September is one of the warmer months of the year in Altoona, with average highs near 24.6°C and lows around 11.7°C (mean 18.2°C). It is about average for rainfall, averaging 96 mm of rainfall and 71% relative humidity across the period.
September is one of the warmer months of the year in Altoona. Across 45 years of records, the warmest September in Altoona was 2016 — when the month averaged 20.8°C — while the coldest was 2006 at 15.9°C. Typical September days reach 24.6°C with nights near 11.7°C. The long-term trend is warming, about 0.5°C per decade.
September is about average for rainfall in Altoona, averaging 96 mm of rainfall. The wettest September on record was 2011 with 264 mm, while the driest was 2005 at 27 mm.
Relative humidity in Altoona during September averages 71%. The most humid September was 2018 at 88%, and the least humid was 1983 at 59%.
September receives about 4.1 kWh/m²/day of solar energy in Altoona. The sunniest September was 2007 at 5.1 kWh/m²/day, and the cloudiest were 1993, 2011 and 2018 at 3.3.
Average wind speed in Altoona during September is 0.1 m/s. The windiest Septembers were 2023, 2024 and 2025, among others at 0.1 m/s, while the calmest was 1981 at 0 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 17.5°C | 17.5°C | 18.0°C | 19.1°C | 18.7°C | +1.2°C |
| Avg High | 24.2°C | 23.9°C | 24.3°C | 25.5°C | 24.9°C | +0.7°C |
| Avg Low | 10.9°C | 11.0°C | 11.6°C | 12.7°C | 12.5°C | +1.6°C |
| Avg Rain | 74 mm | 100 mm | 99 mm | 109 mm | 95 mm | +21 mm |
September temperatures in Altoona have risen by about 1.2°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -0.1°C (2000) to a record high of 35.3°C (2023).
Rainfall in September is about average for rainfall, averaging 96 mm, with a wettest year of 264 mm.
One of the best times to visit Altoona
September is one of the best times to visit Altoona. Expect days averaging 24.6°C and nights around 11.7°C (mean 18.2°C) — warmer than Altoona's yearly average — with higher rainfall (96 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 27.3°C | 20.2°C | 13.1°C | 31.3°C | 7.3°C | 47 mm | 62% | 0.1 m/s | 4.4 |
| 2024 | 25.0°C | 19.0°C | 13.1°C | 30.6°C | 7.3°C | 66 mm | 73% | 0.1 m/s | 4.3 |
| 2023 | 24.7°C | 18.6°C | 12.5°C | 35.3°C | 6.8°C | 89 mm | 74% | 0.1 m/s | 4.3 |
| 2022 | 23.7°C | 18.1°C | 12.4°C | 30.4°C | 4.0°C | 98 mm | 76% | 0.1 m/s | 4 |
| 2021 | 23.6°C | 18.0°C | 12.3°C | 28.4°C | 7.1°C | 208 mm | 82% | 0.1 m/s | 4.3 |
| 2020 | 25.3°C | 18.4°C | 11.5°C | 31.9°C | 2.7°C | 61 mm | 67% | 0.1 m/s | 4.1 |
| 2019 | 27.6°C | 20.6°C | 13.6°C | 33.0°C | 7.4°C | 34 mm | 68% | 0.1 m/s | 4.3 |
| 2018 | 24.3°C | 19.7°C | 15.1°C | 32.4°C | 6.4°C | 256 mm | 88% | 0.1 m/s | 3.3 |
| 2017 | 25.4°C | 18.8°C | 12.2°C | 33.1°C | 5.4°C | 38 mm | 69% | 0.1 m/s | 4.3 |
| 2016 🔥 | 27.7°C | 20.8°C | 13.9°C | 34.0°C | 6.7°C | 80 mm | 64% | 0.1 m/s | 4.6 |
| 2015 | 26.8°C | 20.2°C | 13.7°C | 34.5°C | 7.6°C | 83 mm | 67% | 0.1 m/s | 4.3 |
| 2014 | 25.3°C | 18.3°C | 11.3°C | 33.5°C | 4.4°C | 32 mm | 68% | 0.1 m/s | 4.4 |
| 2013 | 24.8°C | 17.5°C | 10.2°C | 34.0°C | 2.4°C | 44 mm | 65% | 0.1 m/s | 4.5 |
| 2012 | 24.4°C | 18.0°C | 11.7°C | 33.5°C | 3.7°C | 115 mm | 71% | 0.1 m/s | 4 |
| 2011 🌧️ | 22.9°C | 18.1°C | 13.4°C | 34.5°C | 3.5°C | 264 mm | 86% | 0.1 m/s | 3.3 |
| 2010 | 26.1°C | 19.2°C | 12.3°C | 35.2°C | 6.3°C | 144 mm | 61% | 0.1 m/s | 4.4 |
| 2009 | 23.2°C | 17.5°C | 11.7°C | 29.5°C | 6.1°C | 64 mm | 71% | 0.1 m/s | 3.9 |
| 2008 | 24.6°C | 18.3°C | 12.0°C | 32.6°C | 6.2°C | 102 mm | 73% | 0.1 m/s | 4.2 |
