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Weather & Climate in O'Fallon, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
O'Fallon enjoys a temperate climate with an average annual temperature of 58°F (14°C). Winters average 34°F in January while summers reach 79°F in July. The area gets 293 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 43.4 inches. The area receives 11.2 inches of snow annually. Air quality is rated Good with a median AQI of 43. The city sits at an elevation of 535 feet.
Temperature
34°F Jan (1°C)
79°F Jul (26°C)
| Annual Average | 57.7°F |
| 7% above US avg | |
| January Average | 34°F (1°C) |
| July Average | 79°F (26°C) |
| Sunny Days | 293 days/yr |
Geography
| Elevation | 535 ft (163 m) |
| Area | 14.5 sq mi (37.5 km²) |
| Population Density | 2,033/sq mi |
| Coordinates | 38.6000°N, 89.9154°W |
| Timezone | America/Chicago |
| County | St. Clair County County |
| Nearest Airport | St Louis Regional (ALN) 21 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively High |
| Risk Score | 94.9 / 100 |
| Social Vulnerability | 37.9 / 100 |
| Community Resilience | 74.9 / 100 |
Hazard Breakdown
| Tornado | Relatively High |
| Hurricane | Very Low |
| Earthquake | Relatively Moderate |
| Wildfire | Very Low |
| Flood | Relatively High |
| Hail | Relatively High |
| Strong Wind | Relatively Moderate |
| Heat Wave | Relatively High |
| Winter Weather | Relatively High |
| Lightning | Relatively High |
| Ice Storm | Relatively High |
| Drought | Relatively Low |
| Cold Wave | Relatively High |
| Landslide | Relatively Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
48 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 | 104 km | 21 km |
| Mar 2, 1990 | 9 km NW of Vernon, Illinois | M3.4 | 70 km | 0 km |
| May 30, 2015 | 4 km ENE of Geff, Illinois | M3.4 | 137 km | 26 km |
| Aug 27, 1993 | 5 km SSE of Olympian Village, Missouri | M3.3 | 73 km | 22 km |
| Oct 24, 1990 | 5 km ENE of Woodlawn, Illinois | M3.2 | 87 km | 1 km |
| Jan 29, 1993 | 7 km WNW of Brownstown, Illinois | M3.2 | 91 km | 5 km |
| May 2, 2003 | 10 km ENE of Thompsonville, Illinois | M3.2 | 130 km | 0 km |
| Dec 27, 1992 | 2 km E of Pocahontas, Missouri | M3.2 | 125 km | 10 km |
| Apr 6, 1994 | 2 km NE of Tamaroa, Illinois | M3.2 | 79 km | 15 km |
| Jul 1, 2017 | 9 km SSE of Mulberry Grove, Illinois | M3.1 | 66 km | 17 km |
| Jan 23, 1991 | 3 km WSW of Logan, Illinois | M3.1 | 117 km | 1 km |
| Jun 27, 2005 | 6 km E of Grand Tower, Illinois | M3.0 | 116 km | 10 km |
| Mar 1, 2006 | 2 km N of Buncombe, Illinois | M3.0 | 147 km | 6 km |
| Feb 28, 1994 | 5 km NW of Harrison, Illinois | M3.0 | 98 km | 5 km |
| May 18, 2006 | 9 km SSE of De Soto, Missouri | M2.9 | 81 km | 6 km |
| Sep 5, 2004 | 3 km WNW of Saint Peter, Illinois | M2.9 | 94 km | 33 km |
| Sep 5, 1995 | 3 km N of Woodlawn, Illinois | M2.9 | 81 km | 4 km |
| Jul 8, 2003 | 1 km N of Leasburg, Missouri | M2.9 | 132 km | 4 km |
| Apr 29, 2022 | 1 km SSW of Peerless Park, Missouri | M2.8 | 51 km | 8 km |
| Mar 28, 2024 | 1 km NNE of Germantown, Illinois | M2.8 | 33 km | 24 km |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Tornado History
616 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF5. Total: 66 fatalities, 1,159 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Dec 18, 1957 | EF5 | 82 km | 5.4 mi | 1 |
| Feb 28, 2017 | EF4 | 98 km | 53.5 mi | 1 |
| Nov 17, 2013 | EF4 | 45 km | 10.6 mi | 2 |
| Apr 22, 2011 | EF4 | 52 km | 21.3 mi | 0 |
| Apr 3, 1981 | EF4 | 23 km | 11.9 mi | 0 |
| Jan 24, 1967 | EF4 | 56 km | 25.0 mi | 3 |
| Feb 10, 1959 | EF4 | 60 km | 23.9 mi | 21 |
| Dec 18, 1957 | EF4 | 81 km | 16.8 mi | 1 |
| Feb 24, 1956 | EF4 | 89 km | 77.6 mi | 6 |
| Dec 10, 2021 | EF3 | 86 km | 24.8 mi | 1 |
| Dec 10, 2021 | EF3 | 21 km | 4.2 mi | 6 |
| May 31, 2013 | EF3 | 30 km | 10.6 mi | 0 |
| May 31, 2013 | EF3 | 73 km | 31.7 mi | 0 |
| Apr 19, 2011 | EF3 | 94 km | 4.3 mi | 0 |
| Dec 31, 2010 | EF3 | 50 km | 6.7 mi | 1 |
| Mar 11, 2006 | EF3 | 87 km | 53.5 mi | 2 |
| Mar 11, 2006 | EF3 | 65 km | 5.1 mi | 0 |
| Jun 1, 1999 | EF3 | 83 km | 10.0 mi | 1 |
| Apr 19, 1996 | EF3 | 97 km | 11.5 mi | 0 |
| Nov 15, 1988 | EF3 | 72 km | 1.0 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Wildfire History
6 wildfires (100+ acres) recorded within 100 km. Largest: KINKAID RX (1,215 acres, 2019).
| Year | Name | Acres Burned | Distance |
| 2019 | KINKAID RX | 1,215 | 97 km |
| 2022 | KINKAID STATE FISH AND WILDLIFE AREA RX | 1,115 | 97 km |
| 2021 | STATE OF ILLINOIS TRACT RX | 1,011 | 88 km |
| 2018 | UNNAMED | 729 | 95 km |
| 2020 | UNNAMED | 687 | 95 km |
| 2022 | BLOWDOWN 16 RX | 553 | 99 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 34°F (1°C) | 2.1 in | Coldest, Driest |
| February | 34°F (1°C) | 2.3 in | |
| March | 44°F (7°C) | 3.4 in | |
| April | 55°F (13°C) | 3.7 in | |
| May | 65°F (18°C) | 4.1 in | Wettest |
| June | 74°F (23°C) | 3.7 in | |
| July | 79°F (26°C) | 3.7 in | Warmest |
| August | 76°F (24°C) | 3.2 in | |
| September | 69°F (20°C) | 3.3 in | |
| October | 57°F (14°C) | 2.7 in | |
| November | 45°F (7°C) | 3.1 in | |
| December | 34°F (1°C) | 2.9 in |
O'Fallon has a seasonal temperature swing of 45°F / from 34°F in January to 79°F in July. Total annual precipitation is 38.1 inches, with May being the wettest month (4.1") and January the driest (2.1").