Weather in Allegheny County, Pennsylvania for September 2025
Until now, September 2025 in Allegheny County is cooler than usual, with temperatures averaging 23.4 °F, this is -3 °F below the typical seasonal average.
The forecast for the next days in Allegheny County predicts temperatures to be around 27 °F, close to the historical average.
In general, the average temperature in Allegheny County at the beginning of September is 26.9 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 22.6 °F by the end of September.
The climate of Allegheny County in September is notably wet, with an average of 14 rainy days, and a total of 94 mm of precipitation.
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Allegheny County Weather September
Temperatures trend during September in Allegheny County
September weather in Allegheny County day by day
| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Sunny | 27° /13° | 0 mm | 6 | |
| Sept. 2 |  Mist | 26° /12° | 0 mm | 6 | |
| Sept. 3 |  Overcast | 27° /13° | 0 mm | 6 | |
| Sept. 4 |  Thundery outbreaks possible | 27° /15° | 20.7 mm | 6 | |
| Sept. 5 |  Partly cloudy | 30° /15° | 0 mm | 7 | |
| Sept. 6 | Thundery outbreaks possible | 28° /16° | 21.8 mm | 7 | |
| Sept. 7 |  Light rain shower | 23° /13° | 4 mm | 5 | |
| Sept. 8 | Overcast | 23° /10° | 0 mm | 6 | |
| Sept. 9 | Partly cloudy | 25° /11° | 0.8 mm | 6 | |
| Sept. 10 | Sunny | 27° /12° | 5.3 mm | 7 | |
| Sept. 11 | Mist | 27° /13° | 0 mm | 6 | |
| Sept. 12 | Mist | 28° /14° | 0 mm | 7 | |
| Sept. 13 | Overcast | 25° /14° | 1.9 mm | 6 | |
| Sept. 14 | Mist | 27° /14° | 0 mm | 7 | |
| Sept. 15 | Partly cloudy | 31° /16° | 0 mm | 1.4 | |
| Sept. 16 | Partly cloudy | 27° /17° | 0 mm | 1.5 | |
| Sept. 17 | Partly cloudy | 25° /18° | 0 mm | 1.5 | |
| Sept. 18 |  Cloudy | 30° /18° | 0 mm | 1.5 | |
| Sept. 19 | Sunny | 32° /16° | 0 mm | 0 | |
| Sept. 20 | Sunny | 31° /18° | 0 mm | 6 | |
| Sept. 21 | Partly cloudy | 29° /17° | 0 mm | 6 | |
| Sept. 22 | Sunny | 30° /16° | 0 mm | 6 | |
| Sept. 23 | Sunny | 31° /18° | 0 mm | 6 | |
| Sept. 24 | Patchy rain possible | 24° /15° | 4.9 mm | 4 | |
| Sept. 25 | Partly cloudy | 22° /13° | 0.1 mm | 5 | |
| Sept. 26 | Patchy rain possible | 23° /13° | 0.4 mm | 4 | |
| Sept. 27 | Patchy rain possible | 21° /14° | 0.3 mm | 4 | |
| Sept. 28 | Partly cloudy | 24° /13° | 0 mm | 5 | |
| Sept. 29 | Light rain shower | 24° /16° | 1.4 mm | 5 | |
| Sept. 30 | Mist | 20° /13° | 24.3 mm | 5 | |
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Allegheny County in September - FAQ
September rainfall patterns in Allegheny County
UV exposure in Allegheny County during September
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Where is Allegheny County?Get accurate weather forecasts for Allegheny County, located at latitude 40.441 and longitude -79.996. Stay updated with localized weather information tailored for Allegheny County.