Flash Flood in Madison County, Missouri

Between 6 and 7 inches of rain fell in about a 2 to 3 hour period across northern portions of Madison County. Numerous creeks flooded, including Saline Creek in Fredericktown. Also, several rivers flooded including Little St. Francois River in Fredericktown, which rose 18.6 feet in 5 hours, cresting at 20.49 feet by 715 am. At least 21 people were rescued from the flood waters in and around Fredericktown. One person drove into flood waters on Highway Z on the east side of town and floated into the ditch. They were rescued and sustained no injuries. The flash flooding affected the Holmes Subdivision as well as other homes and businesses along Saline Creek and a creek along South Mine La Motte Avenue.

During the afternoon hours of August 3rd, numerous thunderstorms developed across parts of eastern Missouri and west-central Illinois, triggered by strong surface heating ahead of a surging outflow boundary. These storms developed within a strongly unstable environment, featuring MLCAPE values ranging from 2500 to as much as 4000 J/kg and largely driven by the very warm and humid boundary layer. The initial round of storms struggled to become organized. Eventually cold pool interactions drove upscale growth into a more linear complex. Damaging winds, occasional large hail were reported as well as bursts of very heavy rain rates. By the evening of August 3rd, storms grew upscale, with additional rounds of thunderstorms developing upstream from this initial activity. The primary hazard transitioned from a damaging wind threat to a heavy rain and flash flooding threat, as storms were extremely efficient rain producers. Warm cloud depths were around 4.5km, along with anomalously high precipitable water values of 2 to 2.5 inches, and Corfidi vector orientations that supported westward back-building which enhanced the potential for locally heavy rain, both in terms of instantaneous rates (2+ inches per hour at times) and training of storms. By mid morning on August 4th, widespread rainfall amounts of 1 to 3 inches fell, mainly along and south of I-70 in Missouri and along and east of I-55 in Illinois. Over the St. Louis metro area, as well as Fredericktown, MO, between 4 and 7 inches of rain fell. There were numerous reports of flash flooding in these areas.