Weather on September 20
Longmont, CO
55 Years of Data
Avg High
77°F
Avg Low
44°F
Warmest
1980
71°F avg
Coldest
1971
39°F avg
About This Date
September 20th in Longmont, CO typically brings pleasant fall weather, with average highs around 77°F and lows near 44°F — a 33°F daily swing. Over 55 years of records, the warmest September 20th was in 1980 (71°F average), while the coldest was 1971 (39°F) — a 32°F range across recorded history. Rain or other precipitation has occurred on about 22% of September 20th dates historically, with the wettest September 20th recording 1.24" of rain. The last decade has been 9.5°F warmer on this date compared to 20-30 years ago.
The last decade has been 9.5°F warmer on this date compared to 20-30 years ago.
Planning for September 20th 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 | 79° | 46° | 62° | — | — |
| 2024 | 83° | 48° | 65° | — | — |
| 2023 | 77° | 47° | 62° | — | — |
| 2022 | 90° | 51° | 70° | — | — |
| 2021 | 85° | 50° | 67° | — | — |
| 2020 | 88° | 54° | 71° | — | — |
| 2019 | 84° | 49° | 66° | — | — |
| 2018 | 82° | 53° | 68° | 0.13" | — |
| 2017 | 87° | 43° | 65° | — | — |
| 2016 | 85° | 55° | 70° | — | — |
| 2015 | 85° | 47° | 66° | — | — |
| 2014 | 78° | 53° | 66° | — | — |
| 2013 | 71° | 43° | 57° | — | — |
| 2012 | 81° | 48° | 64° | — | — |
| 2011 | 76° | 44° | 60° | — | — |
| 2010 | 90° | 53° | 71° | — | — |
| 2009 | 81° | 50° | 65° | — | — |
| 2008 | 77° | 47° | 62° | — | — |
| 2007 | 88° | 47° | 67° | — | — |
| 2006 | 76° | 41° | 58° | — | — |
| 2005 | 88° | 48° | 68° | — | — |
| 2004 | 92° | 49° | 70° | — | — |
| 2003 | 72° | 41° | 56° | — | — |
| 2002 | 72° | 35° | 53° | — | — |
| 2001 | 76° | 39° | 57° | — | — |
| 2000 | 79° | 38° | 58° | 1.24" | — |
| 1999 | 50° | 37° | 44° | 0.74" | — |
| 1998 | 87° | 45° | 66° | 0.03" | — |
| 1997 | 59° | 41° | 50° | 0.99" | — |
| 1996 | 64° | 33° | 49° | — | — |
| 1995 | 54° | 44° | 49° | 0.13" | — |
| 1994 | 79° | 48° | 63° | — | — |
| 1993 | 73° | 35° | 54° | — | — |
| 1992 | 77° | — | — | — | — |
| 1991 | 68° | 36° | 52° | — | — |
| 1990 | 75° | 43° | 59° | — | — |
| 1989 | 80° | 50° | 65° | — | — |
| 1988 | 74° | 30° | 52° | — | — |
| 1987 | 73° | 33° | 53° | — | — |
| 1986 | 72° | 46° | 59° | — | — |
| 1985 | 57° | 44° | 51° | 0.03" | — |
| 1984 | 92° | 46° | 69° | — | — |
| 1983 | 89° | 29° | 59° | 0.28" | — |
| 1982 | 70° | 48° | 59° | 0.03" | — |
| 1981 | 85° | 49° | 67° | — | — |
| 1980warmest | 92° | 50° | 71° | 0.89" | — |
| 1979 | 86° | 48° | 67° | — | — |
| 1978 | 55° | 36° | 45° | 0.23" | — |
| 1977 | 79° | 45° | 62° | — | — |
| 1976 | 59° | 50° | 55° | 0.51" | — |
| 1975 | 65° | 32° | 48° | — | — |
| 1974 | 68° | 41° | 55° | — | — |
| 1973 | 85° | 44° | 64° | — | — |
| 1972 | 84° | 48° | 66° | — | — |
| 1971coldest | 55° | 23° | 39° | — | — |
55 years of data from LONGMONT 2 ESE