Weather on September 18
Longmont, CO
55 Years of Data
Avg High
79°F
Avg Low
45°F
Warmest
2000
75°F avg
Coldest
1971
33°F avg
About This Date
September 18th in Longmont, CO typically brings pleasant fall weather, with average highs around 79°F and lows near 45°F — a 34°F daily swing. Over 55 years of records, the warmest September 18th was in 2000 (75°F average), while the coldest was 1971 (33°F) — a 42°F range across recorded history. Precipitation has occurred on 24% of recorded September 18th dates, with snow falling 2% of the time (heaviest snowfall: 4"). The last decade has been 1.5°F warmer on this date compared to 20-30 years ago.
The last decade has been 1.5°F warmer on this date compared to 20-30 years ago.
Planning for September 18th in Longmont, CO? Great weather for outdoor activities.
Warming Trend
1.3°F per decade on this date
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025 | 69° | 46° | 58° | 0.03" | — |
| 2024 | 85° | 46° | 65° | — | — |
| 2023 | 84° | 45° | 64° | — | — |
| 2022 | 81° | 49° | 65° | 0.05" | — |
| 2021 | 69° | 44° | 57° | — | — |
| 2020 | 83° | 46° | 64° | — | — |
| 2019 | 90° | 50° | 70° | — | — |
| 2018 | 93° | 54° | 73° | — | — |
| 2017 | 73° | 47° | 60° | — | — |
| 2016 | 90° | 51° | 70° | — | — |
| 2015 | 74° | 47° | 60° | — | — |
| 2014 | 87° | 51° | 69° | — | — |
| 2013 | 83° | 54° | 68° | 0.05" | — |
| 2012 | 77° | 44° | 61° | — | — |
| 2011 | 76° | 43° | 59° | — | — |
| 2010 | 75° | 51° | 63° | 0.03" | — |
| 2009 | 78° | 44° | 61° | — | — |
| 2008 | 77° | 48° | 63° | — | — |
| 2007 | 78° | 53° | 66° | — | — |
| 2006 | 66° | 37° | 52° | — | — |
| 2005 | 79° | 46° | 62° | — | — |
| 2004 | 90° | 46° | 68° | — | — |
| 2003 | 80° | 36° | 58° | 0.38" | — |
| 2002 | 80° | 48° | 64° | — | — |
| 2001 | 70° | 42° | 56° | — | — |
| 2000warmest | 96° | 54° | 75° | — | — |
| 1999 | 84° | 40° | 62° | — | — |
| 1998 | 90° | 45° | 67° | — | — |
| 1997 | 86° | 44° | 65° | — | — |
| 1996 | 66° | 42° | 54° | 0.53" | — |
| 1995 | 90° | 53° | 71° | — | — |
| 1994 | 83° | 46° | 64° | — | — |
| 1993 | 70° | 45° | 57° | 1.04" | — |
| 1992 | 89° | — | — | — | — |
| 1991 | 67° | 39° | 53° | 0.2" | — |
| 1990 | 63° | 43° | 53° | 0.23" | — |
| 1989 | 88° | 45° | 66° | — | — |
| 1988 | 85° | 39° | 62° | — | — |
| 1987 | 52° | 34° | 43° | 0.05" | — |
| 1986 | 84° | 44° | 64° | — | — |
| 1985 | 84° | 51° | 68° | — | — |
| 1984 | 85° | 40° | 62° | — | — |
| 1983 | 92° | 47° | 69° | — | — |
| 1982 | 52° | 47° | 49° | 0.05" | — |
| 1981 | 76° | 40° | 58° | — | — |
| 1980 | 88° | 43° | 65° | — | — |
| 1979 | 85° | 47° | 66° | — | — |
| 1978 | 73° | 48° | 61° | 0.05" | — |
| 1977 | 83° | 40° | 61° | — | — |
| 1976 | 80° | 47° | 63° | — | — |
| 1975 | 86° | 43° | 64° | — | — |
| 1974 | 78° | 42° | 60° | — | — |
| 1973 | 65° | 38° | 51° | — | — |
| 1972 | 89° | 48° | 69° | — | — |
| 1971coldest | 35° | 30° | 33° | 2.41" | 4" |
55 years of data from LONGMONT 2 ESE