Boise County Weather in September
Average highs run from 82°F on September 1 to 71°F on September 30, and lows from 40°F to 32°F. Normal precipitation for the month is 0.77 in over about 3 wet days.
September day by day
The normal high and low for each date, and the record, in °F.
- Normal low
- Normal high
- Record high
- Record low
September at a glance
- Average high
- 77°F
- Average low
- 36°F
- Precipitation
- 0.77 in
- Record high
- 104°FSep 7, 2022
- Record low
- 23°FSep 14, 1970
- Chance of a freeze
- 96%
- Days of 90°F or more
- 2.0
- Daylight
- 13 h 12 min to 11 h 45 min
- Cloud cover
- 44%
- Humidity
- 42%
- Dew point
- 30°F
- Wind
- 4.5 mph
Every day of the month
A wet day has at least 0.01 inch of precipitation; snow means at least 0.1 inch of snowfall.
| Date | Normal high | Normal low | Record high | Record low | Chance wet | Chance of snow |
|---|---|---|---|---|---|---|
| Sep 1 | 82°F | 40°F | 102°F 1945 | 41°F 1977 | 9% | 0% |
| Sep 2 | 81°F | 39°F | 101°F 1950 | 42°F 1999 | 9% | 0% |
| Sep 3 | 81°F | 39°F | 102°F 2022 | 37°F 1956 | 9% | 0% |
| Sep 4 | 81°F | 39°F | 102°F 2020 | 40°F 1969 | 9% | 0% |
| Sep 5 | 80°F | 38°F | 100°F 1963 | 36°F 1969 | 9% | 0% |
| Sep 6 | 80°F | 38°F | 101°F 2022 | 40°F 1945 | 9% | 0% |
| Sep 7 | 80°F | 38°F | 104°F 2022 | 34°F 1976 | 10% | 0% |
| Sep 8 | 79°F | 38°F | 98°F 2024 | 37°F 1946 | 10% | 0% |
| Sep 9 | 79°F | 37°F | 98°F 2021 | 34°F 1970 | 10% | 0% |
| Sep 10 | 79°F | 37°F | 97°F 1990 | 36°F 1989 | 10% | 0% |
| Sep 11 | 78°F | 37°F | 97°F 1963 | 35°F 1982 | 10% | 0% |
| Sep 12 | 78°F | 37°F | 94°F 1963 | 32°F 1970 | 10% | 0% |
| Sep 13 | 78°F | 36°F | 94°F 1945 | 31°F 1970 | 10% | |
| Sep 14 | 77°F | 36°F | 101°F 2000 | 23°F 1970 | 11% | |
| Sep 15 | 77°F | 36°F | 94°F 1995 | 36°F 1970 | 11% | |
| Sep 16 | 77°F | 36°F | 93°F 1943 | 33°F 1965 | 11% | |
| Sep 17 | 76°F | 35°F | 95°F 1981 | 24°F 1965 | 11% | |
| Sep 18 | 76°F | 35°F | 96°F 1981 | 27°F 1965 | 11% | |
| Sep 19 | 75°F | 35°F | 94°F 2008 | 31°F 1978 | 11% | |
| Sep 20 | 75°F | 34°F | 89°F 1966 | 33°F 1983 | 12% | |
| Sep 21 | 75°F | 34°F | 95°F 1967 | 30°F 1993 | 12% | |
| Sep 22 | 74°F | 34°F | 99°F 1966 | 31°F 1955 | 12% | |
| Sep 23 | 74°F | 34°F | 94°F 1987 | 29°F 1984 | 12% | |
| Sep 24 | 73°F | 33°F | 98°F 2011 | 28°F 1984 | 12% | |
| Sep 25 | 73°F | 33°F | 95°F 1963 | 28°F 1972 | 12% | |
| Sep 26 | 73°F | 33°F | 93°F 1963 | 35°F 1961 | 12% | |
| Sep 27 | 72°F | 33°F | 95°F 2022 | 32°F 1945 | 13% | |
| Sep 28 | 72°F | 32°F | 95°F 1963 | 31°F 1999 | 13% | |
| Sep 29 | 71°F | 32°F | 95°F 1992 | 27°F 1954 | 13% | |
| Sep 30 | 71°F | 32°F | 96°F 1992 | 29°F 1954 | 13% |
Chance of rain
- Chance of a wet day
- Chance of snowfall
Sunrise and sunset
Times for 2026, local time (MDT).
- September 1
- sunrise 7:06 AM, sunset 8:18 PM
- September 30
- sunrise 7:40 AM, sunset 7:25 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USC00104442 (Idaho City), public domain. Records: NOAA GHCN-Daily, station USW00024131, every year on file, quality-flagged values removed. Cloud, humidity, wind and sunshine: NASA POWER (MERRA-2, CERES and GEWEX SRB), 1991-2020. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division: POWER Daily API v2, accessed 2026-09-25. Sun and moon: computed with the NOAA solar equations and Meeus.