OMAHA, NEBRASKA — Forecasters at the NWS Weather Prediction Center are warning that heavy rain could lead to flash flooding across parts of the Southwest and Midwest today, Tuesday, September 15, with an Excessive Rainfall Forecast placing a Moderate Risk over a small portion of eastern Nebraska and western Iowa. A much broader Slight Risk stretches from the Southwest into the Midwest, covering a long diagonal corridor that reaches from New Mexico and Texas through Oklahoma, Kansas, Missouri and Illinois. Forecasters are urging residents across the outlined zones to stay weather aware and never drive through flooded roads.
Moderate Risk Targets Small Portion of Eastern Nebraska and Western Iowa
The highest-end risk category on today’s map is confined to a small, localized zone straddling the eastern Nebraska and western Iowa border, where the NWS Weather Prediction Center has placed a Moderate Risk for excessive rainfall. That designation represents the second-highest tier on the agency’s four-level scale and signals forecasters have higher confidence that rainfall rates and totals in that specific pocket could be intense enough to overwhelm drainage and trigger flash flooding, even though the affected area itself remains relatively compact compared to the broader Slight and Marginal zones surrounding it.
Broader Slight Risk Stretches From the Southwest Into the Midwest
Surrounding the Moderate Risk pocket, a much larger Slight Risk zone extends in a long diagonal band from the desert Southwest all the way into the Midwest. On today’s map, that yellow-shaded corridor begins across parts of New Mexico and the Texas Panhandle, continues through Oklahoma and Kansas, and pushes into Missouri before narrowing as it approaches Illinois. Communities inside this zone face a real, if lower, chance of seeing flash flooding develop from locally heavy downpours, particularly where slower-moving storm cells allow rain to accumulate over the same areas.
Marginal Risk Extends From New Mexico to the Great Lakes
The outermost and lowest tier on today’s outlook, the Marginal Risk category, covers by far the largest footprint on the map. That green-shaded zone begins across much of New Mexico and west Texas, wraps around the Slight and Moderate zones through the southern and central Plains, and then stretches northeast across Missouri, Illinois and Wisconsin before reaching toward the Great Lakes near Michigan. While a Marginal Risk reflects a lower overall probability of excessive rainfall, forecasters note that isolated, localized flash flooding remains possible anywhere thunderstorms manage to stall or repeatedly redevelop over the same communities within that broad corridor.
How the NWS Weather Prediction Center’s Four-Tier Risk Scale Works
Today’s outlook draws on the NWS Weather Prediction Center’s standard four-category scale for excessive rainfall, ranging from Marginal and Slight up through Moderate and, at the top end, High. No areas were placed in the High Risk category on today’s map, meaning eastern Nebraska and western Iowa’s Moderate Risk zone represents the most significant flash flooding concern nationwide for Tuesday, September 15. Forecasters use this tiered system to help local National Weather Service offices and emergency managers prioritize where the greatest attention and resources should be focused as storms develop through the day.
Southwest Moisture Feeding Midwest Storms Raises Flash Flooding Concerns
The long, diagonal shape of today’s risk corridor, stretching from the Southwest through the Midwest, points to a plume of moisture streaming northeastward and interacting with a developing storm system capable of producing heavy rain across multiple states in a single day. When that kind of moisture feed lines up with slow-moving or repeatedly redeveloping thunderstorms, forecasters say the risk of flash flooding rises sharply, since rainfall can accumulate far faster than soils and urban drainage systems are able to absorb it, particularly across the more compact Moderate Risk zone near the Nebraska-Iowa border.
Never Drive Through Flooded Roads as Rain Threat Continues Today
With flash flooding possible across such a wide stretch of the country today, forecasters are repeating one of the most important safety reminders tied to any excessive rainfall event: never attempt to drive through a flooded roadway. Water depth over a road is often impossible to judge from behind the wheel, and even a relatively small amount of fast-moving water can sweep a vehicle off the roadway. Residents across the Southwest and Midwest, and especially within today’s Moderate Risk zone near eastern Nebraska and western Iowa, are being urged to stay weather aware through the afternoon and evening as today’s rainfall threat unfolds.
