September is one of the warmer months of the year in Idaho Falls, with average highs near 22.3°C and lows around 7.4°C (mean 14.9°C). It is about average for rainfall, averaging 35 mm of rainfall and 46% relative humidity across the period.
September is one of the warmer months of the year in Idaho Falls. Across 45 years of records, the warmest September in Idaho Falls was 2022 — when the month averaged 18.1°C — while the coldest was 1985 at 10.6°C. Typical September days reach 22.3°C with nights near 7.4°C. The long-term trend is warming, about 0.6°C per decade.
September is about average for rainfall in Idaho Falls, averaging 35 mm of rainfall. The wettest September on record was 2019 with 90 mm, while the driest was 1987 at 1 mm.
Relative humidity in Idaho Falls during September averages 46%. The most humid September was 2017 at 58%, and the least humid was 1994 at 32%.
September receives about 5 kWh/m²/day of solar energy in Idaho Falls. The sunniest September was 1999 at 5.6 kWh/m²/day, and the cloudiest was 2013 at 4.2.
Average wind speed in Idaho Falls during September is 2.2 m/s. The windiest September was 2013 at 2.7 m/s, while the calmest was 1990 at 1.8 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 13.4°C | 14.7°C | 14.8°C | 15.2°C | 16.6°C | +3.2°C |
| Avg High | 21.0°C | 22.2°C | 22.5°C | 22.4°C | 24.2°C | +3.2°C |
| Avg Low | 5.9°C | 7.3°C | 7.1°C | 8.0°C | 9.0°C | +3.1°C |
| Avg Rain | 34 mm | 27 mm | 30 mm | 49 mm | 36 mm | +2 mm |
September temperatures in Idaho Falls have risen by about 3.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -6.7°C (1983) to a record high of 35.3°C (2022).
Rainfall in September is about average for rainfall, averaging 35 mm, with a wettest year of 90 mm.
One of the best times to visit Idaho Falls
September is one of the best times to visit Idaho Falls. Expect days averaging 22.3°C and nights around 7.4°C (mean 14.9°C) — warmer than Idaho Falls's yearly average — with moderate rainfall (35 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 | 24.6°C | 17.4°C | 10.2°C | 32.0°C | 4.6°C | 32 mm | 48% | 2 m/s | 4.9 |
| 2024 | 24.8°C | 17.1°C | 9.3°C | 31.3°C | 3.0°C | 40 mm | 47% | 2.2 m/s | 5 |
| 2023 | 22.6°C | 15.6°C | 8.7°C | 27.8°C | 1.3°C | 63 mm | 55% | 2.1 m/s | 4.7 |
| 2022 🔥 | 25.8°C | 18.1°C | 10.3°C | 35.3°C | 4.1°C | 39 mm | 43% | 2.2 m/s | 5.1 |
| 2021 | 23.7°C | 15.9°C | 8.0°C | 32.2°C | 1.4°C | 22 mm | 40% | 2.3 m/s | 5.3 |
| 2020 | 23.7°C | 15.7°C | 7.7°C | 33.4°C | -2.4°C | 22 mm | 43% | 2.2 m/s | 5.3 |
| 2019 🌧️ | 20.6°C | 14.3°C | 8.1°C | 33.1°C | -3.0°C | 90 mm | 56% | 2.5 m/s | 4.4 |
| 2018 | 23.4°C | 15.6°C | 7.7°C | 29.3°C | 1.4°C | 2 mm | 40% | 2.2 m/s | 5.5 |
| 2017 | 19.9°C | 13.5°C | 7.1°C | 31.4°C | -2.5°C | 87 mm | 58% | 2.1 m/s | 4.3 |
| 2016 | 20.8°C | 14.2°C | 7.6°C | 31.1°C | 2.4°C | 72 mm | 54% | 2.3 m/s | 4.6 |
| 2015 | 23.7°C | 16.3°C | 8.9°C | 29.4°C | 2.5°C | 54 mm | 46% | 2.4 m/s | 5.2 |
| 2014 | 22.6°C | 15.1°C | 7.5°C | 28.5°C | -2.9°C | 75 mm | 55% | 2.4 m/s | 5.1 |
| 2013 | 21.5°C | 15.3°C | 9.1°C | 31.5°C | 0.2°C | 57 mm | 57% | 2.7 m/s | 4.2 |
| 2012 | 24.0°C | 16.2°C | 8.4°C | 29.0°C | 4.3°C | 21 mm | 41% | 1.9 m/s | 5.3 |
| 2011 | 24.5°C | 16.5°C | 8.5°C | 28.2°C | 4.7°C | 14 mm | 46% | 2 m/s | 5.4 |
| 2010 | 23.4°C | 15.3°C | 7.1°C | 29.0°C | 1.6°C | 14 mm | 41% | 2.4 m/s | 5.3 |
| 2009 | 25.2°C | 17.2°C | 9.2°C | 30.2°C | 0.9°C | 18 mm | 43% | 2 m/s | 5.3 |
| 2008 | 22.5°C | 14.5°C | 6.5°C | 28.2°C | 1.8°C | 11 mm | 41% | 2 m/s | 5.3 |
