August weather in O'Fallon, IL
The average temperature in O'Fallon in August is 77.2°F (65.3°F–89.1°F). Average precipitation: 3.92 inches.
August is a summer month in O'Fallon, and is warmer than the annual average of 57.7°F. Daily temperatures swing about 23.8°F between overnight low and afternoon high. Expect about 7 days with precipitation. Daylight averages about 13h 30m. For travel, August is hot.
Avg High
89.1°F
Avg Low
65.3°F
Precipitation
3.92 in
Daylight
13h 30m
August records in O'Fallon
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| August 1 | 100.0°F (1980) | 50.0°F (1971) | 2.85 in (1968) |
| August 2 | 100.0°F (1964) | 53.1°F (1977) | 1.82 in (1966) |
| August 3 | 104.0°F (1964) | 51.1°F (1965) | 1.25 in (1967) |
| August 4 | 100.9°F (1954) | 48.9°F (1976) | 2.01 in (1962) |
| August 5 | 100.0°F (1956) | 52.0°F (1974) | 1.41 in (1998) |
| August 6 | 99.0°F (1983) | 50.0°F (1997) | 1.93 in (2002) |
| August 7 | 100.0°F (2007) | 46.0°F (1990) | 1.97 in (2018) |
| August 8 | 100.9°F (2007) | 46.0°F (1989) | 1.10 in (2014) |
| August 9 | 100.9°F (2007) | 46.0°F (1989) | 3.00 in (1991) |
| August 10 | 100.0°F (1980) | 46.0°F (1989) | 3.51 in (1961) |
| August 11 | 100.0°F (2005) | 46.9°F (1989) | 1.44 in (1958) |
| August 12 | 100.9°F (2007) | 45.0°F (1967) | 4.00 in (2020) |
| August 13 | 100.9°F (2007) | 46.0°F (1964) | 2.61 in (1974) |
| August 14 | 100.0°F (2007) | 46.0°F (2004) | 2.33 in (2010) |
| August 15 | 105.1°F (2007) | 46.0°F (2004) | 2.71 in (2016) |
| August 16 | 105.1°F (2007) | 48.0°F (2004) | 2.27 in (1957) |
| August 17 | 100.0°F (1988) | 52.0°F (1994) | 2.44 in (1959) |
| August 18 | 100.9°F (1954) | 50.0°F (1989) | 2.00 in (1984) |
| August 19 | 102.9°F (1962) | 51.1°F (1977) | 1.00 in (1997) |
| August 20 | 102.9°F (1962) | 48.0°F (1967) | 0.98 in (2011) |
| August 21 | 100.9°F (2003) | 46.0°F (1967) | 1.60 in (2010) |
| August 22 | 100.0°F (2003) | 46.9°F (2024) | 1.31 in (2019) |
| August 23 | 100.0°F (2007) | 51.1°F (1997) | 2.23 in (1977) |
| August 24 | 100.0°F (2007) | 50.0°F (1966) | 2.15 in (1996) |
| August 25 | 98.1°F (2011) | 50.0°F (1966) | 0.66 in (1978) |
| August 26 | 99.0°F (1983) | 50.0°F (1970) | 1.69 in (2004) |
| August 27 | 99.0°F (1983) | 48.9°F (1967) | 2.60 in (1987) |
| August 28 | 100.0°F (1990) | 43.0°F (1967) | 0.70 in (1950) |
| August 29 | 99.0°F (1990) | 39.0°F (1986) | 2.20 in (2004) |
| August 30 | 98.1°F (1951) | 41.0°F (1986) | 1.20 in (1978) |
| August 31 | 99.0°F (1951) | 44.1°F (1988) | 3.30 in (1962) |