Moisture meets a strengthening front
The Weather Prediction Center expected a deepening low-pressure system in the northern Plains to draw Gulf moisture northward ahead of a front. Its 14 September discussion called for widespread showers and thunderstorms from the Rockies through the Plains and Upper Midwest over the following days. Several rounds of rain can create more flooding concern than any one isolated shower, especially where soils are already wet.
Timing matters
The highest-impact corridor may shift as the front and embedded storms develop. A forecast for a large region does not mean every town will receive heavy rain, nor does it prove flooding has occurred. River forecasts, flash-flood watches and local radar updates should be checked separately.
This article describes the weather pattern expected from the 14 September discussion. If a warning is issued, follow the local National Weather Service instructions for that place and time.