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Weather & Climate in Thomson, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Thomson experiences four distinct seasons with an average annual temperature of 50°F (10°C). Winters average 21°F in January while summers reach 75°F in July. The area gets 275 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 34.3 inches. Air quality is rated Good with a median AQI of 43. The city sits at an elevation of 605 feet.
Temperature
21°F Jan (-6°C)
75°F Jul (24°C)
| Annual Average | 49.9°F |
| 8% below US avg | |
| January Average | 21°F (-6°C) |
| July Average | 75°F (24°C) |
| Sunny Days | 275 days/yr |
Geography
| Elevation | 605 ft (184 m) |
| Area | 2.2 sq mi (5.7 km²) |
| Population Density | 687/sq mi |
| Coordinates | 41.9747°N, 90.1122°W |
| Timezone | America/Chicago |
| County | Clinton County County |
| Nearest Airport | Quad Cities International (MLI) 42 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively Low |
| Risk Score | 64.8 / 100 |
| Social Vulnerability | 34.6 / 100 |
| Community Resilience | 87.5 / 100 |
Hazard Breakdown
| Tornado | Relatively Moderate |
| Hurricane | Very Low |
| Earthquake | Very Low |
| Wildfire | Very Low |
| Flood | Relatively Low |
| Hail | Relatively Moderate |
| Strong Wind | Relatively High |
| Heat Wave | Relatively Low |
| Winter Weather | Relatively Low |
| Lightning | Relatively Low |
| Ice Storm | Relatively Moderate |
| Drought | Relatively High |
| Cold Wave | Relatively Moderate |
| Landslide | Relatively Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
6 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M4.2.
| Jun 28, 2004 | 12 km NW of Dayton, Illinois | M4.2 | 116 km | 10 km |
| Feb 10, 2010 | 2 km NW of Lily Lake, Illinois | M3.8 | 133 km | 10 km |
| Sep 2, 1999 | 8 km W of Amboy, Illinois | M3.5 | 63 km | 5 km |
| Jul 15, 2024 | 2 km WNW of Somonauk, Illinois | M3.1 | 122 km | 10 km |
| Mar 25, 2015 | 3 km WNW of Lake in the Hills, Illinois | M2.9 | 146 km | 6 km |
| Jun 10, 2013 | 4 km NNE of Virgil, Illinois | M2.6 | 133 km | 5 km |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Tornado History
612 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF4. Total: 8 fatalities, 221 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Apr 9, 2015 | EF4 | 69 km | 30.1 mi | 2 |
| Mar 29, 1981 | EF4 | 35 km | 5.1 mi | 0 |
| Apr 11, 1965 | EF4 | 69 km | 91.5 mi | 1 |
| May 9, 1995 | EF3 | 77 km | 10.0 mi | 0 |
| May 9, 1995 | EF3 | 79 km | 22.0 mi | 0 |
| Jun 19, 1993 | EF3 | 63 km | 14.0 mi | 0 |
| Jul 13, 1992 | EF3 | 87 km | 5.0 mi | 0 |
| Mar 13, 1990 | EF3 | 44 km | 15.5 mi | 0 |
| May 8, 1988 | EF3 | 61 km | 32.0 mi | 0 |
| May 8, 1988 | EF3 | 68 km | 16.0 mi | 0 |
| Aug 5, 1979 | EF3 | 44 km | 5.7 mi | 0 |
| Aug 15, 1978 | EF3 | 96 km | 6.4 mi | 0 |
| Mar 4, 1976 | EF3 | 97 km | 0.8 mi | 0 |
| Jun 20, 1974 | EF3 | 13 km | 10.6 mi | 1 |
| Jun 14, 1974 | EF3 | 81 km | 48.6 mi | 0 |
| May 13, 1974 | EF3 | 57 km | 3.6 mi | 0 |
| Sep 9, 1970 | EF3 | 74 km | 4.7 mi | 0 |
| Apr 16, 1967 | EF3 | 63 km | 27.8 mi | 0 |
| Jan 24, 1967 | EF3 | 93 km | 24.9 mi | 0 |
| Jan 24, 1967 | EF3 | 11 km | 7.4 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Wildfire History
1 wildfire (100+ acres) recorded within 100 km. Largest: COLD SPRINGS (552 acres, 2009).
| Year | Name | Acres Burned | Distance |
| 2009 | COLD SPRINGS | 552 | 87 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 21°F (-6°C) | 1.4 in | Coldest |
| February | 24°F (-4°C) | 1.4 in | Driest |
| March | 36°F (2°C) | 2.6 in | |
| April | 49°F (9°C) | 3.6 in | |
| May | 60°F (16°C) | 4.3 in | |
| June | 69°F (21°C) | 4.6 in | Wettest |
| July | 75°F (24°C) | 3.7 in | Warmest |
| August | 71°F (22°C) | 4.5 in | |
| September | 63°F (17°C) | 3.5 in | |
| October | 52°F (11°C) | 2.7 in | |
| November | 38°F (3°C) | 2.6 in | |
| December | 25°F (-4°C) | 2.0 in |
Thomson has a seasonal temperature swing of 53°F / from 21°F in January to 75°F in July. Total annual precipitation is 36.9 inches, with June being the wettest month (4.6") and February the driest (1.4").