Weather on August 21
Ontario, CA
55 Years of Data
About This Date
August 21st in Ontario, 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 Ontario, CA? Stay hydrated and seek shade during peak afternoon hours.
| 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° | — | — |
Ontario, CA Temperature Range by Month
Average monthly highs and lows. The shaded band shows the typical daily temperature range.
Ontario, CA Monthly Precipitation
Average rainfall per month, in inches.
Ontario, CA Daily Temperature Calendar
Average daily high temperature for every day of the year. Each cell is the climatological mean for that calendar day across 55 years of NOAA data.
Best Time to Visit Ontario, CA
Ontario, CA has no months that meet our "pleasant" threshold — every season has tradeoffs.