| 2007 | 21.9°C | 14.3°C | 6.8°C | 32.0°C | -2.7°C | 36 mm | 46% | 2.4 m/s | 4.8 |
| 2006 | 20.9°C | 13.4°C | 6.0°C | 29.6°C | -1.9°C | 54 mm | 48% | 2 m/s | 4.7 |
| 2005 | 21.4°C | 13.8°C | 6.2°C | 30.1°C | -0.7°C | 40 mm | 47% | 2.3 m/s | 4.8 |
| 2004 | 21.0°C | 13.7°C | 6.3°C | 29.7°C | -1.3°C | 35 mm | 49% | 2.4 m/s | 4.6 |
| 2003 | 22.3°C | 14.6°C | 6.8°C | 30.9°C | -1.1°C | 21 mm | 41% | 2.1 m/s | 5 |
| 2002 | 22.1°C | 14.8°C | 7.6°C | 32.0°C | 0.1°C | 51 mm | 45% | 2.4 m/s | 4.9 |
| 2001 | 25.2°C | 17.2°C | 9.2°C | 32.2°C | -0.4°C | 18 mm | 38% | 2.3 m/s | 5.3 |
| 2000 | 22.2°C | 14.3°C | 6.4°C | 32.5°C | -3.6°C | 17 mm | 43% | 2.4 m/s | 5.1 |
| 1999 | 21.2°C | 13.2°C | 5.2°C | 26.2°C | -5.2°C | 14 mm | 42% | 2.1 m/s | 5.6 |
| 1998 | 23.3°C | 16.4°C | 9.5°C | 30.9°C | 3.5°C | 51 mm | 53% | 1.9 m/s | 4.9 |
| 1997 | 21.7°C | 15.1°C | 8.4°C | 29.4°C | 2.6°C | 46 mm | 58% | 2.3 m/s | 5 |
| 1996 | 19.6°C | 12.2°C | 4.9°C | 28.6°C | -2.4°C | 33 mm | 48% | 2.3 m/s | 4.9 |
| 1995 | 22.2°C | 14.9°C | 7.7°C | 32.8°C | -4.2°C | 16 mm | 46% | 2.1 m/s | 5.3 |
| 1994 | 24.7°C | 16.9°C | 9.1°C | 31.0°C | 2.6°C | 25 mm | 32% | 2.2 m/s | 5.2 |
| 1993 | 20.4°C | 13.1°C | 5.8°C | 26.8°C | -0.1°C | 11 mm | 46% | 2.1 m/s | 5.2 |
| 1992 | 21.4°C | 13.6°C | 5.9°C | 27.8°C | 0.6°C | 18 mm | 40% | 2.6 m/s | 4.9 |
| 1991 | 21.7°C | 14.2°C | 6.7°C | 29.4°C | -0.7°C | 34 mm | 48% | 1.9 m/s | 4.9 |
| 1990 | 25.6°C | 17.9°C | 10.1°C | 31.7°C | 4.8°C | 24 mm | 41% | 1.8 m/s | 5.1 |
| 1989 | 22.5°C | 14.4°C | 6.4°C | 27.8°C | 0.4°C | 28 mm | 42% | 2.3 m/s | 5.4 |
| 1988 | 22.1°C | 13.8°C | 5.6°C | 31.6°C | -1.3°C | 8 mm | 37% | 2.4 m/s | 4.9 |
| 1987 | 24.2°C | 15.7°C | 7.3°C | 31.2°C | 1.5°C | 1 mm | 33% | 2 m/s | 5.5 |
| 1986 | 17.4°C | 11.0°C | 4.5°C | 26.7°C | -2.9°C | 54 mm | 57% | 2.2 m/s | 4.3 |
| 1985 ❄️ | 17.6°C | 10.6°C | 3.7°C | 26.1°C | -6.4°C | 57 mm | 51% | 2.6 m/s | 4.6 |
| 1984 | 19.9°C | 12.3°C | 4.6°C | 28.6°C | -3.9°C | 26 mm | 49% | 2.3 m/s | 4.7 |
| 1983 | 21.1°C | 13.8°C | 6.5°C | 31.1°C | -6.7°C | 62 mm | 51% | 2.6 m/s | — |
| 1982 | 20.3°C | 13.2°C | 6.2°C | 29.2°C | -1.5°C | 66 mm | 55% | 2.2 m/s | — |
| 1981 | 24.2°C | 16.1°C | 8.0°C | 30.3°C | -1.5°C | 7 mm | 37% | 2.2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 22.3°C with lows near 7.4°C (mean 14.9°C), based on 45 years of NASA POWER data.
September averages 35 mm of rainfall in Idaho Falls, about average for rainfall. The wettest on record was 90 mm in 2019.
The hottest September reached 35.3°C in 2022. The coldest dipped to -6.7°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 3.6°C. Daytime highs moved from 20.6°C to 24.3°C and overnight lows from 5.8°C to 9.3°C over the same span.
September is one of the warmer months of the year in Idaho Falls and about average for rainfall, so plan for around 22.3°C daytime highs and 7.4°C at night.
Not quite — September is the 9th coolest month in Idaho Falls, averaging 14.9°C.
For September in Idaho Falls, pack warm layers and a jacket for chilly mornings, with typical highs of 22.3°C and lows of 7.4°C.
Relative humidity in September averages 46% — relatively dry.
Average wind speed in September is 2.2 m/s. The windiest September on record averaged 2.7 m/s (2013).
The wettest September on record was 2019 with 90 mm. On average, September sees 35 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 Idaho Falls 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.
