Decatur (IL)
September
Weather in Decatur, Illinois for September 2026
Your guide to Decatur weather in September - trends and predictions
So far, September 2026 in Decatur shows a warmer trend than usual by 2.4 °F.
The forecast for the next days in Decatur predicts temperatures to be around 21 °F, close to the historical average.
In general, the average temperature in Decatur at the beginning of September is 28.4 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 20.9 °F by the end of September.
Decatur experiences moderate rainfall in September, with an average of 7 rainy days and a total precipitation of 198.9 mm.
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Temperatures
Rain 🌧️
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23
Dry days
7
Rainy days
0
Snow days
27°/14°
Temperatures
17 km/h
Avg max wind
65 %
Avg humidity
Decatur Weather September
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Temperatures trend during September in Decatur
See the weather trend as well as the moving average line
September weather in Decatur day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Sunny | 31° /16° | 0 mm | 7 | |
| Sept. 2 | Sunny | 30° /15° | 0 mm | 7 | |
| Sept. 3 |  Overcast | 29° /16° | 0 mm | 6 | |
| Sept. 4 | Sunny | 30° /15° | 1.7 mm | 7 | |
| Sept. 5 | Sunny | 29° /17° | 0 mm | 7 | |
| Sept. 6 |  Mist | 26° /12° | 0.1 mm | 6 | |
| Sept. 7 | Sunny | 24° /9° | 0 mm | 7 | |
| Sept. 8 | Sunny | 26° /9° | 0 mm | 6 | |
| Sept. 9 | Overcast | 27° /13° | 0 mm | 6 | |
| Sept. 10 | Sunny | 28° /14° | 13.7 mm | 5 | |
| Sept. 11 | Sunny | 31° /15° | 0 mm | 6 | |
| Sept. 12 | Overcast | 31° /16° | 0 mm | 7 | |
| Sept. 13 |  Light rain | 29° /17° | 0.5 mm | 6 | |
| Sept. 14 |  Partly cloudy | 32° /16° | 0 mm | 8 | |
| Sept. 15 |  Patchy rain possible | 33° /20° | 0.9 mm | 6 | |
| Sept. 16 | Sunny | 32° /18° | 3.8 mm | 6 | |
| Sept. 17 |  Cloudy | 31° /17° | 0.1 mm | 7 | |
| Sept. 18 | Sunny | 29° /16° | 2.4 mm | 5 | |
| Sept. 19 | Cloudy | 30° /17° | 3.1 mm | 6 | |
| Sept. 20 | Overcast | 31° /18° | 1.2 mm | 6.9 | |
| Sept. 21 | Overcast | 21° /15° | 3.6 mm | 2.2 | |
| Sept. 22 | Overcast | 17° /14° | 0.1 mm | 3 | |
| Sept. 23 | Overcast | 21° /12° | 0.1 mm | 5.9 | |
| Sept. 24 | Sunny | 22° /12° | 0 mm | 6 | |
| Sept. 25 | Patchy rain possible | 20° /15° | 1.2 mm | 5 | |
| Sept. 26 | Partly cloudy | 23° /14° | 0 mm | 6 | |
| Sept. 27 | Sunny | 25° /14° | 0 mm | 6 | |
| Sept. 28 | Overcast | 17° /10° | 5.4 mm | 4 | |
| Sept. 29 | Sunny | 16° /6° | 0 mm | 5 | |
| Sept. 30 | Sunny | 23° /11° | 0 mm | 6 | |
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Important Notice
Our weather forecast for Decatur 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 Decatur forecast closer to your planned date for the most up-to-date weather information.
Change Month
Decatur in September - FAQ
What are the expected maximum and minimum temperatures in Decatur during September?
Enjoy moderate daytime temperatures of up to 27° and cooler nights around 14°. Ideal for a range of outdoor activities, from hiking to city tours.
How much rainfall should be expected in Decatur during September?
Significant rainfall exceeding 198.9 mm is expected in Decatur during September, occurring over more than 7 days. Preparing for wet conditions is recommended in your planning.
What are the typical wind conditions in Decatur during September?
The average wind speed in Decatur during September is 17 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in Decatur
Explore the daily rainfall trends and prepare for Decaturs September weather 💧
Typically, Decatur has 7 rainy days in September with a total of 198.9 mm of rainfall.
UV exposure in Decatur during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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