| 2007 | 26.2°C | 19.1°C | 11.9°C | 33.3°C | 3.5°C | 40 mm | 68% | 0.1 m/s | 5.1 |
| 2006 ❄️ | 21.0°C | 15.9°C | 10.8°C | 26.9°C | 3.4°C | 111 mm | 81% | 0.1 m/s | 3.5 |
| 2005 | 27.8°C | 20.4°C | 13.1°C | 32.9°C | 4.3°C | 27 mm | 60% | 0.1 m/s | 4.7 |
| 2004 | 23.7°C | 18.1°C | 12.6°C | 28.8°C | 4.5°C | 261 mm | 81% | 0.1 m/s | 4.2 |
| 2003 | 22.2°C | 16.8°C | 11.4°C | 27.4°C | 4.2°C | 167 mm | 83% | 0.1 m/s | 3.5 |
| 2002 | 26.9°C | 19.9°C | 12.9°C | 35.2°C | 7.0°C | 88 mm | 62% | 0.1 m/s | 4.5 |
| 2001 | 24.5°C | 17.1°C | 9.7°C | 31.6°C | 3.1°C | 58 mm | 61% | 0.1 m/s | 4.7 |
| 2000 | 23.4°C | 16.8°C | 10.1°C | 31.3°C | -0.1°C | 71 mm | 69% | 0.1 m/s | 4.1 |
| 1999 | 24.6°C | 18.1°C | 11.5°C | 32.0°C | 3.9°C | 127 mm | 69% | 0.1 m/s | 4.2 |
| 1998 | 27.2°C | 19.9°C | 12.5°C | 33.6°C | 3.8°C | 52 mm | 62% | 0.1 m/s | 4.6 |
| 1997 | 23.3°C | 16.9°C | 10.5°C | 30.3°C | 3.0°C | 102 mm | 69% | 0.1 m/s | 4.2 |
| 1996 | 21.8°C | 16.7°C | 11.7°C | 30.2°C | 5.5°C | 245 mm | 83% | 0.1 m/s | 3.6 |
| 1995 | 24.7°C | 17.5°C | 10.3°C | 31.4°C | 2.0°C | 41 mm | 60% | 0.1 m/s | 4.2 |
| 1994 | 22.4°C | 16.4°C | 10.4°C | 28.9°C | 5.5°C | 65 mm | 74% | 0.1 m/s | 4.2 |
| 1993 | 23.8°C | 17.7°C | 11.6°C | 32.4°C | 3.0°C | 124 mm | 71% | 0.1 m/s | 3.3 |
| 1992 | 23.5°C | 17.0°C | 10.5°C | 30.3°C | 1.0°C | 86 mm | 74% | 0.1 m/s | 3.9 |
| 1991 | 24.9°C | 17.7°C | 10.5°C | 34.4°C | 1.3°C | 66 mm | 61% | 0.1 m/s | 4.2 |
| 1990 | 23.1°C | 16.9°C | 10.7°C | 30.0°C | 1.4°C | 95 mm | 76% | 0.1 m/s | 3.8 |
| 1989 | 24.0°C | 17.7°C | 11.5°C | 32.1°C | 1.8°C | 81 mm | 74% | 0.1 m/s | 3.5 |
| 1988 | 23.1°C | 16.3°C | 9.6°C | 27.7°C | 4.2°C | 99 mm | 73% | 0.1 m/s | 4.1 |
| 1987 | 22.7°C | 17.2°C | 11.7°C | 27.7°C | 3.4°C | 128 mm | 80% | 0.1 m/s | 3.7 |
| 1986 | 25.1°C | 18.6°C | 12.0°C | 31.6°C | 2.9°C | 77 mm | 70% | 0.1 m/s | 4.1 |
| 1985 | 26.2°C | 18.9°C | 11.6°C | 33.4°C | 4.3°C | 43 mm | 62% | 0.1 m/s | 4.7 |
| 1984 | 23.1°C | 16.0°C | 8.9°C | 29.9°C | 2.7°C | 38 mm | 69% | 0.1 m/s | 4.4 |
| 1983 | 26.1°C | 18.6°C | 11.2°C | 33.6°C | 2.4°C | 56 mm | 59% | 0.1 m/s | — |
| 1982 | 24.5°C | 17.7°C | 11.0°C | 30.5°C | 5.0°C | 63 mm | 69% | 0.1 m/s | — |
| 1981 | 22.8°C | 16.6°C | 10.4°C | 29.4°C | 3.0°C | 79 mm | 73% | 0 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 24.6°C with lows near 11.7°C (mean 18.2°C), based on 45 years of NASA POWER data.
September averages 96 mm of rainfall in Altoona, about average for rainfall. The wettest on record was 264 mm in 2011.
The hottest September reached 35.3°C in 2023. The coldest dipped to -0.1°C in 2000.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.2°C. Daytime highs moved from 24.5°C to 24.9°C and overnight lows from 10.6°C to 12.7°C over the same span.
September is one of the warmer months of the year in Altoona and about average for rainfall, so plan for around 24.6°C daytime highs and 11.7°C at night.
Not quite — September is the 9th coolest month in Altoona, averaging 18.2°C.
For September in Altoona, pack light layers you can adjust through the day, with typical highs of 24.6°C and lows of 11.7°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 71% — moderately humid.
Average wind speed in September is 0.1 m/s. The windiest September on record averaged 0.1 m/s (1982).
The wettest September on record was 2011 with 264 mm. On average, September sees 96 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Altoona behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
