Weather in Winnebago County, Illinois for September 2026
Flood Watch - See hour by hour.
So far, September 2026 in Winnebago County is slightly warmer than the historical average by 1.5 °F.
Expect cooler weather in the next days in Winnebago County with the forecast suggesting a temperature of 17.1 °F, lower than the historical average.
In general, the average temperature in Winnebago County at the beginning of September is 28.1 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 19 °F by the end of September.
The climate of Winnebago County in September is notably wet, with an average of 11 rainy days, and a total of 72.2 mm of precipitation.
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Winnebago County Weather September
Temperatures trend during September in Winnebago County
September weather in Winnebago County day by day
| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Sunny | 29° /12° | 0 mm | 7 | |
| Sept. 2 | Sunny | 30° /13° | 0 mm | 7 | |
| Sept. 3 |  Partly cloudy | 31° /14° | 8.6 mm | 7 | |
| Sept. 4 |  Cloudy | 30° /14° | 0 mm | 6 | |
| Sept. 5 |  Overcast | 29° /16° | 0.8 mm | 6 | |
| Sept. 6 |  Patchy rain possible | 25° /11° | 1 mm | 5 | |
| Sept. 7 | Patchy rain possible | 23° /8° | 0.1 mm | 5 | |
| Sept. 8 |  Mist | 25° /9° | 0 mm | 5 | |
| Sept. 9 | Mist | 27° /11° | 16.9 mm | 5 | |
| Sept. 10 | Fog | 28° /12° | 0 mm | 6 | |
| Sept. 11 | Light rain shower | 26° /13° | 3.5 mm | 6 | |
| Sept. 12 | Fog | 27° /13° | 0 mm | 6 | |
| Sept. 13 | Mist | 26° /14° | 0.6 mm | 6 | |
| Sept. 14 | Mist | 27° /11° | 0 mm | 6 | |
| Sept. 15 | Mist | 29° /14° | 5.8 mm | 6 | |
| Sept. 16 | Light rain shower | 28° /14° | 1.3 mm | 5 | |
| Sept. 17 | Sunny | 26° /12° | 9.8 mm | 5 | |
| Sept. 18 | Mist | 26° /11° | 0.6 mm | 6 | |
| Sept. 19 |  Moderate or heavy rain with thunder | 26° /13° | 26.5 mm | 5 | |
| Sept. 20 | Light rain shower | 20° /14° | 57.9 mm | 0.7 | |
| Sept. 21 | Overcast | 15° /12° | 0.6 mm | 1 | |
| Sept. 22 | Patchy rain possible | 16° /10° | 0.7 mm | 5.3 | |
| Sept. 23 | Sunny | 18° /10° | 0.2 mm | 5.2 | |
| Sept. 24 | Overcast | 19° /11° | 0 mm | 5.1 | |
| Sept. 25 | Overcast | 18° /13° | 0 mm | 4 | |
| Sept. 26 | Overcast | 15° /14° | 0 mm | 3 | |
| Sept. 27 | Sunny | 21° /14° | 0 mm | 6 | |
| Sept. 28 | Sunny | 21° /13° | 0 mm | 6 | |
| Sept. 29 | Overcast | 21° /12° | 0 mm | 5 | |
| Sept. 30 | Patchy rain possible | 18° /11° | 4 mm | 4 | |
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Winnebago County in September - FAQ
What are the expected maximum and minimum temperatures in Winnebago County during September?
How much rainfall should be expected in Winnebago County during September?
What are the typical wind conditions in Winnebago County during September?
September rainfall patterns in Winnebago County
UV exposure in Winnebago County during September
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Where is Winnebago County?Get accurate weather forecasts for Winnebago County, located at latitude 42.271 and longitude -89.094. Stay updated with localized weather information tailored for Winnebago County.