September is one of the warmer months of the year in Stillwater, with average highs near 30.3°C and lows around 17.5°C (mean 23.9°C). It is about average for rainfall, averaging 90 mm of rainfall and 61% relative humidity across the period.
September is one of the warmer months of the year in Stillwater. Across 45 years of records, the warmest September in Stillwater was 1998 — when the month averaged 28.5°C — while the coldest was 1989 at 19.9°C. Typical September days reach 30.3°C with nights near 17.5°C. The long-term trend is warming, about 0.6°C per decade.
September is about average for rainfall in Stillwater, averaging 90 mm of rainfall. The wettest September on record was 1986 with 259 mm, while the driest was 2000 at 20 mm.
Relative humidity in Stillwater during September averages 61%. The most humid September was 2007 at 80%, and the least humid was 2000 at 39%.
September receives about 5.1 kWh/m²/day of solar energy in Stillwater. The sunniest Septembers were 2000 and 2004 at 5.7 kWh/m²/day, and the cloudiest were 1986 and 2018 at 4.3.
Average wind speed in Stillwater during September is 2.9 m/s. The windiest Septembers were 1984 and 1986 at 3.7 m/s, while the calmest was 2025 at 2.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 23.4°C | 23.0°C | 23.4°C | 24.8°C | 25.5°C | +2.1°C |
| Avg High | 29.7°C | 29.2°C | 29.8°C | 31.0°C | 32.5°C | +2.8°C |
| Avg Low | 17.1°C | 16.8°C | 17.0°C | 18.6°C | 18.6°C | +1.5°C |
| Avg Rain | 111 mm | 125 mm | 75 mm | 80 mm | 40 mm | -71 mm |
September temperatures in Stillwater have risen by about 2.2°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 2°C (1985) to a record high of 43.9°C (2000).
Rainfall in September is about average for rainfall, averaging 90 mm, with a wettest year of 259 mm.
One of the best times to visit Stillwater
September is one of the best times to visit Stillwater. Expect days averaging 30.3°C and nights around 17.5°C (mean 23.9°C) — warmer than Stillwater's yearly average — with higher rainfall (90 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 | 31.3°C | 24.8°C | 18.4°C | 35.5°C | 13.2°C | 23 mm | 62% | 2.1 m/s | 5 |
| 2024 | 33.0°C | 25.7°C | 18.3°C | 39.4°C | 13.1°C | 25 mm | 51% | 2.4 m/s | 5.6 |
| 2023 | 34.1°C | 26.9°C | 19.7°C | 39.7°C | 15.9°C | 52 mm | 54% | 2.9 m/s | 5.2 |
| 2022 | 33.8°C | 26.3°C | 18.9°C | 38.9°C | 13.6°C | 22 mm | 48% | 2.8 m/s | 5.6 |
| 2021 | 34.3°C | 27.1°C | 19.8°C | 39.0°C | 11.9°C | 30 mm | 50% | 3.1 m/s | 5.6 |
| 2020 | 28.4°C | 22.3°C | 16.3°C | 35.0°C | 8.0°C | 86 mm | 71% | 2.7 m/s | 4.8 |
| 2019 | 31.4°C | 26.3°C | 21.2°C | 34.7°C | 17.3°C | 128 mm | 76% | 2.9 m/s | 5.3 |
| 2018 | 29.0°C | 24.0°C | 19.0°C | 36.0°C | 9.0°C | 115 mm | 75% | 2.7 m/s | 4.3 |
| 2017 | 30.4°C | 24.2°C | 18.0°C | 35.8°C | 11.8°C | 73 mm | 62% | 2.8 m/s | 4.9 |
| 2016 | 31.3°C | 25.2°C | 19.1°C | 36.9°C | 10.2°C | 60 mm | 65% | 3 m/s | 5.2 |
| 2015 | 31.4°C | 25.2°C | 19.0°C | 38.6°C | 12.6°C | 81 mm | 65% | 3 m/s | 5.2 |
| 2014 | 30.5°C | 24.2°C | 18.0°C | 37.2°C | 9.1°C | 76 mm | 64% | 3.1 m/s | 5.1 |
| 2013 | 32.3°C | 25.4°C | 18.5°C | 38.6°C | 8.9°C | 65 mm | 56% | 2.8 m/s | 5.3 |
| 2012 | 32.2°C | 25.2°C | 18.2°C | 41.9°C | 12.3°C | 52 mm | 52% | 2.8 m/s | 5 |
| 2011 | 30.3°C | 23.1°C | 15.9°C | 41.6°C | 10.4°C | 69 mm | 46% | 3 m/s | 5.5 |
| 2010 | 31.2°C | 25.0°C | 18.9°C | 37.5°C | 8.2°C | 83 mm | 65% | 3.3 m/s | 5.3 |
| 2009 | 27.1°C | 21.6°C | 16.0°C | 34.2°C | 8.8°C | 92 mm | 73% | 2.7 m/s | 4.4 |
| 2008 | 28.2°C | 22.2°C | 16.1°C | 33.5°C | 9.5°C | 90 mm | 70% | 2.6 m/s | 4.8 |
