Climate averages 1991–2020
Iowa City weather
in September.
A warm, wet month: the 4th warmest and the 9th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a warm month in Iowa City: daytime highs average 23.7°C and nights cool to about 14.2°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 99 mm of rain on roughly 8 days, which makes September a wet month (the 9th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 31 min on an average September day.
The nearest other city in this atlas is Cedar Rapids (40 km away). In September its highs average 23.2°C, 0.5°C cooler than Iowa City, with 100 mm of rain.
Among the 498 cities listed in the United States, Iowa City ranks joint 374th of 498 for the warmest September highs and joint 387th of 498 for the driest September (rainfall, lowest first). The mean September high of those 498 cities is 26.9°C; Iowa City is 3.2°C cooler than that mean.
From September to October, average highs fall by 7.1°C to 16.6°C, and monthly rainfall falls from 99 mm to 74 mm.
The annual picture
September in context
Monthly precipitation
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Iowa City climate table
| Month | Average highHigh / low | Average low | Precipitation mm/month | Wet days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | -1.5°C-10.3°C | -10.3°C | 39 | 7.1 | 9.510 h |
| February | 1.1°C-8.2°C | -8.2°C | 46 | 6.5 | 10.611 h |
| March | 8.7°C-1.7°C | -1.7°C | 69 | 9.1 | 11.912 h |
| April | 15.5°C4.9°C | 4.9°C | 111 | 11.8 | 13.313 h |
| May | 21.4°C11.4°C | 11.4°C | 123 | 13.4 | 14.515 h |
| June | 26.3°C17.0°C | 17.0°C | 128 | 11.7 | 15.115 h |
| July | 28.2°C19.3°C | 19.3°C | 95 | 9.5 | 14.915 h |
| August | 27.4°C18.4°C | 18.4°C | 96 | 9.1 | 13.914 h |
| September, selected | 23.7°C14.2°C | 14.2°C | 99 | 8.1 | 12.513 h |
| October | 16.6°C7.6°C | 7.6°C | 74 | 8.6 | 11.111 h |
| November | 8.7°C0.3°C | 0.3°C | 59 | 7.6 | 9.910 h |
| December | 1.4°C-6.3°C | -6.3°C | 49 | 6.9 | 9.29 h |
Precipitation (rain or snow, as water) is the average of the 30 separate monthly totals. A wet day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Cedar Rapids in SeptemberUnited States · 40 kmHigh 23.2°C · Low 13.7°C · 100 mm rain
- Davenport in SeptemberUnited States · 81 kmHigh 23.8°C · Low 14.8°C · 88 mm rain
- Des Moines in SeptemberUnited States · 173 kmHigh 23.9°C · Low 14.3°C · 90 mm rain
- Peoria (Illinois), United States in SeptemberUnited States · 195 kmHigh 24.4°C · Low 15.4°C · 76 mm rain
- Rockford in SeptemberUnited States · 213 kmHigh 22.8°C · Low 13.7°C · 84 mm rain
- Madison in SeptemberUnited States · 235 kmHigh 22.1°C · Low 13.1°C · 84 mm rain
- Bloomington (Illinois), United States in SeptemberUnited States · 250 kmHigh 24.3°C · Low 14.8°C · 77 mm rain
- Springfield (Illinois), United States in SeptemberUnited States · 261 kmHigh 25.2°C · Low 15.5°C · 80 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Iowa City) is explained once on the Iowa City year overview and on the Sources, method and limits page.