Chicago weather in September
In September, Chicago has daytime highs averaging 23 °C, nights around 16 °C, with 8.8 wet days. Figures are 1991–2020 climate normals.
- 23.2°C Average high
- 16.1°C Average low
- 8.8days Wet days
- 79mm Rainfall
- 13h Daylight
Daily temperatures through September
How September develops
Averages for the first, middle and last part of the month, from daily 1991–2020 normals. Chance of rain is the share of years in which that calendar day recorded more than 1 mm.
| Days | Avg high | Avg low | Chance of rain |
|---|---|---|---|
| 1–10 September | 25.4 °C | 18.3 °C | 31 % |
| 11–20 September | 23.5 °C | 16.2 °C | 28 % |
| 21–30 September | 21.0 °C | 13.9 °C | 29 % |
- Average highs fall from 25.4 °C early in September to 21.0 °C by the end of it.
What to expect
| Measure | Typical September | Share of the month |
|---|---|---|
| Days above 25 °C | 11 of 30 | 36 % |
| Days above 30 °C | 1.8 of 30 | 6 % |
| Days below 0 °C | 0 of 30 | 0 % |
| Days with more than 1 mm rain | 8.8 of 30 | 29 % |
Conditions in September
| Measure | Average |
|---|---|
| Mean temperature | 19 °C |
| Record high (1991–2020) | 34 °C |
| Record low (1991–2020) | 3.8 °C |
| Relative humidity | 70 % |
| Wind speed | 20 km/h |
| Cloud cover | 48 % |
Where Chicago ranks in September
| Ranking | Position | Value |
|---|---|---|
| Places with the best weather in North America in September | 47thof 50 | 89/100 |
September compared with the months around it
| Month | Avg high | Rainfall | Cloud |
|---|---|---|---|
| July | 27.9 °C | 99 mm | 50 % |
| August | 26.9 °C | 98 mm | 50 % |
| September | 23.2 °C | 79 mm | 48 % |
| October | 16.4 °C | 86 mm | 56 % |
| November | 8.8 °C | 72 mm | 63 % |
See all twelve months for Chicago
- September is the 4th warmest month here.
- It is the 6th driest month of the year.
- It ranks 1st for least cloud cover.
- Days last about 13 hours from sunrise to sunset.
- It rains on 8.8 of 30 days — 29 % of the month.
- Nights are about 7.2 °C cooler than the middle of the day.
- The hottest September day on record since 1991 reached 34 °C, 11 °C above the usual daytime high.
QuestionsSeptember in Chicago, answered
How warm is Chicago in September?
Daily highs average 23 °C and nights fall to about 16 °C, a spread of 7.2 °C between afternoon and dawn. That makes September the 4th warmest month of the year here.
Does it rain much in Chicago in September?
September averages 79 mm of rain, spread over about 9 of the 30 days — 29 % of the month. Cloud cover averages 48 % of the sky.
How long are the days in September?
Chicago averages 13 hours between sunrise and sunset in September. Day length is computed from latitude and date, so it is exact rather than modelled — but it says nothing about how much of that time is sunny.
Data sources and method
- ERA5 / ERA5-Land reanalysis — Copernicus Climate Change Service (C3S), ECMWF. Copernicus Licence
- Open-Meteo — Open-Meteo.com. CC BY 4.0
- NOAA OISST v2.1 — NOAA Physical Sciences Laboratory. Public domain
- GeoNames — GeoNames.org. CC BY 4.0
- Normal period
- 1991–2020
- Dataset version
- era5-1991-2020-scores1.1
- Last processed
Measured values come from ERA5 reanalysis and are reproduced unchanged. Calculated by us: daylight hours, beach and comfort scores, monthly rankings, threshold day counts, chance of a wet day by date, ten-day averages within the month. Full formulas are on the methodology page.
Contains modified Copernicus Climate Change Service information 2026. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.