September is one of the warmer months of the year in Missoula, with average highs near 19.6°C and lows around 4.7°C (mean 12.2°C). It is one of the drier months, averaging 42 mm of rainfall and 58% relative humidity across the period.
September is one of the warmer months of the year in Missoula. Across 45 years of records, the warmest September in Missoula was 2025 — when the month averaged 16.8°C — while the coldest was 1985 at 7.1°C. Typical September days reach 19.6°C with nights near 4.7°C. The long-term trend is warming, about 0.8°C per decade.
September is one of the drier months in Missoula, averaging 42 mm of rainfall. The wettest September on record was 1985 with 115 mm, while the driest was 1990 at 4 mm.
Relative humidity in Missoula during September averages 58%. The most humid September was 1986 at 76%, and the least humid was 1994 at 45%.
September receives about 4.4 kWh/m²/day of solar energy in Missoula. The sunniest September was 1990 at 5.4 kWh/m²/day, and the cloudiest was 1986 at 3.4.
Average wind speed in Missoula during September is 0.3 m/s. The windiest Septembers were 2012, 2020 and 2021, among others at 0.4 m/s, while the calmest were 2013, 2016 and 2019, among others at 0.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 10.3°C | 12.4°C | 12.0°C | 12.5°C | 14.4°C | +4.1°C |
| Avg High | 17.5°C | 20.1°C | 19.6°C | 19.6°C | 22.0°C | +4.5°C |
| Avg Low | 3.0°C | 4.6°C | 4.4°C | 5.3°C | 6.9°C | +3.9°C |
| Avg Rain | 51 mm | 33 mm | 45 mm | 42 mm | 40 mm | -11 mm |
September temperatures in Missoula have risen by about 5.1°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -7.6°C (1985) to a record high of 35.1°C (2022).
Rainfall in September is one of the drier months, averaging 42 mm, with a wettest year of 115 mm.
One of the best times to visit Missoula
September is one of the best times to visit Missoula. Expect days averaging 19.6°C and nights around 4.7°C (mean 12.2°C) — warmer than Missoula's yearly average — with moderate rainfall (42 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 🔥 | 24.8°C | 16.8°C | 8.8°C | 33.8°C | 4.2°C | 32 mm | 55% | 0.3 m/s | 4.4 |
| 2024 | 21.8°C | 14.5°C | 7.1°C | 30.2°C | -2.8°C | 46 mm | 60% | 0.3 m/s | 4.1 |
| 2023 | 19.6°C | 12.8°C | 6.1°C | 26.6°C | 0.3°C | 52 mm | 62% | 0.3 m/s | 4 |
| 2022 | 23.1°C | 15.5°C | 7.9°C | 35.1°C | 0.6°C | 50 mm | 53% | 0.3 m/s | 4.4 |
| 2021 | 20.8°C | 13.3°C | 5.8°C | 31.3°C | -0.4°C | 24 mm | 53% | 0.4 m/s | 4.6 |
| 2020 | 21.6°C | 13.7°C | 5.9°C | 31.5°C | -2.8°C | 34 mm | 55% | 0.4 m/s | 4.2 |
| 2019 | 18.1°C | 11.9°C | 5.6°C | 31.0°C | -6.6°C | 83 mm | 68% | 0.2 m/s | 3.8 |
| 2018 | 18.0°C | 11.1°C | 4.2°C | 28.8°C | -0.5°C | 17 mm | 60% | 0.3 m/s | 4.8 |
| 2017 | 18.6°C | 11.7°C | 4.9°C | 30.7°C | -3.6°C | 50 mm | 61% | 0.3 m/s | 3.7 |
| 2016 | 17.7°C | 10.8°C | 3.9°C | 27.3°C | -3.8°C | 49 mm | 65% | 0.2 m/s | 4 |
| 2015 | 19.8°C | 12.6°C | 5.4°C | 28.7°C | 0.8°C | 36 mm | 57% | 0.3 m/s | 4.5 |
| 2014 | 20.1°C | 12.6°C | 5.0°C | 28.2°C | -4.8°C | 32 mm | 58% | 0.3 m/s | 4.5 |
| 2013 | 19.9°C | 13.4°C | 6.8°C | 32.2°C | -3.5°C | 67 mm | 65% | 0.2 m/s | 3.7 |
| 2012 | 22.3°C | 14.0°C | 5.8°C | 27.2°C | -0.1°C | 5 mm | 46% | 0.4 m/s | 5 |
| 2011 | 23.3°C | 14.8°C | 6.2°C | 29.7°C | 0.6°C | 20 mm | 49% | 0.3 m/s | 5 |
| 2010 | 18.4°C | 11.6°C | 4.7°C | 26.4°C | -1.1°C | 60 mm | 68% | 0.3 m/s | 4.2 |
| 2009 | 23.2°C | 14.7°C | 6.1°C | 30.5°C | -1.4°C | 12 mm | 51% | 0.3 m/s | 5 |
