Weather on August 21
Boulder, CO
55 Years of Data
Avg High
86°F
Avg Low
56°F
Warmest
2024
79°F avg
Coldest
2018
61°F avg
About This Date
August 21st in Boulder, CO typically brings warm summer weather, with average highs around 86°F and lows near 56°F — a 30°F daily swing. Over 55 years of records, the warmest August 21st was in 2024 (79°F average), while the coldest was 2018 (61°F) — a 18°F range across recorded history. Rain or other precipitation has occurred on about 31% of August 21st dates historically, with the wettest August 21st recording 0.66" of rain. The last decade has been 1.1°F warmer on this date compared to 20-30 years ago.
The last decade has been 1.1°F warmer on this date compared to 20-30 years ago.
Planning for August 21st in Boulder, CO? Stay hydrated and seek shade during peak afternoon hours. Consider bringing rain gear or an umbrella.
Warming Trend
0.4°F per decade on this date
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025 | 95° | 63° | 79° | — | — |
| 2024warmest | 93° | 64° | 79° | — | — |
| 2023 | 97° | 59° | 78° | — | — |
| 2022 | 81° | 55° | 68° | — | — |
| 2021 | 82° | 54° | 68° | 0.46" | — |
| 2020 | 91° | 61° | 76° | — | — |
| 2019 | 81° | 63° | 72° | — | — |
| 2018coldest | 66° | 55° | 61° | — | — |
| 2017 | 85° | 56° | 70° | — | — |
| 2016 | 90° | 46° | 68° | — | — |
| 2015 | 93° | 53° | 73° | — | — |
| 2014 | 84° | 58° | 71° | 0.28" | — |
| 2013 | 92° | 64° | 78° | 0.46" | — |
| 2012 | 89° | 53° | 71° | — | — |
| 2011 | 90° | 57° | 73° | — | — |
| 2010 | 89° | 56° | 72° | — | — |
| 2009 | 86° | 49° | 67° | — | — |
| 2008 | 92° | 54° | 73° | — | — |
| 2007 | 96° | 57° | 77° | — | — |
| 2006 | 84° | 54° | 69° | — | — |
| 2005 | 84° | 56° | 70° | — | — |
| 2004 | 80° | 49° | 64° | 0.05" | — |
| 2003 | 91° | 62° | 77° | — | — |
| 2002 | 87° | 62° | 75° | 0.18" | — |
| 2001 | 85° | 58° | 71° | — | — |
| 2000 | 79° | 52° | 65° | 0.05" | — |
| 1999 | 84° | 55° | 70° | 0.66" | — |
| 1998 | 85° | 57° | 71° | — | — |
| 1997 | 88° | 57° | 72° | 0.08" | — |
| 1996 | 86° | 59° | 73° | 0.03" | — |
| 1995 | 90° | 59° | 74° | — | — |
| 1994 | 84° | 54° | 69° | — | — |
| 1993 | 84° | 59° | 72° | 0.13" | — |
| 1992 | 83° | 52° | 67° | — | — |
| 1991 | 86° | 54° | 70° | 0.03" | — |
| 1990 | 83° | 55° | 69° | — | — |
| 1989 | 82° | 46° | 64° | — | — |
| 1988 | 85° | 63° | 74° | — | — |
| 1987 | 88° | 63° | 75° | 0.53" | — |
| 1986 | 80° | 55° | 68° | 0.23" | — |
| 1985 | 92° | 57° | 74° | — | — |
| 1984 | 71° | 57° | 64° | 0.51" | — |
| 1983 | 90° | 60° | 75° | — | — |
| 1982 | 84° | 57° | 71° | 0.1" | — |
| 1981 | 90° | 52° | 71° | — | — |
| 1980 | 83° | 49° | 66° | — | — |
| 1979 | 78° | 52° | 65° | — | — |
| 1978 | 88° | 56° | 72° | — | — |
| 1977 | 82° | 55° | 69° | 0.03" | — |
| 1976 | 90° | 59° | 74° | — | — |
| 1975 | 81° | 55° | 68° | 0.03" | — |
| 1974 | 89° | 54° | 71° | — | — |
| 1973 | 93° | 59° | 76° | — | — |
| 1972 | 80° | 59° | 70° | — | — |
| 1971 | 93° | 59° | 76° | — | — |
55 years of data from BOULDER MUNI AP