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Weather & Climate in Thayer, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Thayer experiences four distinct seasons with an average annual temperature of 55°F (13°C). Winters average 29°F in January while summers reach 77°F in July. The area gets 302 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 38.4 inches. The area receives 16.1 inches of snow annually, a moderate snowfall amount. Air quality is rated Good with a median AQI of 43. The city sits at an elevation of 639 feet.
Temperature
29°F Jan (-2°C)
77°F Jul (25°C)
| Annual Average | 54.8°F |
| 1% above US avg | |
| January Average | 29°F (-2°C) |
| July Average | 77°F (25°C) |
| Sunny Days | 302 days/yr |
Geography
| Elevation | 639 ft (195 m) |
| Area | 0.2 sq mi (0.6 km²) |
| Population Density | 1,046/sq mi |
| Coordinates | 39.5404°N, 89.7580°W |
| Timezone | America/Chicago |
| County | Sangamon County County |
| Nearest Airport | St Louis Regional (ALN) 48 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively Moderate |
| Risk Score | 91.7 / 100 |
| Social Vulnerability | 32.0 / 100 |
| Community Resilience | 92.2 / 100 |
Hazard Breakdown
| Tornado | Relatively High |
| Hurricane | Very Low |
| Earthquake | Relatively Moderate |
| Wildfire | Very Low |
| Flood | Relatively Moderate |
| Hail | Relatively High |
| Strong Wind | Relatively High |
| Heat Wave | Relatively Moderate |
| Winter Weather | Relatively High |
| Lightning | Relatively High |
| Ice Storm | Relatively Moderate |
| Drought | Relatively High |
| Cold Wave | Relatively High |
| Landslide | Relatively Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
16 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M3.4.
| Mar 2, 1990 | 9 km NW of Vernon, Illinois | M3.4 | 92 km | 0 km |
| May 13, 2025 | 7 km SSW of Lerna, Illinois | M3.3 | 125 km | 10 km |
| Jan 29, 1993 | 7 km WNW of Brownstown, Illinois | M3.2 | 84 km | 5 km |
| Oct 24, 1990 | 5 km ENE of Woodlawn, Illinois | M3.2 | 149 km | 1 km |
| Jul 1, 2017 | 9 km SSE of Mulberry Grove, Illinois | M3.1 | 89 km | 17 km |
| Sep 5, 1995 | 3 km N of Woodlawn, Illinois | M2.9 | 145 km | 4 km |
| Sep 5, 2004 | 3 km WNW of Saint Peter, Illinois | M2.9 | 104 km | 33 km |
| Apr 24, 1990 | 5 km SW of Newton, Illinois | M2.9 | 149 km | 18 km |
| Apr 29, 2022 | 1 km SSW of Peerless Park, Missouri | M2.8 | 129 km | 8 km |
| Mar 28, 2024 | 1 km NNE of Germantown, Illinois | M2.8 | 110 km | 24 km |
| May 5, 2008 | 3 km SSE of Fenton, Missouri | M2.8 | 130 km | 19 km |
| Sep 13, 1997 | 3 km SSE of Darmstadt, Illinois | M2.8 | 139 km | 16 km |
| Sep 5, 2015 | 5 km SE of High Ridge, Missouri | M2.7 | 139 km | 8 km |
| Sep 19, 2024 | 1 km S of Old Monroe, Missouri | M2.6 | 110 km | 2 km |
| May 17, 2022 | 6 km NNW of Mount Vernon, Illinois | M2.5 | 148 km | 16 km |
| Jan 15, 1998 | 1 km SSE of Fenton, Missouri | M2.5 | 129 km | 16 km |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Tornado History
665 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF4. Total: 31 fatalities, 692 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Apr 3, 1981 | EF4 | 97 km | 11.9 mi | 0 |
| May 5, 1977 | EF4 | 90 km | 7.3 mi | 0 |
| Mar 20, 1976 | EF4 | 87 km | 63.7 mi | 0 |
| Jun 14, 1957 | EF4 | 24 km | 4.3 mi | 2 |
| Dec 10, 2021 | EF3 | 91 km | 4.2 mi | 6 |
| Dec 1, 2018 | EF3 | 34 km | 12.5 mi | 0 |
| May 31, 2013 | EF3 | 89 km | 10.6 mi | 0 |
| Apr 19, 2011 | EF3 | 12 km | 4.3 mi | 0 |
| Dec 31, 2010 | EF3 | 50 km | 3.6 mi | 0 |
| Aug 19, 2009 | EF3 | 49 km | 24.3 mi | 0 |
| Jun 1, 1999 | EF3 | 26 km | 10.0 mi | 1 |
| Apr 19, 1996 | EF3 | 58 km | 14.5 mi | 0 |
| Apr 19, 1996 | EF3 | 93 km | 9.4 mi | 0 |
| May 13, 1995 | EF3 | 99 km | 25.0 mi | 0 |
| May 9, 1995 | EF3 | 38 km | 50.0 mi | 0 |
| May 1, 1983 | EF3 | 52 km | 4.0 mi | 0 |
| Apr 7, 1980 | EF3 | 98 km | 7.3 mi | 0 |
| Jul 26, 1978 | EF3 | 29 km | 8.9 mi | 0 |
| Aug 21, 1977 | EF3 | 96 km | 26.9 mi | 6 |
| Aug 6, 1977 | EF3 | 11 km | 4.1 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 29°F (-2°C) | 1.7 in | Coldest, Driest |
| February | 31°F (-1°C) | 1.9 in | |
| March | 42°F (6°C) | 3.3 in | |
| April | 53°F (12°C) | 3.7 in | |
| May | 64°F (18°C) | 4.3 in | Wettest |
| June | 72°F (22°C) | 3.9 in | |
| July | 77°F (25°C) | 3.7 in | Warmest |
| August | 74°F (23°C) | 3.4 in | |
| September | 67°F (20°C) | 3.3 in | |
| October | 56°F (13°C) | 2.6 in | |
| November | 43°F (6°C) | 3.0 in | |
| December | 31°F (-1°C) | 2.7 in |
Thayer has a seasonal temperature swing of 49°F / from 29°F in January to 77°F in July. Total annual precipitation is 37.5 inches, with May being the wettest month (4.3") and January the driest (1.7").