| 2007 | 27.7°C | 22.7°C | 17.6°C | 31.2°C | 11.9°C | 114 mm | 80% | 2.7 m/s | 4.9 |
| 2006 | 29.4°C | 22.4°C | 15.3°C | 35.1°C | 10.0°C | 51 mm | 53% | 2.9 m/s | 5.3 |
| 2005 | 32.4°C | 25.8°C | 19.2°C | 36.0°C | 9.5°C | 77 mm | 61% | 2.9 m/s | 5.5 |
| 2004 | 31.9°C | 24.8°C | 17.7°C | 36.5°C | 12.0°C | 26 mm | 53% | 3 m/s | 5.7 |
| 2003 | 27.0°C | 21.1°C | 15.2°C | 32.5°C | 8.4°C | 92 mm | 68% | 3 m/s | 4.8 |
| 2002 | 31.5°C | 24.6°C | 17.8°C | 38.0°C | 10.3°C | 87 mm | 57% | 2.6 m/s | 5.5 |
| 2001 | 29.1°C | 22.8°C | 16.4°C | 35.7°C | 6.9°C | 101 mm | 62% | 2.5 m/s | 5.3 |
| 2000 | 34.0°C | 26.1°C | 18.3°C | 43.9°C | 5.2°C | 20 mm | 39% | 3.3 m/s | 5.7 |
| 1999 | 28.1°C | 21.8°C | 15.5°C | 37.4°C | 7.5°C | 149 mm | 62% | 3 m/s | 4.6 |
| 1998 🔥 | 35.0°C | 28.5°C | 21.9°C | 43.8°C | 16.7°C | 106 mm | 55% | 3 m/s | 5.3 |
| 1997 | 31.1°C | 24.5°C | 18.0°C | 37.8°C | 12.1°C | 87 mm | 61% | 3 m/s | 4.9 |
| 1996 | 28.1°C | 21.8°C | 15.5°C | 35.7°C | 5.3°C | 153 mm | 66% | 2.6 m/s | 4.5 |
| 1995 | 27.4°C | 21.7°C | 15.9°C | 39.3°C | 2.5°C | 140 mm | 69% | 2.8 m/s | 4.4 |
| 1994 | 28.9°C | 22.4°C | 15.9°C | 35.0°C | 6.7°C | 65 mm | 63% | 2.8 m/s | 5.1 |
| 1993 | 27.2°C | 20.7°C | 14.3°C | 31.8°C | 5.9°C | 166 mm | 70% | 3 m/s | 4.9 |
| 1992 | 27.8°C | 21.7°C | 15.6°C | 31.8°C | 6.7°C | 104 mm | 73% | 3.1 m/s | 5.3 |
| 1991 | 27.0°C | 21.6°C | 16.3°C | 34.3°C | 6.7°C | 143 mm | 70% | 2.8 m/s | 4.6 |
| 1990 | 31.8°C | 25.5°C | 19.1°C | 40.1°C | 8.2°C | 135 mm | 60% | 2.3 m/s | 4.9 |
| 1989 ❄️ | 25.8°C | 19.9°C | 13.9°C | 34.1°C | 2.1°C | 123 mm | 69% | 2.8 m/s | 4.9 |
| 1988 | 30.7°C | 23.6°C | 16.6°C | 38.1°C | 10.7°C | 158 mm | 59% | 2.7 m/s | 5 |
| 1987 | 28.6°C | 22.3°C | 15.9°C | 34.7°C | 8.6°C | 132 mm | 67% | 2.3 m/s | 5.2 |
| 1986 🌧️ | 29.6°C | 24.7°C | 19.8°C | 33.8°C | 11.3°C | 259 mm | 72% | 3.7 m/s | 4.3 |
| 1985 | 29.5°C | 23.6°C | 17.6°C | 40.6°C | 2.0°C | 135 mm | 61% | 3.6 m/s | 4.7 |
| 1984 | 29.8°C | 23.2°C | 16.6°C | 38.8°C | 3.5°C | 46 mm | 50% | 3.7 m/s | 4.8 |
| 1983 | 31.8°C | 24.9°C | 18.1°C | 39.4°C | 4.5°C | 62 mm | 52% | 3.6 m/s | — |
| 1982 | 31.2°C | 24.4°C | 17.7°C | 37.9°C | 7.6°C | 37 mm | 53% | 3.3 m/s | — |
| 1981 | 30.6°C | 24.0°C | 17.4°C | 36.0°C | 7.7°C | 44 mm | 58% | 3 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 30.3°C with lows near 17.5°C (mean 23.9°C), based on 45 years of NASA POWER data.
September averages 90 mm of rainfall in Stillwater, about average for rainfall. The wettest on record was 259 mm in 1986.
The hottest September reached 43.9°C in 2000. The coldest dipped to 2°C in 1985.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2.2°C. Daytime highs moved from 30.6°C to 33.3°C and overnight lows from 17.5°C to 19°C over the same span.
September is one of the warmer months of the year in Stillwater and about average for rainfall, so plan for around 30.3°C daytime highs and 17.5°C at night.
Not quite — September is the 9th coolest month in Stillwater, averaging 23.9°C.
For September in Stillwater, pack light, breathable clothing and sun protection, with typical highs of 30.3°C and lows of 17.5°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 61% — moderately humid.
Average wind speed in September is 2.9 m/s. The windiest September on record averaged 3.7 m/s (1984).
The wettest September on record was 1986 with 259 mm. On average, September sees 90 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 Stillwater 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.
