September is one of the warmer months of the year in Bozeman, with average highs near 18.8°C and lows around 3.5°C (mean 11.2°C). It is about average for rainfall, averaging 43 mm of rainfall and 55% relative humidity across the period.
September is one of the warmer months of the year in Bozeman. Across 45 years of records, the warmest Septembers in Bozeman were 2022 and 2025 — when the month averaged 14.5°C — while the coldest was 1985 at 6.6°C. Typical September days reach 18.8°C with nights near 3.5°C. The long-term trend is warming, about 0.8°C per decade.
September is about average for rainfall in Bozeman, averaging 43 mm of rainfall. The wettest September on record was 2019 with 95 mm, while the driest was 1994 at 9 mm.
Relative humidity in Bozeman during September averages 55%. The most humid September was 1986 at 67%, and the least humid was 1994 at 42%.
September receives about 4.6 kWh/m²/day of solar energy in Bozeman. The sunniest Septembers were 2009, 2011 and 2012 at 5.2 kWh/m²/day, and the cloudiest were 1985 and 1986 at 3.8.
Average wind speed in Bozeman during September is 0.5 m/s. The windiest Septembers were 2014, 2020 and 2021, among others at 0.6 m/s, while the calmest were 2023, 2024 and 2025, among others at 0.5 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 9.4°C | 11.0°C | 11.0°C | 11.5°C | 13.5°C | +4.1°C |
| Avg High | 17.0°C | 18.6°C | 18.8°C | 18.9°C | 21.5°C | +4.5°C |
| Avg Low | 1.9°C | 3.3°C | 3.2°C | 4.2°C | 5.6°C | +3.7°C |
| Avg Rain | 51 mm | 34 mm | 37 mm | 53 mm | 39 mm | -12 mm |
September temperatures in Bozeman have risen by about 4.7°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -9.9°C (1985) to a record high of 33.6°C (2022).
Rainfall in September is about average for rainfall, averaging 43 mm, with a wettest year of 95 mm.
One of the best times to visit Bozeman
September is one of the best times to visit Bozeman. Expect days averaging 18.8°C and nights around 3.5°C (mean 11.2°C) — warmer than Bozeman's yearly average — with moderate rainfall (43 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 | 22.4°C | 14.5°C | 6.7°C | 28.8°C | 0.7°C | 35 mm | 52% | 0.5 m/s | 4.8 |
| 2024 | 22.1°C | 14.1°C | 6.1°C | 30.9°C | -1.9°C | 61 mm | 52% | 0.5 m/s | 4.6 |
| 2023 | 19.8°C | 12.6°C | 5.5°C | 27.0°C | -1.0°C | 59 mm | 61% | 0.5 m/s | 4.6 |
| 2022 🔥 | 22.7°C | 14.5°C | 6.3°C | 33.6°C | -1.9°C | 37 mm | 50% | 0.5 m/s | 4.7 |
| 2021 | 21.1°C | 12.7°C | 4.4°C | 29.5°C | -2.9°C | 14 mm | 46% | 0.6 m/s | 5 |
| 2020 | 20.7°C | 12.5°C | 4.3°C | 31.0°C | -5.5°C | 28 mm | 50% | 0.6 m/s | 4.7 |
| 2019 🌧️ | 17.0°C | 10.9°C | 4.7°C | 28.8°C | -5.5°C | 95 mm | 66% | 0.5 m/s | 3.9 |
| 2018 | 18.4°C | 11.0°C | 3.5°C | 26.8°C | -2.5°C | 14 mm | 57% | 0.5 m/s | 4.6 |
| 2017 | 17.2°C | 10.4°C | 3.5°C | 30.0°C | -3.4°C | 92 mm | 61% | 0.5 m/s | 4 |
| 2016 | 17.4°C | 10.4°C | 3.5°C | 28.5°C | -2.7°C | 53 mm | 62% | 0.5 m/s | 3.9 |
| 2015 | 20.4°C | 12.7°C | 5.0°C | 26.7°C | 0.2°C | 51 mm | 54% | 0.5 m/s | 4.8 |
| 2014 | 18.3°C | 10.9°C | 3.5°C | 25.6°C | -6.1°C | 56 mm | 62% | 0.6 m/s | 4.7 |
| 2013 | 18.9°C | 12.3°C | 5.8°C | 29.0°C | -3.8°C | 84 mm | 62% | 0.5 m/s | 3.9 |
| 2012 | 21.2°C | 12.9°C | 4.6°C | 26.6°C | -0.3°C | 12 mm | 46% | 0.6 m/s | 5.2 |
| 2011 | 21.3°C | 12.9°C | 4.5°C | 25.7°C | -1.5°C | 26 mm | 53% | 0.5 m/s | 5.2 |
| 2010 | 18.7°C | 11.0°C | 3.2°C | 24.8°C | -0.9°C | 49 mm | 62% | 0.5 m/s | 4.7 |
| 2009 | 21.6°C | 13.4°C | 5.2°C | 27.8°C | -2.1°C | 23 mm | 52% | 0.5 m/s | 5.2 |
