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Weather & Climate in McHenry, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
McHenry experiences four distinct seasons with an average annual temperature of 49°F (9°C). Winters average 22°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 37.0 inches. The area receives 34.5 inches of snow annually, a moderate snowfall amount. Air quality is rated Good with a median AQI of 43. 67% of days have good air quality. The city sits at an elevation of 809 feet.
Temperature
22°F Jan (-6°C)
73°F Jul (23°C)
| Annual Average | 48.6°F |
| 10% below US avg | |
| January Average | 22°F (-6°C) |
| July Average | 73°F (23°C) |
| Sunny Days | 260 days/yr |
Geography
| Elevation | 809 ft (247 m) |
| Area | 15.0 sq mi (39.0 km²) |
| Population Density | 1,873/sq mi |
| Coordinates | 42.3362°N, 88.2917°W |
| Timezone | America/Chicago |
| County | McHenry County County |
| Nearest Airport | Kenosha Regional (ENW) 26 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
| Good Days % | 66.9% |
| Unhealthy Days | 1 |
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 | 110 km | 10 km |
| Feb 10, 2010 | 2 km NW of Lily Lake, Illinois | M3.8 | 44 km | 10 km |
| Sep 2, 1999 | 8 km W of Amboy, Illinois | M3.5 | 117 km | 5 km |
| Nov 4, 2013 | 1 km SSW of Lyons, Illinois | M3.2 | 71 km | 1 km |
| Jul 15, 2024 | 2 km WNW of Somonauk, Illinois | M3.1 | 84 km | 10 km |
| Mar 25, 2015 | 3 km WNW of Lake in the Hills, Illinois | M2.9 | 18 km | 6 km |
| Jun 10, 2013 | 4 km NNE of Virgil, Illinois | M2.6 | 43 km | 5 km |
| Mar 15, 2025 | 6 km W of Dwight, Illinois | M2.6 | 140 km | 5 km |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Tornado History
540 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF5. Total: 109 fatalities, 2,207 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Aug 28, 1990 | EF5 | 73 km | 16.4 mi | 29 |
| Apr 9, 2015 | EF4 | 98 km | 30.1 mi | 2 |
| Apr 27, 1984 | EF4 | 72 km | 6.5 mi | 1 |
| Jun 29, 1979 | EF4 | 91 km | 5.4 mi | 0 |
| Jun 13, 1976 | EF4 | 78 km | 3.3 mi | 2 |
| Sep 28, 1972 | EF4 | 35 km | 5.2 mi | 0 |
| Apr 21, 1967 | EF4 | 53 km | 25.5 mi | 24 |
| Apr 21, 1967 | EF4 | 21 km | 8.8 mi | 1 |
| Apr 21, 1967 | EF4 | 83 km | 15.0 mi | 33 |
| Apr 11, 1965 | EF4 | 15 km | 9.1 mi | 6 |
| Jun 20, 2021 | EF3 | 66 km | 17.6 mi | 0 |
| Jan 7, 2008 | EF3 | 45 km | 13.2 mi | 0 |
| Jan 7, 2008 | EF3 | 24 km | 10.8 mi | 0 |
| Mar 27, 1991 | EF3 | 86 km | 15.0 mi | 0 |
| Apr 27, 1984 | EF3 | 88 km | 9.0 mi | 1 |
| Jun 5, 1980 | EF3 | 97 km | 10.7 mi | 0 |
| Mar 12, 1976 | EF3 | 79 km | 22.6 mi | 0 |
| Jan 24, 1967 | EF3 | 93 km | 24.9 mi | 0 |
| Jul 19, 1963 | EF3 | 27 km | 10.6 mi | 0 |
| Jun 22, 2024 | EF2 | 75 km | 6.0 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 | 136 km |
Source: NOAA/NCEI Historical Tsunami Database.
Wildfire History
2 wildfires (100+ acres) recorded within 100 km. Largest: IBSP SOUTH F1 RX (690 acres, 2024).
| Year | Name | Acres Burned | Distance |
| 2024 | IBSP SOUTH F1 RX | 690 | 40 km |
| 2024 | RX-HWY Y - SOUTH | 553 | 79 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 22°F (-6°C) | 1.6 in | Coldest |
| February | 24°F (-4°C) | 1.3 in | Driest |
| March | 35°F (2°C) | 2.5 in | |
| April | 46°F (8°C) | 3.6 in | |
| May | 58°F (14°C) | 3.4 in | |
| June | 67°F (20°C) | 4.0 in | |
| July | 73°F (23°C) | 4.1 in | Warmest, Wettest |
| August | 70°F (21°C) | 4.1 in | |
| September | 62°F (17°C) | 3.9 in | |
| October | 51°F (10°C) | 2.5 in | |
| November | 38°F (3°C) | 2.7 in | |
| December | 25°F (-4°C) | 2.1 in |
McHenry has a seasonal temperature swing of 51°F / from 22°F in January to 73°F in July. Total annual precipitation is 35.6 inches, with July being the wettest month (4.1") and February the driest (1.3").