Weather on August 21
Rancho Cucamonga, CA
55 Years of Data
Avg High
91°F
Avg Low
63°F
Warmest
1982
90°F avg
Coldest
1975
65°F avg
About This Date
August 21st in Rancho Cucamonga, CA typically brings hot summer weather, with average highs around 91°F and lows near 63°F — a 28°F daily swing. Over 42 years of records, the warmest August 21st was in 1982 (90°F average), while the coldest was 1975 (65°F) — a 25°F range across recorded history. Rain or other precipitation has occurred on about 2% of August 21st dates historically, with the wettest August 21st recording 0.58" of rain. The last decade has been 4.2°F warmer on this date compared to 20-30 years ago.
The last decade has been 4.2°F warmer on this date compared to 20-30 years ago.
Planning for August 21st in Rancho Cucamonga, CA? Stay hydrated and seek shade during peak afternoon hours.
Warming Trend
1.1°F per decade on this date
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025 | 103° | 74° | 88° | — | — |
| 2024 | 99° | 69° | 84° | — | — |
| 2023 | 83° | 62° | 72° | 0.58" | — |
| 2022 | 87° | 65° | 76° | — | — |
| 2021 | 77° | 65° | 71° | — | — |
| 2020 | 103° | 74° | 88° | — | — |
| 2019 | 98° | 66° | 82° | — | — |
| 2018 | 91° | 67° | 79° | — | — |
| 2017 | 90° | 64° | 77° | — | — |
| 2016 | 93° | 64° | 79° | — | — |
| 2015 | 88° | 66° | 77° | — | — |
| 2014 | 92° | 64° | 78° | — | — |
| 2013 | 100° | 66° | 83° | — | — |
| 2012 | 93° | 70° | 81° | — | — |
| 2011 | 87° | 57° | 72° | — | — |
| 2010 | 97° | 66° | 81° | — | — |
| 2009 | 86° | 64° | 75° | — | — |
| 2008 | 90° | 64° | 77° | — | — |
| 2007 | 99° | 68° | 83° | — | — |
| 2006 | 94° | 60° | 77° | — | — |
| 2005 | 94° | 61° | 77° | — | — |
| 2004 | 82° | 61° | 71° | — | — |
| 2003 | 89° | 66° | 78° | — | — |
| 2002 | 80° | 60° | 70° | — | — |
| 2001 | 84° | 60° | 72° | — | — |
| 2000 | 90° | 61° | 75° | — | — |
| 1999 | 98° | 59° | 79° | — | — |
| 1998 | 100° | 63° | 81° | — | — |
| 1984 | 98° | 66° | 82° | — | — |
| 1983 | 80° | 62° | 71° | — | — |
| 1982warmest | 108° | 72° | 90° | — | — |
| 1981 | 104° | 62° | 83° | — | — |
| 1980 | 90° | 54° | 72° | — | — |
| 1979 | 86° | 55° | 71° | — | — |
| 1978 | 89° | 58° | 73° | — | — |
| 1977 | 91° | 64° | 78° | — | — |
| 1976 | 88° | 53° | 70° | — | — |
| 1975coldest | 80° | 50° | 65° | — | — |
| 1974 | 84° | 51° | 68° | — | — |
| 1973 | 91° | 64° | 78° | — | — |
| 1972 | 98° | 55° | 77° | — | — |
| 1971 | 86° | 56° | 71° | — | — |
42 years of data from ONTARIO INTL AP