July 26th, 2022: Historic Flash Flooding in St. Louis
St. Louis saw more rain in one day than any other in its history, causing widespread damage and two deaths.
The meteorology behind July 25th's catastrophic flash flooding
Radar loop from KLSX in Weldon Spring starting at 9:00pm on July 25th. Notice the persistent thunderstorms impacting much of the St. Louis Metropolitan Area.
A persistent series of thunderstorms developed around 9 pm on July 25th across central Missouri. The areal extent of the training thunderstorms expanded through the late evening and by around 11 pm were impacting the St. Louis metropolitan area. Rain continuously fell at St. Louis-Lambert International Airport from 11 pm until 2 pm on the 26th.
During that time, instantaneous rainfall rates exceeding 4"/hr were observed and 9.06" of rain fell in that 15 hour period. In one six-hour period, 7.68" of rain fell, which statistically has a 1 in 1000 chance of occurring in a given year. Despite dry conditions prior to the event, rainfall amounts and rates of these magnitudes caused widespread impacts and at least two fatalities.
A conceptual model for the meteorological setup of the flash flooding event that occurred on July 26th, 2022 in the St. Louis metropolitan area. This setup is described in further technical detail in this paper written by Moore et al. (2003) in the AMS Weather and Forecasting journal.
The heavy rain fell north of a stationary front that was anchored across southern Missouri and Illinois. A strong southwesterly low-level jet featuring winds in excess of 50 mph (around 5,000 feet above ground level) brought in copious amounts of low-level moisture which interacted with the front and the upper-level jet stream to produce repeated thunderstorms over the same area for more than 6 hours. These thunderstorms caused a narrow, but intense swath of heavy rainfall: most of the area saw at least a few inches of rainfall with a narrow band of 6 to 12 inches stretching from east central Missouri to southwest Illinois.
St. Louis set a daily rainfall record that previously stood for over 100 years, and the NWS in St. Louis issued its first-ever Flash Flood Emergency.
Flooding impacts were observed across the St. Louis metropolitan area
Road closures, swift water rescues, and inundated train stations are just a few of the ways the historic flash flooding disrupted the morning commute and rattled lives.
Some river levels jumped to moderate or major flood stages
Small stream gauge flood stages across the St. Louis area after the heavy rain on July 25th and July 26th.
Luckily, dry conditions beforehand left river levels very low to start. Despite this, a few gauges measured dramatic rises in a short period of time.
Several smaller rivers and creeks rose to flood stage across the St. Louis metropolitan area.
St. Louis is our home as well. We stand with our community as we recover from this difficult time together.
NWS St. Louis would like to extend our thoughts and condolences to the families of the two men who lost their lives in the flooding. We also hold those who were directly impacted by the flooding in our thoughts.
Finally, we extend our sincere gratitude to the first responders and our core partners in police, fire, EMT, emergency management, and broadcast media for all they did during this event to ensure people were as safe and informed as possible.
