All Countries
Weather & Climate in O'Fallon, MO
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
O'Fallon experiences four distinct seasons with an average annual temperature of 55°F (13°C). Winters average 29°F in January while summers reach 78°F in July. The area gets 267 sunny days per year, well above the U.S. average of 205 / making it one of the sunnier locations in the country. Annual precipitation totals 37.8 inches. The area receives 6.5 inches of snow annually. Air quality is rated Good with a median AQI of 41. The city sits at an elevation of 548 feet.
Temperature
29°F Jan (-2°C)
78°F Jul (26°C)
| Annual Average | 54.7°F |
| 1% above US avg | |
| January Average | 29°F (-2°C) |
| July Average | 78°F (26°C) |
| Sunny Days | 267 days/yr |
Geography
| Elevation | 548 ft (167 m) |
| Area | 30.6 sq mi (79.1 km²) |
| Population Density | 3,034/sq mi |
| Coordinates | 38.8106°N, 90.6999°W |
| Timezone | America/Chicago |
| Nearest Airport | St Louis Lambert International (STL) 18 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 41.0 |
| Rating | Good |
Earthquake History
28 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M3.9.
| Jun 7, 2011 | 18 km NNW of Potosi, Missouri | M3.9 | 83 km | 21 km |
| Mar 2, 1990 | 9 km NW of Vernon, Illinois | M3.4 | 133 km | 0 km |
| Aug 27, 1993 | 5 km SSE of Olympian Village, Missouri | M3.3 | 83 km | 22 km |
| Jan 29, 1993 | 7 km WNW of Brownstown, Illinois | M3.2 | 147 km | 5 km |
| Apr 6, 1994 | 2 km NE of Tamaroa, Illinois | M3.2 | 148 km | 15 km |
| Jul 1, 2017 | 9 km SSE of Mulberry Grove, Illinois | M3.1 | 128 km | 17 km |
| Jul 8, 2003 | 1 km N of Leasburg, Missouri | M2.9 | 94 km | 4 km |
| Feb 8, 2004 | 6 km SSW of Stoutsville, Missouri | M2.9 | 127 km | 5 km |
| May 18, 2006 | 9 km SSE of De Soto, Missouri | M2.9 | 86 km | 6 km |
| Apr 29, 2022 | 1 km SSW of Peerless Park, Missouri | M2.8 | 36 km | 8 km |
| Mar 28, 2024 | 1 km NNE of Germantown, Illinois | M2.8 | 105 km | 24 km |
| Jul 31, 1995 | 8 km SSW of Caledonia, Missouri | M2.8 | 125 km | 5 km |
| May 5, 2008 | 3 km SSE of Fenton, Missouri | M2.8 | 44 km | 19 km |
| Sep 13, 1997 | 3 km SSE of Darmstadt, Illinois | M2.8 | 104 km | 16 km |
| Jul 15, 1990 | 7 km SW of Potosi, Missouri | M2.7 | 104 km | 3 km |
| Nov 12, 1996 | 15 km SSE of Olympian Village, Missouri | M2.7 | 94 km | 5 km |
| Jul 22, 1998 | 12 km NE of Mine La Motte, Missouri | M2.7 | 133 km | 11 km |
| Sep 5, 2015 | 5 km SE of High Ridge, Missouri | M2.7 | 46 km | 8 km |
| Nov 25, 2013 | 8 km NE of Bonne Terre, Missouri | M2.6 | 95 km | 12 km |
| Mar 7, 2009 | 7 km S of Miramiguoa Park, Missouri | M2.6 | 78 km | 7 km |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Tornado History
532 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF4. Total: 57 fatalities, 1,037 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Apr 22, 2011 | EF4 | 20 km | 21.3 mi | 0 |
| Apr 3, 1981 | EF4 | 50 km | 11.9 mi | 0 |
| Jan 24, 1967 | EF4 | 20 km | 25.0 mi | 3 |
| Feb 10, 1959 | EF4 | 32 km | 23.9 mi | 21 |
| Feb 24, 1956 | EF4 | 44 km | 77.6 mi | 6 |
| Dec 10, 2021 | EF3 | 56 km | 4.2 mi | 6 |
| Dec 10, 2021 | EF3 | 30 km | 24.8 mi | 1 |
| May 31, 2013 | EF3 | 48 km | 10.6 mi | 0 |
| May 31, 2013 | EF3 | 14 km | 31.7 mi | 0 |
| Dec 31, 2010 | EF3 | 41 km | 6.7 mi | 1 |
| Mar 13, 2006 | EF3 | 64 km | 44.5 mi | 0 |
| Mar 13, 2006 | EF3 | 54 km | 6.0 mi | 0 |
| Mar 11, 2006 | EF3 | 83 km | 5.1 mi | 0 |
| Nov 15, 1988 | EF3 | 1 km | 1.0 mi | 0 |
| Nov 15, 1988 | EF3 | 64 km | 9.0 mi | 0 |
| Apr 29, 1984 | EF3 | 25 km | 8.0 mi | 0 |
| May 1, 1983 | EF3 | 66 km | 4.0 mi | 0 |
| May 1, 1983 | EF3 | 52 km | 16.0 mi | 0 |
| Dec 2, 1982 | EF3 | 93 km | 10.5 mi | 2 |
| Apr 22, 1981 | EF3 | 72 km | 7.1 mi | 1 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Wildfire History
9 wildfires (100+ acres) recorded within 100 km. Largest: SMITH MILL HOLLOW (3,978 acres, 2022).
| Year | Name | Acres Burned | Distance |
| 2022 | SMITH MILL HOLLOW | 3,978 | 99 km |
| 2019 | UNNAMED | 2,688 | 99 km |
| 2004 | CICERO CREEK | 1,846 | 91 km |
| 2024 | HARMON SPRING RX | 1,330 | 97 km |
| 2018 | UNNAMED | 1,285 | 97 km |
| 2022 | NORTH KOFFER HOLLOW | 783 | 100 km |
| 1989 | UNNAMED | 600 | 98 km |
| 2000 | UNNAMED | 549 | 94 km |
| 1997 | FLATWOODS | 530 | 100 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 29°F (-2°C) | 1.8 in | Coldest, Driest |
| February | 34°F (1°C) | 2.1 in | |
| March | 44°F (7°C) | 3.4 in | |
| April | 55°F (13°C) | 3.7 in | |
| May | 64°F (18°C) | 4.3 in | Wettest |
| June | 73°F (23°C) | 3.5 in | |
| July | 78°F (26°C) | 3.9 in | Warmest |
| August | 76°F (24°C) | 3.2 in | |
| September | 68°F (20°C) | 3.2 in | |
| October | 57°F (14°C) | 3.0 in | |
| November | 45°F (7°C) | 3.2 in | |
| December | 34°F (1°C) | 2.6 in |
O'Fallon has a seasonal temperature swing of 49°F / from 29°F in January to 78°F in July. Total annual precipitation is 37.8 inches, with May being the wettest month (4.3") and January the driest (1.8").