Weather on September 21
Rancho Cucamonga, CA
55 Years of Data
Avg High
88°F
Avg Low
60°F
Warmest
2021
85°F avg
Coldest
1976
64°F avg
About This Date
September 21st in Rancho Cucamonga, CA typically brings warm fall weather, with average highs around 88°F and lows near 60°F — a 28°F daily swing. Over 41 years of records, the warmest September 21st was in 2021 (85°F average), while the coldest was 1976 (64°F) — a 21°F range across recorded history. This date has historically been dry, with little recorded precipitation. Temperatures on this date have remained relatively stable over the past several decades.
Temperatures on this date have remained relatively stable over the past several decades.
Planning for September 21st in Rancho Cucamonga, CA? Stay hydrated and seek shade during peak afternoon hours.
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025 | 82° | 65° | 73° | — | — |
| 2024 | 79° | 58° | 68° | — | — |
| 2023 | 76° | 60° | 68° | — | — |
| 2022 | 85° | 60° | 72° | — | — |
| 2021warmest | 103° | 67° | 85° | — | — |
| 2020 | 93° | 63° | 78° | — | — |
| 2019 | 94° | 62° | 78° | — | — |
| 2018 | 92° | 62° | 77° | — | — |
| 2017 | 71° | 57° | 64° | — | — |
| 2016 | 88° | 68° | 78° | — | — |
| 2015 | 88° | 71° | 79° | — | — |
| 2014 | 84° | 64° | 74° | — | — |
| 2013 | 80° | 62° | 71° | — | — |
| 2012 | 102° | 67° | 84° | — | — |
| 2011 | 90° | 59° | 74° | — | — |
| 2010 | 76° | 58° | 67° | — | — |
| 2009 | 93° | 63° | 78° | — | — |
| 2008 | 81° | 57° | 69° | — | — |
| 2007 | 79° | 53° | 66° | — | — |
| 2006 | 84° | 58° | 71° | — | — |
| 2005 | 88° | 60° | 74° | — | — |
| 2004 | 87° | 57° | 72° | — | — |
| 2003 | 105° | 61° | 83° | — | — |
| 2002 | 96° | 61° | 78° | — | — |
| 2001 | 91° | 58° | 74° | — | — |
| 2000 | 71° | 63° | 67° | — | — |
| 1999 | 95° | 62° | 79° | — | — |
| 1998 | 71° | 62° | 67° | — | — |
| 1983 | 94° | 67° | 80° | — | — |
| 1982 | 97° | 54° | 75° | — | — |
| 1981 | 93° | 57° | 75° | — | — |
| 1980 | 81° | 61° | 71° | — | — |
| 1979 | 93° | 59° | 76° | — | — |
| 1978 | 91° | 54° | 72° | — | — |
| 1977 | 87° | 50° | 69° | — | — |
| 1976coldest | 77° | 50° | 64° | — | — |
| 1975 | 95° | 59° | 77° | — | — |
| 1974 | 101° | 63° | 82° | — | — |
| 1973 | 80° | 51° | 66° | — | — |
| 1972 | 98° | 56° | 77° | — | — |
| 1971 | 77° | 58° | 67° | — | — |
41 years of data from ONTARIO INTL AP