September is one of the warmer months of the year in Chicago, with average highs near 21.4°C and lows around 15.6°C (mean 18.5°C). It is about average for rainfall, averaging 84 mm of rainfall and 75% relative humidity across the period.
September is one of the warmer months of the year in Chicago. Across 45 years of records, the warmest September in Chicago was 2005 — when the month averaged 21.3°C — while the coldest was 1993 at 15.1°C. Typical September days reach 21.4°C with nights near 15.6°C. The long-term trend is warming, about 0.9°C per decade.
September is about average for rainfall in Chicago, averaging 84 mm of rainfall. The wettest September on record was 2008 with 284 mm, while the driest was 2004 at 15 mm.
Relative humidity in Chicago during September averages 75%. The most humid September was 2019 at 84%, and the least humid was 1999 at 66%.
September receives about 4.3 kWh/m²/day of solar energy in Chicago. The sunniest September was 2004 at 5.2 kWh/m²/day, and the cloudiest was 1993 at 3.3.
Average wind speed in Chicago during September is 4 m/s. The windiest Septembers were 2000 and 2010 at 4.8 m/s, while the calmest was 2025 at 3.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 16.9°C | 17.7°C | 19.0°C | 19.3°C | 20.1°C | +3.2°C |
| Avg High | 20.0°C | 20.6°C | 21.9°C | 22.0°C | 23.0°C | +3°C |
| Avg Low | 13.8°C | 14.8°C | 16.1°C | 16.7°C | 17.2°C | +3.4°C |
| Avg Rain | 95 mm | 78 mm | 94 mm | 84 mm | 65 mm | -30 mm |
September temperatures in Chicago have risen by about 3.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 5.2°C (1985) to a record high of 30.7°C (2011).
Rainfall in September is about average for rainfall, averaging 84 mm, with a wettest year of 284 mm.
One of the best times to visit Chicago
September is one of the best times to visit Chicago. Expect days averaging 21.4°C and nights around 15.6°C (mean 18.5°C) — warmer than Chicago's yearly average — with higher rainfall (84 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 23.4°C | 20.3°C | 17.3°C | 28.0°C | 12.5°C | 37 mm | 71% | 3.1 m/s | 5 |
| 2024 | 24.2°C | 21.1°C | 18.1°C | 28.6°C | 14.1°C | 53 mm | 67% | 3.7 m/s | 4.8 |
| 2023 | 22.4°C | 19.9°C | 17.5°C | 29.4°C | 15.6°C | 93 mm | 75% | 3.6 m/s | 4 |
| 2022 | 22.3°C | 19.5°C | 16.8°C | 28.1°C | 11.7°C | 85 mm | 75% | 3.9 m/s | 4.4 |
| 2021 | 24.1°C | 20.9°C | 17.8°C | 28.3°C | 12.6°C | 41 mm | 71% | 4.5 m/s | 4.6 |
| 2020 | 21.6°C | 18.7°C | 15.7°C | 28.7°C | 10.9°C | 80 mm | 76% | 4.7 m/s | 4.1 |
| 2019 | 22.5°C | 20.0°C | 17.5°C | 26.2°C | 14.6°C | 208 mm | 84% | 3.8 m/s | 3.8 |
| 2018 | 22.5°C | 20.0°C | 17.5°C | 29.0°C | 10.8°C | 81 mm | 79% | 3.9 m/s | 4.4 |
| 2017 | 23.0°C | 20.1°C | 17.2°C | 30.0°C | 13.5°C | 24 mm | 72% | 3.6 m/s | 4.8 |
| 2016 | 23.2°C | 20.9°C | 18.5°C | 28.2°C | 12.7°C | 60 mm | 79% | 4.3 m/s | 4.4 |
| 2015 | 23.0°C | 20.3°C | 17.6°C | 28.6°C | 13.3°C | 106 mm | 79% | 3.8 m/s | 4.4 |
| 2014 | 20.6°C | 17.7°C | 14.8°C | 26.5°C | 9.5°C | 77 mm | 79% | 3.6 m/s | 4.4 |
| 2013 | 22.2°C | 19.5°C | 16.7°C | 29.9°C | 12.9°C | 65 mm | 75% | 3.9 m/s | 4.7 |
| 2012 | 21.4°C | 18.5°C | 15.7°C | 27.7°C | 9.4°C | 54 mm | 72% | 4.2 m/s | 4.7 |
| 2011 | 19.8°C | 17.7°C | 15.6°C | 30.7°C | 10.7°C | 93 mm | 76% | 4.5 m/s | 3.9 |
| 2010 | 21.3°C | 18.7°C | 16.2°C | 26.9°C | 12.9°C | 71 mm | 75% | 4.8 m/s | 4.3 |
| 2009 | 20.8°C | 18.6°C | 16.5°C | 25.3°C | 10.3°C | 25 mm | 80% | 3.3 m/s | 4.3 |
| 2008 🌧️ | 21.9°C | 19.4°C | 16.8°C | 29.8°C | 12.9°C | 284 mm | 80% | 3.7 m/s | 3.9 |
