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Weather & Climate in Affton, MO
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Affton enjoys a temperate climate with an average annual temperature of 58°F (15°C). Winters average 38°F in January while summers reach 78°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 45.6 inches. The area receives 7.6 inches of snow annually. Air quality is rated Good with a median AQI of 41. The city sits at an elevation of 620 feet.
Temperature
38°F Jan (3°C)
78°F Jul (26°C)
| Annual Average | 58.2°F |
| 8% above US avg | |
| January Average | 38°F (3°C) |
| July Average | 78°F (26°C) |
| Sunny Days | 293 days/yr |
Geography
| Elevation | 620 ft (189 m) |
| Area | 4.6 sq mi (11.9 km²) |
| Population Density | 4,384/sq mi |
| Coordinates | 38.5506°N, 90.3332°W |
| Timezone | America/Chicago |
| Nearest Airport | St Louis Lambert International (STL) 14 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 41.0 |
| Rating | Good |
Earthquake History
43 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 | 72 km | 21 km |
| Mar 2, 1990 | 9 km NW of Vernon, Illinois | M3.4 | 106 km | 0 km |
| Aug 27, 1993 | 5 km SSE of Olympian Village, Missouri | M3.3 | 52 km | 22 km |
| Jan 29, 1993 | 7 km WNW of Brownstown, Illinois | M3.2 | 125 km | 5 km |
| Oct 24, 1990 | 5 km ENE of Woodlawn, Illinois | M3.2 | 121 km | 1 km |
| Dec 27, 1992 | 2 km E of Pocahontas, Missouri | M3.2 | 133 km | 10 km |
| Apr 6, 1994 | 2 km NE of Tamaroa, Illinois | M3.2 | 107 km | 15 km |
| Jul 1, 2017 | 9 km SSE of Mulberry Grove, Illinois | M3.1 | 102 km | 17 km |
| Mar 12, 2002 | 6 km S of Marble Hill, Missouri | M3.1 | 148 km | 10 km |
| Jan 23, 1991 | 3 km WSW of Logan, Illinois | M3.1 | 145 km | 1 km |
| Jun 27, 2005 | 6 km E of Grand Tower, Illinois | M3.0 | 130 km | 10 km |
| Feb 28, 1994 | 5 km NW of Harrison, Illinois | M3.0 | 116 km | 5 km |
| May 18, 2006 | 9 km SSE of De Soto, Missouri | M2.9 | 58 km | 6 km |
| Sep 5, 1995 | 3 km N of Woodlawn, Illinois | M2.9 | 115 km | 4 km |
| Sep 5, 2004 | 3 km WNW of Saint Peter, Illinois | M2.9 | 131 km | 33 km |
| Jul 8, 2003 | 1 km N of Leasburg, Missouri | M2.9 | 97 km | 4 km |
| Apr 29, 2022 | 1 km SSW of Peerless Park, Missouri | M2.8 | 15 km | 8 km |
| Mar 28, 2024 | 1 km NNE of Germantown, Illinois | M2.8 | 70 km | 24 km |
| Aug 26, 1992 | 5 km W of Frohna, Missouri | M2.8 | 116 km | 2 km |
| Sep 13, 1997 | 3 km SSE of Darmstadt, Illinois | M2.8 | 62 km | 16 km |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Tornado History
576 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF4. Total: 70 fatalities, 1,162 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Feb 28, 2017 | EF4 | 96 km | 53.5 mi | 1 |
| Nov 17, 2013 | EF4 | 78 km | 10.6 mi | 2 |
| Apr 22, 2011 | EF4 | 25 km | 21.3 mi | 0 |
| Apr 3, 1981 | EF4 | 26 km | 11.9 mi | 0 |
| Jun 22, 1969 | EF4 | 95 km | 20.2 mi | 2 |
| Jun 22, 1969 | EF4 | 93 km | 15.1 mi | 4 |
| Jan 24, 1967 | EF4 | 24 km | 25.0 mi | 3 |
| Feb 10, 1959 | EF4 | 23 km | 23.9 mi | 21 |
| Feb 24, 1956 | EF4 | 52 km | 77.6 mi | 6 |
| Dec 10, 2021 | EF3 | 50 km | 24.8 mi | 1 |
| Dec 10, 2021 | EF3 | 33 km | 4.2 mi | 6 |
| Oct 24, 2021 | EF3 | 94 km | 16.7 mi | 0 |
| May 31, 2013 | EF3 | 32 km | 10.6 mi | 0 |
| May 31, 2013 | EF3 | 39 km | 31.7 mi | 0 |
| Dec 31, 2010 | EF3 | 14 km | 6.7 mi | 1 |
| Mar 13, 2006 | EF3 | 92 km | 6.0 mi | 0 |
| Mar 11, 2006 | EF3 | 48 km | 5.1 mi | 0 |
| Mar 11, 2006 | EF3 | 86 km | 53.5 mi | 2 |
| Apr 19, 1996 | EF3 | 100 km | 11.5 mi | 0 |
| Nov 15, 1988 | EF3 | 42 km | 1.0 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Wildfire History
15 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 | 88 km |
| 2019 | UNNAMED | 2,688 | 91 km |
| 2004 | CICERO CREEK | 1,846 | 83 km |
| 2021 | BERRYMAN BLOCK B AND C | 1,728 | 93 km |
| 2024 | HARMON SPRING RX | 1,330 | 89 km |
| 2018 | UNNAMED | 1,285 | 89 km |
| 2024 | RENAULT | 1,085 | 91 km |
| 2024 | FLATWOODS RX | 796 | 88 km |
| 2022 | NORTH KOFFER HOLLOW | 783 | 93 km |
| 2005 | UNNAMED | 741 | 85 km |
| 1995 | UNNAMED | 724 | 85 km |
| 1989 | UNNAMED | 600 | 83 km |
| 2024 | PIGEON ROOST | 583 | 91 km |
| 2000 | UNNAMED | 549 | 83 km |
| 1997 | FLATWOODS | 530 | 88 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 38°F (3°C) | 2.0 in | Driest |
| February | 35°F (2°C) | 2.2 in | |
| March | 45°F (7°C) | 3.5 in | |
| April | 56°F (13°C) | 3.7 in | |
| May | 66°F (19°C) | 4.1 in | Wettest |
| June | 75°F (24°C) | 3.6 in | |
| July | 78°F (26°C) | 3.7 in | Warmest |
| August | 77°F (25°C) | 3.2 in | |
| September | 70°F (21°C) | 3.3 in | |
| October | 58°F (15°C) | 2.8 in | |
| November | 46°F (8°C) | 3.5 in | |
| December | 34°F (1°C) | 3.0 in | Coldest |
Affton has a seasonal temperature swing of 44°F / from 34°F in December to 78°F in July. Total annual precipitation is 38.6 inches, with May being the wettest month (4.1") and January the driest (2.0").