Longmont Weather in September
Average highs run from 85°F on September 1 to 74°F on September 30, and lows from 51°F to 39°F. Normal precipitation for the month is 1.26 in over about 6 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
- 80°F
- Average low
- 46°F
- Precipitation
- 1.26 in
- Record high
- 101°FSep 6, 2020
- Record low
- 18°FSep 30, 1985
- Chance of a freeze
- 30%
- Days of 90°F or more
- 5.8
- Daylight
- 13 h 04 min to 11 h 48 min
- Cloud cover
- 46%
- Humidity
- 43%
- Dew point
- 37°F
- Wind
- 7.2 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 | 85°F | 51°F | 99°F 1960 | 38°F 1950 | 21% | 0% |
| Sep 2 | 85°F | 51°F | 100°F 1995 | 36°F 1952 | 21% | 0% |
| Sep 3 | 85°F | 51°F | 99°F 2019 | 34°F 1934 | 21% | 0% |
| Sep 4 | 84°F | 50°F | 100°F 1995 | 37°F 1921 | 21% | 0% |
| Sep 5 | 84°F | 50°F | 98°F 1998 | 35°F 1918 | 21% | 0% |
| Sep 6 | 84°F | 50°F | 101°F 2020 | 36°F 1921 | 21% | 0% |
| Sep 7 | 84°F | 49°F | 96°F 1982 | 36°F 1922 | 21% | 0% |
| Sep 8 | 83°F | 49°F | 96°F 1988 | 28°F 1929 | 21% | 0% |
| Sep 9 | 83°F | 49°F | 98°F 2022 | 31°F 1941 | 21% | 0% |
| Sep 10 | 83°F | 48°F | 96°F 1979 | 30°F 1962 | 21% | 0% |
| Sep 11 | 82°F | 48°F | 96°F 1994 | 31°F 1916 | 21% | 0% |
| Sep 12 | 82°F | 48°F | 98°F 1939 | 32°F 1912 | 21% | |
| Sep 13 | 82°F | 47°F | 96°F 1895 | 30°F 1993 | 21% | |
| Sep 14 | 81°F | 47°F | 97°F 1990 | 27°F 1993 | 21% | |
| Sep 15 | 81°F | 46°F | 94°F 1956 | 28°F 1993 | 21% | |
| Sep 16 | 81°F | 46°F | 95°F 1895 | 32°F 1951 | 21% | |
| Sep 17 | 80°F | 46°F | 98°F 2000 | 29°F 1965 | 21% | |
| Sep 18 | 80°F | 45°F | 98°F 1895 | 30°F 1965 | 21% | |
| Sep 19 | 79°F | 45°F | 94°F 1998 | 20°F 1971 | 21% | |
| Sep 20 | 79°F | 44°F | 92°F 1980 | 23°F 1971 | 21% | |
| Sep 21 | 78°F | 44°F | 93°F 1949 | 26°F 1983 | 21% | |
| Sep 22 | 78°F | 43°F | 91°F 1915 | 23°F 1995 | 21% | |
| Sep 23 | 78°F | 43°F | 90°F 1947 | 24°F 1995 | 21% | |
| Sep 24 | 77°F | 42°F | 91°F 1992 | 21°F 1926 | 21% | |
| Sep 25 | 77°F | 42°F | 90°F 1992 | 24°F 2000 | 20% | |
| Sep 26 | 76°F | 41°F | 91°F 1949 | 24°F 2000 | 20% | |
| Sep 27 | 76°F | 41°F | 92°F 2001 | 23°F 1996 | 20% | |
| Sep 28 | 75°F | 40°F | 92°F 1953 | 22°F 1984 | 20% | |
| Sep 29 | 75°F | 40°F | 92°F 1994 | 19°F 1985 | 20% | |
| Sep 30 | 74°F | 39°F | 92°F 1994 | 18°F 1985 | 20% |
Chance of rain
- Chance of a wet day
- Chance of snowfall
Sunrise and sunset
Times for 2026, local time (MDT).
- September 1
- sunrise 6:28 AM, sunset 7:32 PM
- September 30
- sunrise 6:56 AM, sunset 6:44 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USC00055116 (Longmont 2 Ese), public domain. Records: NOAA GHCN-Daily, station USC00055116, 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.