Weather on September 21
Longmont, CO
55 Years of Data
Avg High
75°F
Avg Low
44°F
Warmest
2005
74°F avg
Coldest
1995
39°F avg
About This Date
September 21st in Longmont, CO typically brings pleasant fall weather, with average highs around 75°F and lows near 44°F — a 31°F daily swing. Over 55 years of records, the warmest September 21st was in 2005 (74°F average), while the coldest was 1995 (39°F) — a 35°F range across recorded history. Rain or other precipitation has occurred on about 27% of September 21st dates historically, with the wettest September 21st recording 2.31" of rain. The last decade has been 8.6°F warmer on this date compared to 20-30 years ago.
The last decade has been 8.6°F warmer on this date compared to 20-30 years ago.
Planning for September 21st in Longmont, CO? Great weather for outdoor activities.
Warming Trend
2.1°F per decade on this date
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025 | 81° | 50° | 65° | 0.03" | — |
| 2024 | 81° | 50° | 65° | — | — |
| 2023 | 81° | 48° | 64° | — | — |
| 2022 | 90° | 52° | 71° | — | — |
| 2021 | 69° | 40° | 54° | 0.13" | — |
| 2020 | 85° | 50° | 67° | — | — |
| 2019 | 88° | 49° | 68° | — | — |
| 2018 | 84° | 51° | 68° | — | — |
| 2017 | 76° | 43° | 59° | — | — |
| 2016 | 84° | 58° | 71° | — | — |
| 2015 | 88° | 48° | 68° | — | — |
| 2014 | 77° | 55° | 66° | — | — |
| 2013 | 79° | 46° | 62° | — | — |
| 2012 | 78° | 49° | 63° | — | — |
| 2011 | 65° | 39° | 52° | — | — |
| 2010 | 79° | 47° | 63° | — | — |
| 2009 | 67° | 40° | 53° | 0.56" | — |
| 2008 | 76° | 49° | 62° | 0.05" | — |
| 2007 | 89° | 59° | 74° | — | — |
| 2006 | 66° | 48° | 57° | 0.46" | — |
| 2005warmest | 86° | 63° | 74° | 0.03" | — |
| 2004 | 83° | 44° | 63° | — | — |
| 2003 | 77° | 39° | 58° | — | — |
| 2002 | 82° | 39° | 61° | — | — |
| 2001 | 80° | 40° | 60° | — | — |
| 2000 | 58° | 34° | 46° | — | — |
| 1999 | 55° | 30° | 43° | 0.38" | — |
| 1998 | 78° | 43° | 60° | 1.27" | — |
| 1997 | 56° | 42° | 49° | 0.03" | — |
| 1996 | 68° | 36° | 52° | — | — |
| 1995coldest | 50° | 29° | 39° | 2.31" | — |
| 1994 | 80° | 52° | 66° | — | — |
| 1993 | 77° | 38° | 57° | — | — |
| 1992 | 83° | — | — | — | — |
| 1991 | 80° | 40° | 60° | — | — |
| 1990 | 68° | 42° | 55° | 0.08" | — |
| 1989 | 76° | 43° | 59° | 0.71" | — |
| 1988 | 83° | 30° | 56° | — | — |
| 1987 | 72° | 37° | 54° | — | — |
| 1986 | 75° | 46° | 61° | — | — |
| 1985 | 75° | 41° | 58° | — | — |
| 1984 | 80° | 48° | 64° | — | — |
| 1983 | 54° | 26° | 40° | — | — |
| 1982 | 72° | 45° | 58° | — | — |
| 1981 | 91° | 54° | 72° | — | — |
| 1980 | 83° | 46° | 64° | — | — |
| 1979 | 71° | 48° | 60° | 0.1" | — |
| 1978 | 55° | 30° | 43° | — | — |
| 1977 | 87° | 47° | 67° | — | — |
| 1976 | 66° | 44° | 55° | — | — |
| 1975 | 59° | 33° | 46° | — | — |
| 1974 | 65° | 41° | 53° | 0.05" | — |
| 1973 | 81° | 47° | 64° | — | — |
| 1972 | 76° | 39° | 57° | — | — |
| 1971 | 60° | 35° | 48° | 0.51" | — |
55 years of data from LONGMONT 2 ESE