| 2008 | 17.4°C | 9.6°C | 1.9°C | 25.1°C | -3.1°C | 29 mm | 53% | 0.6 m/s | 4.5 |
| 2007 | 18.3°C | 10.6°C | 2.8°C | 29.7°C | -5.8°C | 49 mm | 57% | 0.5 m/s | 4.5 |
| 2006 | 17.7°C | 10.2°C | 2.6°C | 28.8°C | -3.4°C | 46 mm | 56% | 0.5 m/s | 4.3 |
| 2005 | 18.6°C | 10.8°C | 3.1°C | 27.4°C | -2.6°C | 37 mm | 52% | 0.5 m/s | 4.5 |
| 2004 | 17.0°C | 10.0°C | 3.0°C | 27.5°C | -5.8°C | 50 mm | 61% | 0.5 m/s | 4.3 |
| 2003 | 18.8°C | 10.9°C | 3.1°C | 28.0°C | -5.2°C | 20 mm | 49% | 0.5 m/s | 4.7 |
| 2002 | 18.8°C | 11.1°C | 3.5°C | 28.3°C | -3.1°C | 42 mm | 52% | 0.6 m/s | 4.7 |
| 2001 | 22.3°C | 13.7°C | 5.2°C | 30.0°C | -3.2°C | 27 mm | 45% | 0.5 m/s | 4.9 |
| 2000 | 17.8°C | 9.7°C | 1.7°C | 30.3°C | -9.0°C | 51 mm | 54% | 0.6 m/s | 4.3 |
| 1999 | 16.8°C | 9.1°C | 1.5°C | 24.1°C | -5.3°C | 17 mm | 50% | 0.6 m/s | 4.8 |
| 1998 | 21.1°C | 13.4°C | 5.8°C | 29.8°C | -2.4°C | 37 mm | 56% | 0.5 m/s | 4.7 |
| 1997 | 18.7°C | 11.5°C | 4.3°C | 25.1°C | -1.3°C | 66 mm | 64% | 0.5 m/s | 4.8 |
| 1996 | 15.8°C | 8.8°C | 1.8°C | 25.8°C | -6.2°C | 44 mm | 56% | 0.5 m/s | 4.6 |
| 1995 | 18.2°C | 10.6°C | 3.1°C | 29.0°C | -8.0°C | 34 mm | 58% | 0.5 m/s | 4.5 |
| 1994 | 21.4°C | 13.1°C | 4.7°C | 27.7°C | -1.3°C | 9 mm | 42% | 0.5 m/s | 4.7 |
| 1993 | 15.8°C | 8.6°C | 1.4°C | 23.4°C | -4.8°C | 20 mm | 59% | 0.5 m/s | 4.8 |
| 1992 | 17.3°C | 9.5°C | 1.8°C | 25.0°C | -4.9°C | 49 mm | 51% | 0.6 m/s | 4.4 |
| 1991 | 18.8°C | 11.1°C | 3.4°C | 26.5°C | -2.4°C | 56 mm | 55% | 0.5 m/s | 4.5 |
| 1990 | 22.5°C | 14.0°C | 5.6°C | 28.5°C | 0.3°C | 12 mm | 48% | 0.5 m/s | 5.1 |
| 1989 | 18.6°C | 10.5°C | 2.4°C | 24.9°C | -4.4°C | 31 mm | 49% | 0.6 m/s | 4.9 |
| 1988 | 17.9°C | 9.8°C | 1.7°C | 28.7°C | -4.8°C | 37 mm | 49% | 0.6 m/s | 4.5 |
| 1987 | 20.2°C | 12.0°C | 3.7°C | 27.6°C | -1.7°C | 17 mm | 48% | 0.6 m/s | 5 |
| 1986 | 13.9°C | 7.3°C | 0.8°C | 23.5°C | -4.3°C | 58 mm | 67% | 0.5 m/s | 3.8 |
| 1985 ❄️ | 13.2°C | 6.6°C | 0.0°C | 22.7°C | -9.9°C | 77 mm | 63% | 0.5 m/s | 3.8 |
| 1984 | 15.7°C | 8.2°C | 0.6°C | 25.8°C | -7.7°C | 49 mm | 56% | 0.5 m/s | 4.4 |
| 1983 | 16.5°C | 9.2°C | 2.0°C | 27.6°C | -9.5°C | 80 mm | 60% | 0.5 m/s | — |
| 1982 | 16.3°C | 9.0°C | 1.8°C | 27.0°C | -6.9°C | 77 mm | 61% | 0.5 m/s | — |
| 1981 | 20.6°C | 12.1°C | 3.7°C | 28.8°C | -4.7°C | 33 mm | 48% | 0.5 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 18.8°C with lows near 3.5°C (mean 11.2°C), based on 45 years of NASA POWER data.
September averages 43 mm of rainfall in Bozeman, about average for rainfall. The wettest on record was 95 mm in 2019.
The hottest September reached 33.6°C in 2022. The coldest dipped to -9.9°C in 1985.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 4.7°C. Daytime highs moved from 16.5°C to 21.6°C and overnight lows from 1.6°C to 5.8°C over the same span.
September is one of the warmer months of the year in Bozeman and about average for rainfall, so plan for around 18.8°C daytime highs and 3.5°C at night.
Not quite — September is the 9th coolest month in Bozeman, averaging 11.2°C.
For September in Bozeman, pack warm layers and a jacket for chilly mornings, with typical highs of 18.8°C and lows of 3.5°C.
Relative humidity in September averages 55% — relatively dry.
Average wind speed in September is 0.5 m/s. The windiest September on record averaged 0.6 m/s (1987).
The wettest September on record was 2019 with 95 mm. On average, September sees 43 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 Bozeman 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.
