Weather on May 21
Ontario, CA
55 Years of Data
Avg High
78°F
Avg Low
54°F
Warmest
2000
81°F avg
Coldest
1972
53°F avg
About This Date
May 21st in Ontario, CA typically brings pleasant spring weather, with average highs around 78°F and lows near 54°F. Over 42 years of records, the warmest May 21st was in 2000 (81°F average), while the coldest was 1972 (53°F) — a 28°F range across recorded history. Rain or other precipitation has occurred on about 2% of May 21st dates historically. The last decade has been 1.4°F cooler on this date compared to 20-30 years ago.
The last decade has been 1.4°F cooler on this date compared to 20-30 years ago.
Planning for May 21st in Ontario, CA? Great weather for outdoor activities.
Warming Trend
1.7°F per decade on this date
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025 | 95° | 63° | 79° | — | — |
| 2024 | 76° | 55° | 65° | — | — |
| 2023 | 84° | 60° | 72° | — | — |
| 2022 | 74° | 57° | 65° | — | — |
| 2021 | 76° | 52° | 64° | — | — |
| 2020 | 89° | 58° | 73° | — | — |
| 2019 | 66° | 56° | 61° | — | — |
| 2018 | 67° | 57° | 62° | — | — |
| 2017 | 96° | 62° | 79° | — | — |
| 2016 | 70° | 51° | 60° | — | — |
| 2015 | 69° | 57° | 63° | — | — |
| 2014 | 73° | 53° | 63° | — | — |
| 2013 | 88° | 60° | 74° | — | — |
| 2012 | 94° | 60° | 77° | — | — |
| 2011 | 80° | 53° | 67° | — | — |
| 2010 | 77° | 55° | 66° | — | — |
| 2009 | 85° | 57° | 71° | — | — |
| 2008 | 74° | 59° | 66° | — | — |
| 2007 | 64° | 56° | 60° | — | — |
| 2006 | 69° | 59° | 64° | — | — |
| 2005 | 95° | 62° | 79° | — | — |
| 2004 | 70° | 57° | 63° | — | — |
| 2003 | 100° | 63° | 81° | — | — |
| 2002 | 68° | 47° | 57° | — | — |
| 2001 | 82° | 58° | 70° | — | — |
| 2000warmest | 101° | 61° | 81° | — | — |
| 1999 | 70° | 54° | 62° | — | — |
| 1998 | 72° | 52° | 62° | — | — |
| 1984 | 85° | 52° | 68° | — | — |
| 1983 | 86° | 51° | 69° | — | — |
| 1982 | 75° | 57° | 66° | — | — |
| 1981 | 76° | 42° | 59° | — | — |
| 1980 | 63° | 52° | 57° | 0.13" | — |
| 1979 | 72° | 54° | 63° | — | — |
| 1978 | 79° | 48° | 63° | — | — |
| 1977 | 82° | 50° | 66° | — | — |
| 1976 | 75° | 47° | 61° | — | — |
| 1975 | 65° | 41° | 53° | — | — |
| 1974 | 86° | 44° | 65° | — | — |
| 1973 | 73° | 55° | 64° | — | — |
| 1972coldest | 69° | 38° | 53° | — | — |
| 1971 | 71° | 49° | 60° | — | — |
42 years of data from ONTARIO INTL AP