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Weather & Climate in Union, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Union experiences four distinct seasons with an average annual temperature of 48°F (9°C). Winters average 21°F in January while summers reach 73°F in July. The area gets 260 sunny days per year, above the national average. Annual precipitation totals 37.6 inches. The area receives 30.8 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 857 feet.
Temperature
21°F Jan (-6°C)
73°F Jul (23°C)
| Annual Average | 48.2°F |
| 11% below US avg | |
| January Average | 21°F (-6°C) |
| July Average | 73°F (23°C) |
| Sunny Days | 260 days/yr |
Geography
| Elevation | 857 ft (261 m) |
| Area | 0.8 sq mi (2.2 km²) |
| Population Density | 896/sq mi |
| Coordinates | 42.2316°N, 88.5448°W |
| Timezone | America/Chicago |
| County | McHenry County County |
| Nearest Airport | Chicago/Rockford International (RFD) 28 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively Moderate |
| Risk Score | 90.8 / 100 |
| Social Vulnerability | 10.6 / 100 |
| Community Resilience | 84.0 / 100 |
Hazard Breakdown
| Tornado | Relatively High |
| Hurricane | Very Low |
| Earthquake | Relatively Low |
| Wildfire | Very Low |
| Flood | Relatively Moderate |
| Hail | Relatively Moderate |
| Strong Wind | Relatively High |
| Heat Wave | Relatively Low |
| Winter Weather | Relatively Moderate |
| Lightning | Relatively Moderate |
| Ice Storm | Relatively Low |
| Drought | Relatively Low |
| Cold Wave | Relatively High |
| Landslide | Very Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
8 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 | 91 km | 10 km |
| Feb 10, 2010 | 2 km NW of Lily Lake, Illinois | M3.8 | 30 km | 10 km |
| Sep 2, 1999 | 8 km W of Amboy, Illinois | M3.5 | 93 km | 5 km |
| Nov 4, 2013 | 1 km SSW of Lyons, Illinois | M3.2 | 76 km | 1 km |
| Jul 15, 2024 | 2 km WNW of Somonauk, Illinois | M3.1 | 67 km | 10 km |
| Mar 25, 2015 | 3 km WNW of Lake in the Hills, Illinois | M2.9 | 16 km | 6 km |
| Jun 10, 2013 | 4 km NNE of Virgil, Illinois | M2.6 | 27 km | 5 km |
| Mar 15, 2025 | 6 km W of Dwight, Illinois | M2.6 | 127 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: EF5. Total: 113 fatalities, 2,320 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Aug 28, 1990 | EF5 | 63 km | 16.4 mi | 29 |
| Apr 9, 2015 | EF4 | 75 km | 30.1 mi | 2 |
| Apr 27, 1984 | EF4 | 84 km | 6.5 mi | 1 |
| Jun 29, 1979 | EF4 | 83 km | 5.4 mi | 0 |
| Jun 13, 1976 | EF4 | 77 km | 3.3 mi | 2 |
| Sep 28, 1972 | EF4 | 56 km | 5.2 mi | 0 |
| Apr 21, 1967 | EF4 | 86 km | 15.0 mi | 33 |
| Apr 21, 1967 | EF4 | 24 km | 8.8 mi | 1 |
| Apr 21, 1967 | EF4 | 31 km | 25.5 mi | 24 |
| Apr 11, 1965 | EF4 | 14 km | 9.1 mi | 6 |
| Jun 20, 2021 | EF3 | 61 km | 17.6 mi | 0 |
| Jan 7, 2008 | EF3 | 40 km | 10.8 mi | 0 |
| Jan 7, 2008 | EF3 | 29 km | 13.2 mi | 0 |
| Mar 27, 1991 | EF3 | 81 km | 15.0 mi | 0 |
| Apr 27, 1984 | EF3 | 78 km | 9.0 mi | 1 |
| Aug 5, 1979 | EF3 | 89 km | 5.7 mi | 0 |
| Jun 30, 1977 | EF3 | 82 km | 6.1 mi | 0 |
| Mar 12, 1976 | EF3 | 69 km | 22.6 mi | 0 |
| Jan 24, 1967 | EF3 | 79 km | 24.9 mi | 0 |
| Jul 19, 1963 | EF3 | 46 km | 10.6 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Tsunami History
1 tsunami recorded within 500 km. Highest wave on record: 3.0 m (10 ft).
| Year | Location | Cause | Max Wave | Deaths | Distance |
| 1954 | MICHIGAN CITY, IN (LAKE MICHIGAN) | Avalanche | 3.0 m | 7 | 150 km |
Source: NOAA/NCEI Historical Tsunami Database.
Wildfire History
3 wildfires (100+ acres) recorded within 100 km. Largest: UNNAMED (1,741 acres, 2019).
| Year | Name | Acres Burned | Distance |
| 2019 | UNNAMED | 1,741 | 100 km |
| 2024 | IBSP SOUTH F1 RX | 690 | 63 km |
| 2024 | RX-HWY Y - SOUTH | 553 | 83 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) | 1.2 in | Driest |
| March | 35°F (2°C) | 2.4 in | |
| April | 47°F (8°C) | 3.7 in | |
| May | 59°F (15°C) | 3.7 in | |
| June | 68°F (20°C) | 4.3 in | Wettest |
| July | 73°F (23°C) | 4.0 in | Warmest |
| August | 70°F (21°C) | 4.2 in | |
| September | 62°F (17°C) | 3.8 in | |
| October | 51°F (10°C) | 2.6 in | |
| November | 37°F (3°C) | 2.7 in | |
| December | 25°F (-4°C) | 2.0 in |
Union has a seasonal temperature swing of 52°F / from 21°F in January to 73°F in July. Total annual precipitation is 36.1 inches, with June being the wettest month (4.3") and February the driest (1.2").