Monthly Weather Report

Iowa Monthly Weather Summary – September 2026

General Summary

Iowa’s statewide temperatures averaged 68.3 degrees or 4.6 degrees above normal while precipitation totaled 7.83 inches or 4.35 inches above normal. September 2026 ranks as the 9th warmest and 4th wettest in 154 years of statewide records. September 2015 was warmer while 2018 wetter and the 3rd wettest.

Temperatures

Statewide average temperatures in September were above average across all of Iowa with the warmest conditions found over the southern two tier of counties. While daytime highs were above-normal, nocturnal cloud cover held overnight lows anywhere from five to 12 degrees above normal. September’s statewide average maximum temperature was 76.3.3 degrees, 0.9 degree above normal, while the average minimum temperature was 60.2 degrees, 8.3 degrees above normal. Donnelson (Lee County) and Lamoni (Decatur County) reported the month’s high temperature of 100 degrees on the 1st and 3rd, respectively, on average eight degrees above normal. Mason City Municipal Airport (Cerro Gordo County) reported the month’s low temperature of 42 degrees from the 23rd, four degrees below normal.

Cooling Degree Days

Home air conditioning requirements, as estimated by cooling degree day totals, averaged 20% more than last September and 60% more than normal. Cooling degree day totals since January are running on par with last year at this time and 22% more than normal.

Precipitation

Portions of west-central, central and eastern Iowa experience significant wetness during September with stations collecting more rainfall than May and June, climatologically the two wettest months for the state. Des Moines (Pol County) recorded its second wettest September and third wettest month of any month. Belle Plaine (Benton County) and Iowa City (Johnson County), with periods of record going back to 1893, had their wettest September on record. Only pockets of north-central and southeast Iowa reported near-normal amounts. Monthly precipitation totals ranged from 2.87 inches at Keokuk Lock and Dam (Lee County) to 15.42 inches in Ainsworth (Washington County).

September 2026 was an exceptionally wet month across Iowa, characterized by frequent rounds of showers and thunderstorms that produced widespread heavy rainfall, localized flash flooding and significant rainfall accumulations. A persistent upper-level ridge over the southern United States helped focus multiple disturbances and surface boundaries across the state, while abundant Gulf moisture and mid-level Pacific monsoonal moisture contributed to unusually high atmospheric moisture content. The most significant rainfall events occurred from September 13–15 and 18–20. During the first event, much of southern Iowa received at least 2.00 inches, with a corridor from Council Bluffs (Pottawattamie County) to Des Moines reporting 3.00 to 5.00 inches and localized totals exceeding 6.00 inches in west-central Iowa. Training thunderstorms also produced several inches of rainfall across the Des Moines metropolitan area. The second event concentrated heavy rainfall over eastern Iowa, where nearly 60 stations measured at least 4.00 inches, including 6.75 inches in North Liberty (Johnson County). The prolonged rainfall resulted in numerous flash flood warnings and significant flooding impacts.

The wet pattern continued through the final third of September as successive low pressure systems and associated disturbances generated additional widespread rainfall. From September 21–27, repeated rounds of showers produced generally moderate accumulations, with locally heavier totals exceeding 2.00 inches in western Iowa. Another widespread event on September 29–30 brought 0.50 to 1.50 inches to much of southern Iowa, followed by a more intense rainfall episode late on the 30th that extended into early October. This system produced widespread 2.00- to 4.00-inch totals across portions of western and northern Iowa, with localized amounts exceeding 5.00 inches in Harrison County. The persistent rainfall, particularly during the second half of the month, limited opportunities for soils to dry and contributed to increasingly saturated conditions across much of the state. Overall, September's precipitation pattern was notable for its frequency, geographic extent and repeated high-intensity rainfall events, creating unfavorable field conditions and increasing concerns about delayed harvest activities and grain quality

Severe Weather

Severe weather accompanied several rounds of thunderstorms across Iowa during September 2026, particularly during the first half of the month. The most significant severe weather episode began during the evening of September 1, when strong to severe thunderstorms moved into northwestern Iowa before progressing eastward. Several storms prompted tornado warnings, although no tornadoes were observed. Damaging straight-line winds were the primary hazard, with measured gusts reaching 81 mph in Hawarden (Sioux County) and 87 mph in Britt (Hancock County). Additional severe thunderstorms developed along the Iowa-Wisconsin border on September 4, producing large hail and gusty winds. Another organized thunderstorm complex moved into northwestern Iowa early on September 5, bringing locally heavy rainfall.

During the middle and latter portions of September, the primary thunderstorm hazard shifted from damaging winds and hail to excessive rainfall and flash flooding. A favorable combination of strong atmospheric instability, wind shear and abundant moisture supported severe thunderstorm development September 13–15, prompting a Tornado Watch across southwestern Iowa on September 14. However, limited daytime heating reduced the tornado threat as a line of severe thunderstorms advanced into central Iowa. Repeated thunderstorms produced intense rainfall rates and localized flooding, particularly across the Des Moines metropolitan area. Additional rounds of heavy thunderstorms September 18–20 generated numerous flash flood warnings across eastern Iowa, while another intense rainfall event late on September 30 prompted flash flood warnings in western Iowa. Overall, September's severe weather was characterized by an early-month emphasis on damaging winds and large hail, followed by repeated episodes of excessive rainfall and flash flooding as the dominant hazards during the second half of the month.

US Drought Monitor

As of the beginning of September Moderate Drought (D1) covered 19% of the state with a small pocket of embedded D2 (Severe Drought) in northwest Iowa. Exceedingly wet conditions through the month led to the removal of all drought by the last map published on September 29th. Abnormal dryness (D0) held on across pockets of northern Iowa into the first week of October, though covering only 1.4% of the state. 

Justin Glisan, Ph.D.
State Climatologist of Iowa
Iowa Dept. of Agriculture & Land Stewardship
Hoover State Office Bldg.
Des Moines, IA 50319
Telephone: (515) 281-8981
E-mail: [email protected]

WEATHER BY DISTRICTS

* Departures are computed from 1991-2020 normals.                                        
The weather data in this report are based upon information collected by the U. S. Dept. of Commerce, NOAA National Weather Service.