Illinois (Chicago)
September
Weather in Illinois for September 2025
Your guide to Illinois weather in September - trends and predictions
In general, the average temperature in Illinois at the beginning of September is 26.7 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 21.7 °F by the end of September.
Illinois sees moderate rainfall in September, averaging 10 rainy days.
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20
Dry days
10
Rainy days
0
Snow days
24°/17°
Temperatures
19 km/h
Avg max wind
68 %
Avg humidity
Illinois in September average weather
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| Mon. | Tue. | Wed. | Thu. | Fri. | Sat. | Sun. |
|---|---|---|---|---|---|---|
| 1  25° | 2  27° | 3 29° | 4 30° | 5  31° | 6 26° | 7 19° |
| 8  21° | 9  25° | 10 26° | 11  25° | 12 23° | 13 23° | 14 23° |
| 15 27° | 16  26° | 17 21° | 18 21° | 19  22° | 20 28° | 21 27° |
| 22  24° | 23 21° | 24 21° | 25 23° | 26  23° | 27 21° | 28 20° |
| 29 21° | 30 23° |
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Temperatures trend during September in Illinois
See the weather trend as well as the moving average line
September weather day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 | Sunny | 25° /17° | 0 mm | 7 | |
| Sept. 2 | Partly cloudy | 27° /18° | 0 mm | 7 | |
| Sept. 3 | Partly cloudy | 29° /17° | 0 mm | 7 | |
| Sept. 4 | Sunny | 30° /19° | 0 mm | 8 | |
| Sept. 5 | Patchy rain possible | 31° /21° | 0.6 mm | 8 | |
| Sept. 6 | Light rain shower | 26° /18° | 5 mm | 6 | |
| Sept. 7 | Patchy rain possible | 19° /13° | 0.3 mm | 5 | |
| Sept. 8 | Overcast | 21° /14° | 0 mm | 6 | |
| Sept. 9 | Cloudy | 25° /16° | 0 mm | 6 | |
| Sept. 10 | Partly cloudy | 26° /17° | 0 mm | 7 | |
| Sept. 11 | Moderate or heavy rain shower | 25° /18° | 28.6 mm | 6 | |
| Sept. 12 | Cloudy | 23° /17° | 0 mm | 6 | |
| Sept. 13 | Light rain shower | 23° /17° | 0.6 mm | 5 | |
| Sept. 14 | Overcast | 23° /17° | 0 mm | 6 | |
| Sept. 15 | Cloudy | 27° /18° | 0 mm | 6 | |
| Sept. 16 | Thundery outbreaks possible | 26° /18° | 1.2 mm | 6 | |
| Sept. 17 | Light rain shower | 21° /16° | 1.2 mm | 5 | |
| Sept. 18 | Cloudy | 21° /16° | 0 mm | 5 | |
| Sept. 19 | Heavy rain | 22° /16° | 10.1 mm | 5 | |
| Sept. 20 | Thundery outbreaks possible | 28° /18° | 0.1 mm | 6 | |
| Sept. 21 | Overcast | 27° /19° | 0 mm | 7 | |
| Sept. 22 | Fog | 24° /17° | 18 mm | 6 | |
| Sept. 23 | Sunny | 21° /16° | 0 mm | 5 | |
| Sept. 24 | Overcast | 21° /15° | 0 mm | 5 | |
| Sept. 25 | Patchy rain possible | 23° /16° | 0.1 mm | 5 | |
| Sept. 26 | Patchy light rain with thunder | 23° /15° | 12.8 mm | 6 | |
| Sept. 27 | Light rain shower | 21° /16° | 4.7 mm | 5 | |
| Sept. 28 | Patchy rain possible | 20° /17° | 0.1 mm | 5 | |
| Sept. 29 | Mist | 21° /17° | 5.3 mm | 5 | |
| Sept. 30 | Fog | 23° /17° | 0 mm | 6 | |
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Important Notice
Our weather forecast for Illinois in September is based on the analysis of historical data rather than real-time forecast models. While this provides a general overview, weather conditions can change. We recommend that you check the Illinois forecast closer to your planned date for the most up-to-date weather information.
Illinois in September - FAQ
What are the expected maximum and minimum temperatures in Illinois during September?
During September, expect a variety of temperatures with highs around 24° and lows near 17°, suitable for diverse activities and preferences.
How much rainfall should be expected in Illinois during September?
Significant rainfall exceeding 127.2 mm is expected in Illinois during September, occurring over more than 10 days. Preparing for wet conditions is recommended in your planning.
What are the typical wind conditions in Illinois during September?
The average wind speed in Illinois during September is 19 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in Illinois
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UV exposure in Illinois during September
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