| 2008 | 18.9°C | 11.3°C | 3.8°C | 27.1°C | -2.0°C | 40 mm | 56% | 0.4 m/s | 4.8 |
| 2007 | 19.0°C | 11.3°C | 3.5°C | 30.9°C | -5.1°C | 49 mm | 57% | 0.3 m/s | 4.6 |
| 2006 | 20.1°C | 12.4°C | 4.7°C | 32.3°C | -0.7°C | 48 mm | 57% | 0.3 m/s | 4.4 |
| 2005 | 18.1°C | 10.8°C | 3.5°C | 27.2°C | -1.6°C | 56 mm | 58% | 0.3 m/s | 4.4 |
| 2004 | 16.2°C | 10.1°C | 3.9°C | 27.7°C | -3.4°C | 79 mm | 73% | 0.3 m/s | 3.7 |
| 2003 | 20.4°C | 12.6°C | 4.8°C | 31.6°C | -2.0°C | 36 mm | 54% | 0.3 m/s | 4.6 |
| 2002 | 19.6°C | 12.0°C | 4.5°C | 30.2°C | -0.8°C | 35 mm | 56% | 0.3 m/s | 4.6 |
| 2001 | 23.4°C | 14.5°C | 5.7°C | 31.0°C | -0.7°C | 12 mm | 46% | 0.4 m/s | 5.1 |
| 2000 | 17.5°C | 10.5°C | 3.4°C | 33.2°C | -7.1°C | 78 mm | 62% | 0.3 m/s | 3.9 |
| 1999 | 19.0°C | 11.0°C | 3.0°C | 26.8°C | -4.7°C | 18 mm | 49% | 0.3 m/s | 5 |
| 1998 | 23.3°C | 15.4°C | 7.5°C | 33.0°C | 0.2°C | 27 mm | 54% | 0.3 m/s | 4.7 |
| 1997 | 20.8°C | 12.8°C | 4.9°C | 28.9°C | -0.8°C | 41 mm | 63% | 0.3 m/s | 4.2 |
| 1996 | 16.6°C | 9.6°C | 2.6°C | 28.1°C | -4.2°C | 60 mm | 69% | 0.3 m/s | 4 |
| 1995 | 18.9°C | 11.7°C | 4.5°C | 32.0°C | -6.5°C | 68 mm | 63% | 0.3 m/s | 4.5 |
| 1994 | 22.8°C | 14.6°C | 6.4°C | 29.0°C | 1.5°C | 13 mm | 45% | 0.4 m/s | 4.7 |
| 1993 | 17.6°C | 10.0°C | 2.4°C | 24.9°C | -2.6°C | 24 mm | 63% | 0.3 m/s | 5.1 |
| 1992 | 17.0°C | 9.9°C | 2.7°C | 28.3°C | -3.2°C | 51 mm | 59% | 0.3 m/s | 4.2 |
| 1991 | 20.6°C | 12.7°C | 4.8°C | 28.7°C | 0.0°C | 26 mm | 53% | 0.3 m/s | 4.9 |
| 1990 | 24.6°C | 15.9°C | 7.3°C | 30.4°C | 2.4°C | 4 mm | 47% | 0.4 m/s | 5.4 |
| 1989 | 19.7°C | 11.6°C | 3.6°C | 27.5°C | -3.8°C | 37 mm | 57% | 0.4 m/s | 5 |
| 1988 | 19.1°C | 11.3°C | 3.4°C | 32.9°C | -3.4°C | 33 mm | 54% | 0.3 m/s | 4.4 |
| 1987 | 22.0°C | 14.1°C | 6.1°C | 30.9°C | -0.1°C | 7 mm | 46% | 0.4 m/s | 5 |
| 1986 | 13.8°C | 8.0°C | 2.1°C | 24.8°C | -2.7°C | 90 mm | 76% | 0.2 m/s | 3.4 |
| 1985 ❄️ 🌧️ | 13.3°C | 7.1°C | 0.8°C | 24.8°C | -7.6°C | 115 mm | 73% | 0.2 m/s | 3.8 |
| 1984 | 15.8°C | 8.7°C | 1.6°C | 27.5°C | -6.9°C | 42 mm | 59% | 0.3 m/s | 4.1 |
| 1983 | 15.6°C | 8.6°C | 1.6°C | 26.8°C | -5.9°C | 57 mm | 66% | 0.3 m/s | — |
| 1982 | 17.7°C | 10.3°C | 2.9°C | 29.7°C | -5.2°C | 52 mm | 62% | 0.3 m/s | — |
| 1981 | 20.5°C | 12.6°C | 4.7°C | 32.4°C | -2.6°C | 29 mm | 51% | 0.3 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 19.6°C with lows near 4.7°C (mean 12.2°C), based on 45 years of NASA POWER data.
September averages 42 mm of rainfall in Missoula, one of the drier months. The wettest on record was 115 mm in 1985.
The hottest September reached 35.1°C in 2022. The coldest dipped to -7.6°C in 1985.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 5.1°C. Daytime highs moved from 16.6°C to 22°C and overnight lows from 2.3°C to 7.1°C over the same span.
September is one of the warmer months of the year in Missoula and one of the drier months, so plan for around 19.6°C daytime highs and 4.7°C at night.
Not quite — September is the 9th coolest month in Missoula, averaging 12.2°C.
For September in Missoula, pack warm layers and a jacket for chilly mornings, with typical highs of 19.6°C and lows of 4.7°C.
Relative humidity in September averages 58% — moderately humid.
Average wind speed in September is 0.3 m/s. The windiest September on record averaged 0.4 m/s (1987).
The wettest September on record was 1985 with 115 mm. On average, September sees 42 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 Missoula 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.
