Kansas have picked up over 60 percent of their average yearly precipitation in May alone.

Also setting May rainfall records were Chicago, for the second May in a row, and Paducah, Kentucky.