| 2007 | 22.5°C | 19.4°C | 16.3°C | 27.9°C | 10.0°C | 41 mm | 76% | 4.3 m/s | 5.1 |
| 2006 | 20.2°C | 17.7°C | 15.2°C | 25.8°C | 10.4°C | 122 mm | 78% | 4.3 m/s | 3.8 |
| 2005 🔥 | 24.4°C | 21.3°C | 18.2°C | 29.8°C | 10.2°C | 67 mm | 71% | 4.2 m/s | 4.4 |
| 2004 | 23.0°C | 20.1°C | 17.1°C | 26.6°C | 14.2°C | 15 mm | 73% | 3.8 m/s | 5.2 |
| 2003 | 21.0°C | 17.8°C | 14.6°C | 26.9°C | 8.0°C | 54 mm | 73% | 4.2 m/s | 4.5 |
| 2002 | 23.2°C | 19.9°C | 16.6°C | 28.9°C | 9.4°C | 74 mm | 72% | 3.5 m/s | 4.7 |
| 2001 | 19.7°C | 17.1°C | 14.5°C | 26.0°C | 9.1°C | 114 mm | 78% | 4.3 m/s | 4.4 |
| 2000 | 21.8°C | 18.6°C | 15.5°C | 29.5°C | 10.2°C | 141 mm | 73% | 4.8 m/s | 4.1 |
| 1999 | 22.1°C | 18.7°C | 15.2°C | 30.5°C | 9.0°C | 66 mm | 66% | 4.3 m/s | 4.9 |
| 1998 | 23.8°C | 20.9°C | 18.0°C | 29.5°C | 13.3°C | 68 mm | 71% | 3.9 m/s | 4.4 |
| 1997 | 21.0°C | 18.2°C | 15.5°C | 26.2°C | 12.1°C | 66 mm | 75% | 4.3 m/s | 4.4 |
| 1996 | 20.2°C | 17.7°C | 15.2°C | 25.3°C | 9.3°C | 89 mm | 78% | 3.8 m/s | 4.1 |
| 1995 | 19.9°C | 16.8°C | 13.6°C | 27.3°C | 5.7°C | 39 mm | 69% | 4.1 m/s | 4.4 |
| 1994 | 21.0°C | 17.7°C | 14.5°C | 26.8°C | 9.5°C | 47 mm | 76% | 3.4 m/s | 4.1 |
| 1993 ❄️ | 17.3°C | 15.1°C | 12.9°C | 22.3°C | 7.0°C | 140 mm | 80% | 4.2 m/s | 3.3 |
| 1992 | 19.6°C | 16.5°C | 13.5°C | 24.6°C | 8.2°C | 133 mm | 78% | 4.2 m/s | 4 |
| 1991 | 20.4°C | 17.4°C | 14.4°C | 27.5°C | 7.7°C | 76 mm | 71% | 3.9 m/s | 4.4 |
| 1990 | 20.7°C | 17.9°C | 15.1°C | 27.8°C | 7.2°C | 59 mm | 79% | 4.1 m/s | 4.2 |
| 1989 | 19.1°C | 16.4°C | 13.6°C | 24.3°C | 7.3°C | 73 mm | 76% | 3.7 m/s | 4.4 |
| 1988 | 21.6°C | 17.8°C | 14.0°C | 25.6°C | 10.9°C | 65 mm | 71% | 3.9 m/s | 4.1 |
| 1987 | 20.1°C | 17.4°C | 14.7°C | 24.9°C | 11.2°C | 62 mm | 81% | 3.5 m/s | 3.9 |
| 1986 | 20.2°C | 17.3°C | 14.3°C | 24.6°C | 11.0°C | 215 mm | 81% | 3.8 m/s | 3.7 |
| 1985 | 19.8°C | 16.7°C | 13.6°C | 27.5°C | 5.2°C | 67 mm | 77% | 4.2 m/s | 3.8 |
| 1984 | 19.1°C | 15.8°C | 12.5°C | 25.1°C | 6.2°C | 100 mm | 74% | 4 m/s | 3.6 |
| 1983 | 20.6°C | 17.1°C | 13.5°C | 27.6°C | 7.3°C | 108 mm | 73% | 4 m/s | — |
| 1982 | 19.6°C | 16.5°C | 13.3°C | 24.2°C | 9.9°C | 54 mm | 79% | 3.7 m/s | — |
| 1981 | 19.8°C | 17.3°C | 14.7°C | 24.9°C | 8.9°C | 112 mm | 77% | 4.4 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 21.4°C with lows near 15.6°C (mean 18.5°C), based on 45 years of NASA POWER data.
September averages 84 mm of rainfall in Chicago, about average for rainfall. The wettest on record was 284 mm in 2008.
The hottest September reached 30.7°C in 2011. The coldest dipped to 5.2°C in 1985.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 3.6°C. Daytime highs moved from 19.8°C to 23.3°C and overnight lows from 13.5°C to 17.5°C over the same span.
September is one of the warmer months of the year in Chicago and about average for rainfall, so plan for around 21.4°C daytime highs and 15.6°C at night.
Not quite — September is the 10th coolest month in Chicago, averaging 18.5°C.
For September in Chicago, pack light layers you can adjust through the day, with typical highs of 21.4°C and lows of 15.6°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 75% — quite humid.
Average wind speed in September is 4 m/s. The windiest September on record averaged 4.8 m/s (2000).
The wettest September on record was 2008 with 284 mm. On average, September sees 84 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Chicago behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
