The featured chart is perhaps "Exhibit A" as to why Iowa continues to see heavy rainfall events this September. The chart shows average precipitable water during the month of September based on evening soundings from the Omaha area. This value represents the amount of water within the atmosphere and is expressed by a depth (plotted in millimeters). You can sort of think of the value as the amount of rain that would fall if all of the water was squeezed out of the atmosphere. While the 2026 value still has two weeks of time to pull the average lower, the plotted value is well beyond any previous September on record for the site. Storms that develop within an atmosphere loaded with water vapor are able to efficiently produce rainfall due to limited dry air and typically warmer cloud depths. Multiple rounds of such storms are expected on Friday and into the weekend.