CHICAGO, Illinois — The flash flood threat that battered the Midwest and Ohio Valley overnight is not over yet on Sunday, September 20, 2026, with a continued and active excessive rainfall threat covering a broad zone from Cedar Rapids, Iowa through Chicago, Indianapolis, Columbus, Dayton, Pittsburgh and Cleveland as of 3:15 AM CDT Sunday. Ongoing morning showers tracking out of southeastern Iowa and northern Missouri are keeping the flash flood risk active early today, and with grounds already highly compromised from overnight storms, any additional rainfall could cause localized flooding before the threat slowly tapers from west to east by early afternoon. Fueled by a deep plume of atmospheric moisture, repeating storms could drop localized totals of 2 to 5 inches on top of what has already fallen — a combination that brings a strong potential for dangerous flash flooding across the Ohio Valley today.
Two Separate Flooding Threats Active This Morning
The source data identifies two distinct areas of concern driving today’s continued flash flood threat across the Midwest and Ohio Valley:
Western Threat — Southeastern Iowa and Northern Missouri:
- Ongoing morning showers tracking out of southeastern Iowa and northern Missouri are keeping the flash flood risk active across the western portion of the threat zone early this Sunday morning.
- Cedar Rapids, Iowa sits on the western edge of the Slight Risk zone on the Sunday, September 20 excessive rainfall outlook, with the ground already saturated from overnight storms and any additional rainfall capable of triggering localized flooding.
- St. Louis, Missouri falls within the broader rainfall environment on today’s excessive rainfall outlook, sitting on the southwestern edge of the active moisture zone through early afternoon Sunday.
- The western flash flood threat is expected to slowly taper from west to east by early afternoon as the morning showers gradually shift eastward and lose intensity.
Eastern Threat — Ohio River and West Virginia Redevelopment:
- A separate area of morning rain is moving toward the higher terrain of West Virginia and will briefly weaken by late morning along the Ohio River corridor.
- However, new rounds of moderate to heavy rainfall are expected to redevelop later in the day across the Ohio Valley, fueled by a deep plume of atmospheric moisture that continues feeding the storm system.
- This redevelopment means the flash flood threat does not simply end once the morning rain weakens — a second round of heavy rainfall will reignite flooding concerns across Columbus, Dayton, Cincinnati, Pittsburgh and Cleveland later Sunday.
Cities Inside the Slight Risk Excessive Rainfall Zone Sunday
The Slight Risk zone, representing a 15 percent or greater chance of excessive rainfall capable of causing flash flooding, covers the following cities on the Sunday, September 20, 2026 excessive rainfall outlook:
- Cedar Rapids, Iowa sits on the western edge of the Slight Risk zone for Sunday, confirming eastern Iowa remains in the excessive rainfall threat area through today.
- Chicago, Illinois falls within the Slight Risk zone on the Sunday, September 20 excessive rainfall outlook, continuing the multi-day flooding threat for the metro area.
- Indianapolis, Indiana is visible within the Slight Risk zone on today’s excessive rainfall map, with repeating storm rounds capable of producing 2 to 5 inch localized totals on already saturated ground.
- Columbus, Ohio and Dayton, Ohio fall within the Slight Risk zone on the Sunday excessive rainfall outlook, placing these major Ohio cities in the path of both the morning rain and the expected afternoon redevelopment.
- Cincinnati, Ohio is visible within the Slight Risk zone on today’s map, at risk from the deep atmospheric moisture plume driving repeating storm rounds across the Ohio Valley.
- Cleveland, Ohio falls within the Slight Risk zone on the Sunday, September 20 excessive rainfall outlook on the northeastern edge of the risk area.
- Pittsburgh, Pennsylvania is visible within the Slight Risk zone on today’s map, with the flash flood threat extending into western Pennsylvania as the heavy rain shifts eastward through Sunday.
Cities Inside the Marginal Risk Zone Sunday
The broader Marginal Risk zone, representing a 5 percent chance of isolated flash flooding, extends the excessive rainfall threat footprint outward from the Slight Risk core to include:
- Winston-Salem, North Carolina is visible on the southeastern edge of the Marginal Risk zone on today’s excessive rainfall outlook, confirming the moisture plume’s influence extends into the Carolinas through Sunday.
- The broader Marginal Risk area covers additional communities across Indiana, Ohio, Pennsylvania and the Ohio Valley corridor surrounding the primary Slight Risk zone through Sunday, September 20, 2026.
Why Saturated Ground Makes 2 to 5 More Inches So Dangerous Today
The source data uses precise and serious language — the soil is already highly compromised from prior rainfall. This is not a minor qualifier. When soil reaches a highly compromised saturation state, it functions essentially like pavement — rain runs off the surface immediately rather than soaking in. The 2 to 5 inch localized totals possible today from repeating storm rounds falling on highly compromised ground across Chicago, Indianapolis, Columbus and Pittsburgh will produce runoff rates and flooding responses far more severe than the same rainfall totals would generate on dry soil. Stream rises will be rapid, urban flooding will develop quickly and road conditions can deteriorate from passable to dangerous in a matter of minutes during the heaviest rainfall rates today.
When Does the Threat Begin Tapering Off
The western portion of the flash flood threat begins tapering from west to east by early afternoon Sunday, September 20, 2026, as the morning showers shift eastward and weaken. However, the eastern portion of the threat along the Ohio River and West Virginia terrain is expected to see new storm development later in the day, meaning the overall flash flood risk across the Ohio Valley does not completely end until the redevelopment rounds also move through the region. Residents across Columbus, Dayton, Pittsburgh and Cleveland should not assume the afternoon tapering of the western threat means the danger is completely over — monitor radar and weather alerts closely through Sunday evening.
