August 2023 mid-south U.S. floods

In the early morning hours of August 2, convection developed across northern Missouri in an increased low-level convergence zone, precipitable water values around 2 inches, and a moist, moderately unstable airmass with most-unstable convective available potential energy (CAPE) around 2000 j/kg.[1] The strengthening low-level convergence zone paralleled a west-northwesterly flow aloft, allowing training convection to occur.[1] The convection then merged into a mesoscale convective system several hours later with the convection spreading from southwestern Iowa to southeastern Missouri with abundant moisture and convective instability, along with a strong low-level convergence zone, sustaining the convection, causing heavy rainfall across portions of eastern Missouri and southern Iowa.[2] Shortly thereafter, the mesoscale convective system then expanded into eastern Nebraska, caused by a low level jet, as additional convection developed with a thermodynamic advection occurring.[3] The low level jet then moved to the east and weakened, which caused the convection to dissipate.[3]

Thereafter, on the evening hours, a frontal boundary over central Kansas, along with a humid and moist airmass and instability in southern Missouri, allowed convection to develop and produce heavy rainfall across central Missouri, and west of the Greater St. Louis area as a high risk of excessive rainfall was issued.[4] Training showers and thunderstorms developed across portions of southeastern Missouri and southern Illinois along an elevated convergence axis zone as it moved southeastward towards southwestern Indiana and western Kentucky.[5]

On August 3, mesoscale convective vortex was present along the training convection which caused flash flooding across southeastern Missouri, southern Illinois, western Kentucky, and northwestern Tennessee as the mesovortex moved southeastward.[6] Areas along a isentropic lift above a surface front received heavy rainfall across western Kentucky, southern Illinois, and southeastern Missouri, and high precipitable water values between 2-2.4 inches and convective instability between 1000-2000 j/kg also supported heavy rainfall.[7] Late in the morning, a second mesoscale convective system moved through areas that had already received flash flooding, causing additional heavy rainfall as the MCS weakened and moved southeastward. Additional factors, including a convergence boundary, precipitable water values around 1.8 inches, and moisture/convective instability all contributed to rainfall rates around 2 inches (51 mm) per hour and causing flash flooding.[8]

In the early morning hours of August 4, additional showers and thunderstorms developed in a corridor extending from central Missouri to northern Alabama due to an increased convective instability, a surface stationary front located over Memphis, Tennessee, and a deep-layer mean flow which resulted in repeating rounds of thunderstorms that moved southeastward over the same areas which had already received heavy rainfall.[9] The convective activity led to flash flooding across Union City, Tennessee, and soon moved into portions of northern Alabama, causing flooding across roadways in the state and in Oneonta, Alabama.[9][10]

Water rescues and evacuations occurred at a mobile home park in Union City, Tennessee, where more than two dozen people were rescued, including by boat.[11][12][13][14] Union City was also flooded.[15] Search-and-rescue operations were conducted in Obion County, Tennessee.[12] Businesses, including a Lowe's store, were flooded in southwest portions of Union City.[16] Flooding forced Obion County Schools to cancel classes on August 4.[17] The National Weather Service in Memphis, Tennessee called the flooding in Union City and surrounding areas "catastrophic".[12] A portion of Interstate 40 was closed.[12] 11.49 inches (292 mm) of rain fell in Union City, which prompted a flash flood emergency.[13][18] Firefighters in Rives pumped out floodwaters, and utilized drones to display the flooding situation.[19] Roads in Dyer, Jackson, and Trenton were flooded, and Jackson, Madison, and Gibson counties in Tennessee had roads were flooded as well.[20][21] Flooding also occurred in Weakley, Crockett, and Greene counties in Tennessee.[22] Memphis was also under a flood advisory.[23]

Flash flood emergencies were issued for Union City, and Hickman, Kentucky.[24][25][26] Mudslides also occurred in downtown Hickman, sliding onto roads, which led to closures, including a closure on Kentucky Route 94, a road which led to downtown Hickman.[17][27] Several evacuations occurred in Fulton County, Kentucky.[28]

Portions of Missouri received heavy rainfall, including Columbia, Missouri, receiving 3.77 inches (96 mm) on August 3, breaking a 113-year record.[24][29] Portions of Sikeston and Chaffee flooded, with the latter location including nearby a high school.[30] Roads were flooded across numerous counties in Missouri.[31][32][33] The Missouri River 340 ended as a result of heavy rain, which caused the river's water level to rise, posing a hazard.[34] Hundreds of power outages occurred across the state.[32] Water rescues and flooded roads also occurred in Kirksville, inundating vehicles and stranding drivers.[35] Gerald received nearly 4 inches (100 mm) in 30 minutes according to the Gerald-Rosebud Fire Protection District, flooding basements and cars and prompting a water rescue.[36] U.S. Route 50 was flooded.[36]

In Alabama, roads, including U.S. Route 231 and Alabama State Route 75,[37] in Oneonta were flooded, forcing emergency management to rescue several people from their cars.[28] Floodwaters also entered businesses in Oneonta.[38]

The Obion County Emergency Management Agency will partner with an agency in Kentucky to provide temporary housing for flood victims.[10] Shelters were opened in Union City, Tennessee as well.[39][40] The Tennessee Highway Patrol assisted with the Obion County Sheriff and Union City law enforcement.[19] Flood recovery efforts also started in Sikeston, Missouri.[41] The Salvation Army responded to the floods, assisting flood victims.[42]