September is one of the warmer months of the year in Johnstown, with average highs near 23.5°C and lows around 11.2°C (mean 17.4°C). It is about average for rainfall, averaging 93 mm of rainfall and 72% relative humidity across the period.
September is one of the warmer months of the year in Johnstown. Across 45 years of records, the warmest September in Johnstown was 2016 — when the month averaged 20.1°C — while the coldest was 1984 at 14.9°C. Typical September days reach 23.5°C with nights near 11.2°C. The long-term trend is warming, about 0.5°C per decade.
September is about average for rainfall in Johnstown, averaging 93 mm of rainfall. The wettest September on record was 2018 with 240 mm, while the driest was 2014 at 29 mm.
Relative humidity in Johnstown during September averages 72%. The most humid September was 2018 at 87%, and the least humid was 2005 at 61%.
September receives about 4.1 kWh/m²/day of solar energy in Johnstown. 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 Johnstown 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 2018 at 0 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 16.6°C | 16.6°C | 17.3°C | 18.3°C | 18.0°C | +1.4°C |
| Avg High | 22.9°C | 22.9°C | 23.4°C | 24.4°C | 24.0°C | +1.1°C |
| Avg Low | 10.4°C | 10.4°C | 11.2°C | 12.2°C | 12.0°C | +1.6°C |
| Avg Rain | 78 mm | 95 mm | 96 mm | 105 mm | 87 mm | +9 mm |
September temperatures in Johnstown have risen by about 1.4°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -0.7°C (2000) to a record high of 33.6°C (2015).
Rainfall in September is about average for rainfall, averaging 93 mm, with a wettest year of 240 mm.
One of the best times to visit Johnstown
September is one of the best times to visit Johnstown. Expect days averaging 23.5°C and nights around 11.2°C (mean 17.4°C) — warmer than Johnstown's yearly average — with higher rainfall (93 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 | 25.9°C | 19.2°C | 12.4°C | 29.6°C | 7.0°C | 57 mm | 64% | 0.1 m/s | 4.4 |
| 2024 | 24.1°C | 18.2°C | 12.3°C | 29.0°C | 6.1°C | 74 mm | 74% | 0.1 m/s | 4.3 |
| 2023 | 23.8°C | 17.9°C | 12.0°C | 33.4°C | 5.9°C | 76 mm | 74% | 0.1 m/s | 4.3 |
| 2022 | 22.4°C | 17.1°C | 11.8°C | 30.9°C | 2.9°C | 112 mm | 79% | 0.1 m/s | 4 |
| 2021 | 23.0°C | 17.5°C | 11.9°C | 28.1°C | 5.8°C | 155 mm | 80% | 0.1 m/s | 4.3 |
| 2020 | 24.5°C | 17.9°C | 11.3°C | 31.6°C | 2.0°C | 49 mm | 67% | 0.1 m/s | 4.1 |
| 2019 | 26.3°C | 19.8°C | 13.3°C | 30.8°C | 7.9°C | 41 mm | 71% | 0.1 m/s | 4.3 |
| 2018 🌧️ | 23.7°C | 19.3°C | 14.8°C | 31.8°C | 6.5°C | 240 mm | 87% | 0 m/s | 3.3 |
| 2017 | 24.5°C | 18.1°C | 11.7°C | 31.6°C | 4.8°C | 36 mm | 70% | 0.1 m/s | 4.3 |
| 2016 🔥 | 26.7°C | 20.1°C | 13.5°C | 32.4°C | 6.7°C | 76 mm | 66% | 0.1 m/s | 4.6 |
| 2015 | 25.9°C | 19.6°C | 13.2°C | 33.6°C | 6.6°C | 94 mm | 68% | 0.1 m/s | 4.3 |
| 2014 | 24.2°C | 17.6°C | 10.9°C | 31.6°C | 3.8°C | 29 mm | 70% | 0.1 m/s | 4.4 |
| 2013 | 23.5°C | 16.5°C | 9.5°C | 31.6°C | 2.3°C | 50 mm | 69% | 0.1 m/s | 4.5 |
| 2012 | 23.3°C | 17.1°C | 11.0°C | 31.8°C | 4.0°C | 115 mm | 72% | 0.1 m/s | 4 |
| 2011 | 21.7°C | 17.2°C | 12.8°C | 32.7°C | 2.4°C | 236 mm | 86% | 0.1 m/s | 3.3 |
| 2010 | 24.6°C | 18.1°C | 11.6°C | 33.4°C | 7.0°C | 133 mm | 63% | 0.1 m/s | 4.4 |
| 2009 | 22.3°C | 16.8°C | 11.3°C | 28.0°C | 6.1°C | 65 mm | 73% | 0.1 m/s | 3.9 |
| 2008 | 23.8°C | 17.8°C | 11.8°C | 31.4°C | 6.2°C | 95 mm | 73% | 0.1 m/s | 4.2 |
