Boulder Weather in September
Average highs run from 77°F on September 1 to 66°F on September 30, and lows from 42°F to 34°F. Normal precipitation for the month is 1.10 in over about 7 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
- 72°F
- Average low
- 38°F
- Precipitation
- 1.10 in
- Record high
- 96°FSep 3, 2022
- Record low
- 3°FSep 24, 1926
- Chance of a freeze
- 98%
- Days of 90°F or more
- 0.8
- Daylight
- 13 h 18 min to 11 h 44 min
- Cloud cover
- 52%
- Humidity
- 55%
- Dew point
- 35°F
- Wind
- 5.8 mph
Every day of the month
A wet day has at least 0.01 inch of precipitation.
| Date | Normal high | Normal low | Record high | Record low | Chance wet |
|---|---|---|---|---|---|
| Sep 1 | 77°F | 42°F | 92°F 1998 | 26°F 2006 | 23% |
| Sep 2 | 77°F | 42°F | 90°F 1950 | 25°F 1959 | 23% |
| Sep 3 | 77°F | 42°F | 96°F 2022 | 23°F 1958 | 23% |
| Sep 4 | 76°F | 41°F | 93°F 1998 | 24°F 1969 | 23% |
| Sep 5 | 76°F | 41°F | 93°F 1998 | 23°F 1969 | 23% |
| Sep 6 | 76°F | 41°F | 90°F 2022 | 26°F 1948 | 23% |
| Sep 7 | 75°F | 41°F | 91°F 2022 | 18°F 1992 | 23% |
| Sep 8 | 75°F | 40°F | 90°F 1979 | 25°F 2020 | 23% |
| Sep 9 | 75°F | 40°F | 87°F 1981 | 20°F 1959 | 23% |
| Sep 10 | 74°F | 40°F | 87°F 1966 | 24°F 1921 | 23% |
| Sep 11 | 74°F | 40°F | 87°F 1981 | 24°F 1921 | 23% |
| Sep 12 | 74°F | 39°F | 87°F 1981 | 18°F 1989 | 23% |
| Sep 13 | 73°F | 39°F | 87°F 1981 | 22°F 1974 | 23% |
| Sep 14 | 73°F | 39°F | 87°F 1948 | 21°F 1970 | 23% |
| Sep 15 | 72°F | 38°F | 93°F 2000 | 22°F 1965 | 23% |
| Sep 16 | 72°F | 38°F | 86°F 1998 | 18°F 1965 | 23% |
| Sep 17 | 72°F | 38°F | 90°F 1981 | 9°F 1965 | 23% |
| Sep 18 | 71°F | 38°F | 91°F 1981 | 6°F 1965 | 23% |
| Sep 19 | 71°F | 37°F | 86°F 1898 | 16°F 1983 | 23% |
| Sep 20 | 70°F | 37°F | 83°F 1917 | 8°F 1983 | 23% |
| Sep 21 | 70°F | 37°F | 85°F 1918 | 21°F 1895 | 23% |
| Sep 22 | 69°F | 36°F | 86°F 1987 | 19°F 1993 | 23% |
| Sep 23 | 69°F | 36°F | 87°F 1987 | 15°F 1934 | 23% |
| Sep 24 | 69°F | 36°F | 85°F 2001 | 3°F 1926 | 23% |
| Sep 25 | 68°F | 35°F | 86°F 2001 | 13°F 1926 | 23% |
| Sep 26 | 68°F | 35°F | 84°F 1963 | 18°F 1933 | 22% |
| Sep 27 | 67°F | 35°F | 83°F 1963 | 16°F 1935 | 22% |
| Sep 28 | 67°F | 34°F | 84°F 2024 | 17°F 1985 | 22% |
| Sep 29 | 66°F | 34°F | 84°F 1963 | 10°F 1985 | 22% |
| Sep 30 | 66°F | 34°F | 84°F 1992 | 13°F 1985 | 22% |
Chance of rain
- Chance of a wet day
Sunrise and sunset
Times for 2026, local time (MDT).
- September 1
- sunrise 6:49 AM, sunset 8:07 PM
- September 30
- sunrise 7:26 AM, sunset 7:10 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USC00241008 (Boulder), public domain. Records: NOAA GHCN-Daily, station USW00024135, 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 2026-09-24. Sun and moon: computed with the NOAA solar equations and Meeus.