Illinois (Chicago)
September
Weather in Illinois for September 2026
Your guide to Illinois weather in September - trends and predictions
In general, the average temperature in Illinois at the beginning of September is 25.4 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 21.9 °F by the end of September.
The climate of Illinois in September is notably wet, with an average of 13 rainy days, and a total of 71.9 mm of precipitation.
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Temperatures
Rain 🌧️
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17
Dry days
13
Rainy days
0
Snow days
24°/17°
Temperatures
19 km/h
Avg max wind
64 %
Avg humidity
Illinois Weather September
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What’s the Weather Like in Illinois This September?
Discover the average temperatures and weather trends across Illinois’s cities this September.
Temperatures trend during September in Illinois
See the weather trend as well as the moving average line
September weather in Illinois day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Sunny | 26° /18° | 0 mm | 6 | |
| Sept. 2 |  Partly cloudy | 26° /19° | 0 mm | 6 | |
| Sept. 3 |  Moderate rain at times | 27° /17° | 8.4 mm | 6 | |
| Sept. 4 | Moderate rain at times | 25° /18° | 0.4 mm | 6 | |
| Sept. 5 | Sunny | 27° /18° | 0.2 mm | 6 | |
| Sept. 6 |  Patchy rain possible | 24° /17° | 2.3 mm | 6 | |
| Sept. 7 | Patchy rain possible | 23° /15° | 3 mm | 5 | |
| Sept. 8 | Sunny | 24° /15° | 0 mm | 6 | |
| Sept. 9 | Sunny | 25° /16° | 0 mm | 6 | |
| Sept. 10 | Sunny | 26° /17° | 0 mm | 6 | |
| Sept. 11 |  Cloudy | 25° /17° | 20.3 mm | 6 | |
| Sept. 12 | Partly cloudy | 23° /16° | 0.1 mm | 5 | |
| Sept. 13 | Light rain shower | 25° /17° | 2.2 mm | 5 | |
| Sept. 14 | Sunny | 25° /18° | 0.6 mm | 6 | |
| Sept. 15 | Cloudy | 27° /18° | 0 mm | 6 | |
| Sept. 16 | Sunny | 26° /18° | 0.5 mm | 6 | |
| Sept. 17 | Partly cloudy | 25° /18° | 0.5 mm | 6 | |
| Sept. 18 | Cloudy | 24° /17° | 0.8 mm | 5 | |
| Sept. 19 | Patchy rain possible | 24° /17° | 4.4 mm | 5 | |
| Sept. 20 |  Thundery outbreaks possible | 27° /18° | 4 mm | 6 | |
| Sept. 21 | Moderate or heavy rain shower | 24° /18° | 3.6 mm | 6 | |
| Sept. 22 | Patchy rain possible | 22° /16° | 10 mm | 5 | |
| Sept. 23 | Patchy rain possible | 20° /15° | 1 mm | 5 | |
| Sept. 24 |  Overcast | 22° /15° | 2.1 mm | 5 | |
| Sept. 25 | Overcast | 22° /15° | 0.6 mm | 5 | |
| Sept. 26 |  Mist | 23° /14° | 5.1 mm | 6 | |
| Sept. 27 | Sunny | 23° /15° | 1.9 mm | 5 | |
| Sept. 28 | Patchy rain possible | 19° /15° | 0.1 mm | 5 | |
| Sept. 29 | Sunny | 22° /15° | 2.1 mm | 5 | |
| Sept. 30 | Sunny | 22° /16° | 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.
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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?
Moderate rainfall is anticipated in Illinois during September, with a total of 71.9 mm spread over approximately 13 days. Considering plans for rainy days is advisable.
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
Explore the daily rainfall trends and prepare for Illinoiss September weather 💧
UV exposure in Illinois during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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