Weather on August 21
Rialto, CA
55 Years of Data
Avg High
93°F
Avg Low
64°F
Warmest
1982
94°F avg
Coldest
2002
70°F avg
About This Date
August 21st in Rialto, CA typically brings hot summer weather, with average highs around 93°F and lows near 64°F — a 29°F daily swing. Over 48 years of records, the warmest August 21st was in 1982 (94°F average), while the coldest was 2002 (70°F) — a 24°F range across recorded history. This date has historically been dry, with little recorded precipitation.
Planning for August 21st in Rialto, CA? Stay hydrated and seek shade during peak afternoon hours.
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025 | 106° | 70° | 88° | — | — |
| 2017 | 87° | 58° | 72° | — | — |
| 2016 | 88° | 68° | 78° | — | — |
| 2015 | 85° | 62° | 73° | — | — |
| 2014 | 87° | 61° | 74° | — | — |
| 2013 | 98° | 68° | 83° | — | — |
| 2012 | 90° | 68° | 79° | — | — |
| 2011 | 85° | 57° | 71° | — | — |
| 2010 | 94° | 68° | 81° | — | — |
| 2009 | 88° | 67° | 77° | — | — |
| 2008 | 89° | 63° | 76° | — | — |
| 2007 | 97° | 68° | 82° | — | — |
| 2006 | 95° | 63° | 79° | — | — |
| 2005 | 100° | 65° | 82° | — | — |
| 2004 | 85° | 58° | 71° | — | — |
| 2003 | 90° | 64° | 77° | — | — |
| 2002coldest | 82° | 57° | 70° | — | — |
| 2001 | 86° | 56° | 71° | — | — |
| 2000 | 92° | 59° | 75° | — | — |
| 1999 | 101° | 69° | 85° | — | — |
| 1998 | 99° | 67° | 83° | — | — |
| 1997 | 97° | 68° | 82° | — | — |
| 1996 | 100° | 64° | 82° | — | — |
| 1995 | 95° | 71° | 83° | — | — |
| 1994 | 94° | 64° | 79° | — | — |
| 1993 | 92° | 61° | 76° | — | — |
| 1992 | 95° | 66° | 81° | — | — |
| 1991 | 97° | 69° | 83° | — | — |
| 1990 | 87° | 57° | 72° | — | — |
| 1989 | 82° | 60° | 71° | — | — |
| 1988 | 88° | 60° | 74° | — | — |
| 1987 | 92° | 60° | 76° | — | — |
| 1986 | 100° | 71° | 86° | — | — |
| 1985 | 95° | 55° | 75° | — | — |
| 1984 | 94° | 71° | 82° | — | — |
| 1983 | 83° | 64° | 73° | — | — |
| 1982warmest | 109° | 78° | 94° | — | — |
| 1981 | 107° | 63° | 85° | — | — |
| 1980 | 95° | 58° | 76° | — | — |
| 1979 | 90° | 63° | 76° | — | — |
| 1978 | 88° | 68° | 78° | — | — |
| 1977 | 94° | 67° | 80° | — | — |
| 1976 | 94° | 59° | 76° | — | — |
| 1975 | 86° | 57° | 72° | — | — |
| 1974 | 98° | 58° | 78° | — | — |
| 1973 | 96° | 68° | 82° | — | — |
| 1972 | 101° | 59° | 80° | — | — |
| 1971 | 93° | 62° | 78° | — | — |
48 years of data from FONTANA 5 N