| 2007 | 25.2°C | 18.3°C | 11.3°C | 31.7°C | 2.9°C | 42 mm | 70% | 0.1 m/s | 5.1 |
| 2006 | 19.9°C | 15.1°C | 10.3°C | 26.0°C | 3.4°C | 114 mm | 82% | 0.1 m/s | 3.5 |
| 2005 | 27.0°C | 19.7°C | 12.5°C | 32.0°C | 4.3°C | 31 mm | 61% | 0.1 m/s | 4.7 |
| 2004 | 22.7°C | 17.5°C | 12.2°C | 27.0°C | 4.0°C | 231 mm | 82% | 0.1 m/s | 4.2 |
| 2003 | 21.2°C | 16.1°C | 11.1°C | 25.6°C | 4.6°C | 157 mm | 83% | 0.1 m/s | 3.5 |
| 2002 | 26.1°C | 19.3°C | 12.4°C | 33.4°C | 6.8°C | 88 mm | 62% | 0.1 m/s | 4.5 |
| 2001 | 23.5°C | 16.4°C | 9.3°C | 32.1°C | 3.0°C | 57 mm | 62% | 0.1 m/s | 4.7 |
| 2000 | 22.7°C | 16.2°C | 9.6°C | 30.5°C | -0.7°C | 81 mm | 70% | 0.1 m/s | 4.1 |
| 1999 | 24.2°C | 17.5°C | 10.8°C | 31.7°C | 1.6°C | 107 mm | 67% | 0.1 m/s | 4.2 |
| 1998 | 25.9°C | 19.0°C | 12.0°C | 33.0°C | 3.9°C | 54 mm | 64% | 0.1 m/s | 4.6 |
| 1997 | 22.2°C | 16.0°C | 9.8°C | 28.6°C | 3.4°C | 94 mm | 71% | 0.1 m/s | 4.2 |
| 1996 | 20.6°C | 16.0°C | 11.4°C | 29.4°C | 5.3°C | 223 mm | 84% | 0.1 m/s | 3.6 |
| 1995 | 23.5°C | 16.5°C | 9.6°C | 30.6°C | 0.8°C | 41 mm | 62% | 0.1 m/s | 4.2 |
| 1994 | 21.3°C | 15.4°C | 9.5°C | 27.3°C | 5.1°C | 57 mm | 76% | 0.1 m/s | 4.2 |
| 1993 | 22.5°C | 16.6°C | 10.8°C | 31.6°C | 2.2°C | 122 mm | 73% | 0.1 m/s | 3.3 |
| 1992 | 22.6°C | 16.3°C | 10.0°C | 28.4°C | 0.7°C | 83 mm | 75% | 0.1 m/s | 3.9 |
| 1991 | 23.9°C | 16.9°C | 10.0°C | 32.6°C | 2.1°C | 63 mm | 62% | 0.1 m/s | 4.2 |
| 1990 | 21.8°C | 16.1°C | 10.4°C | 28.5°C | 0.5°C | 110 mm | 79% | 0.1 m/s | 3.8 |
| 1989 | 22.3°C | 16.6°C | 10.8°C | 29.2°C | 0.3°C | 91 mm | 79% | 0.1 m/s | 3.5 |
| 1988 | 22.2°C | 15.7°C | 9.2°C | 27.0°C | 3.8°C | 103 mm | 74% | 0.1 m/s | 4.1 |
| 1987 | 21.6°C | 16.5°C | 11.5°C | 26.3°C | 2.9°C | 134 mm | 81% | 0.1 m/s | 3.7 |
| 1986 | 24.2°C | 18.1°C | 12.0°C | 29.7°C | 1.9°C | 82 mm | 71% | 0.1 m/s | 4.1 |
| 1985 | 25.1°C | 18.0°C | 10.9°C | 31.3°C | 3.1°C | 36 mm | 62% | 0.1 m/s | 4.7 |
| 1984 ❄️ | 21.4°C | 14.9°C | 8.3°C | 28.9°C | 1.4°C | 41 mm | 73% | 0.1 m/s | 4.4 |
| 1983 | 24.7°C | 17.5°C | 10.3°C | 32.1°C | 1.2°C | 63 mm | 62% | 0.1 m/s | — |
| 1982 | 23.2°C | 16.8°C | 10.4°C | 30.2°C | 4.3°C | 67 mm | 70% | 0.1 m/s | — |
| 1981 | 21.2°C | 15.6°C | 10.0°C | 27.1°C | 2.2°C | 89 mm | 76% | 0.1 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 23.5°C with lows near 11.2°C (mean 17.4°C), based on 45 years of NASA POWER data.
September averages 93 mm of rainfall in Johnstown, about average for rainfall. The wettest on record was 240 mm in 2018.
The hottest September reached 33.6°C in 2015. The coldest dipped to -0.7°C in 2000.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.4°C. Daytime highs moved from 23.1°C to 23.8°C and overnight lows from 10°C to 12.1°C over the same span.
September is one of the warmer months of the year in Johnstown and about average for rainfall, so plan for around 23.5°C daytime highs and 11.2°C at night.
Not quite — September is the 9th coolest month in Johnstown, averaging 17.4°C.
For September in Johnstown, pack light layers you can adjust through the day, with typical highs of 23.5°C and lows of 11.2°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 72% — moderately humid.
Average wind speed in September is 0.1 m/s. The windiest September on record averaged 0.1 m/s (1981).
The wettest September on record was 2018 with 240 mm. On average, September sees 93 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 Johnstown 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.
