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Weather & Climate in Marietta, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Marietta experiences four distinct seasons with an average annual temperature of 53°F (11°C). Winters average 25°F in January while summers reach 77°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 41.0 inches. The area receives 27.9 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 640 feet.
Temperature
25°F Jan (-4°C)
77°F Jul (25°C)
| Annual Average | 52.5°F |
| 3% below US avg | |
| January Average | 25°F (-4°C) |
| July Average | 77°F (25°C) |
| Sunny Days | 275 days/yr |
Geography
| Elevation | 640 ft (195 m) |
| Area | 0.1 sq mi (0.3 km²) |
| Population Density | 407/sq mi |
| Coordinates | 40.4995°N, 90.3930°W |
| Timezone | America/Chicago |
| County | Fulton County County |
| Nearest Airport | General Downing - Peoria International (PIA) 38 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively Low |
| Risk Score | 59.0 / 100 |
| Social Vulnerability | 35.9 / 100 |
| Community Resilience | 77.6 / 100 |
Hazard Breakdown
| Tornado | Relatively Moderate |
| Hurricane | Very Low |
| Earthquake | Relatively Low |
| Wildfire | Very Low |
| Flood | Relatively Low |
| Hail | Relatively Moderate |
| Strong Wind | Relatively Moderate |
| Heat Wave | Relatively Low |
| Winter Weather | Relatively Low |
| Lightning | Relatively Low |
| Ice Storm | Relatively Moderate |
| Drought | Relatively Moderate |
| Cold Wave | Relatively Moderate |
| Landslide | Relatively Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Tornado History
621 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF4. Total: 12 fatalities, 596 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Nov 17, 2013 | EF4 | 71 km | 46.4 mi | 3 |
| Jul 13, 2004 | EF4 | 96 km | 9.6 mi | 0 |
| May 13, 1995 | EF4 | 16 km | 7.0 mi | 0 |
| May 13, 1995 | EF4 | 78 km | 50.0 mi | 0 |
| Jun 29, 1976 | EF4 | 64 km | 4.9 mi | 0 |
| Apr 4, 2023 | EF3 | 20 km | 19.9 mi | 0 |
| Feb 28, 2017 | EF3 | 98 km | 17.8 mi | 0 |
| Dec 31, 2010 | EF3 | 73 km | 3.6 mi | 0 |
| Aug 19, 2009 | EF3 | 93 km | 24.3 mi | 0 |
| May 10, 2003 | EF3 | 60 km | 17.5 mi | 0 |
| Apr 8, 1999 | EF3 | 91 km | 7.5 mi | 0 |
| Apr 19, 1996 | EF3 | 91 km | 9.4 mi | 0 |
| May 13, 1995 | EF3 | 40 km | 25.0 mi | 0 |
| May 9, 1995 | EF3 | 89 km | 50.0 mi | 0 |
| Jun 21, 1981 | EF3 | 36 km | 8.8 mi | 1 |
| Aug 15, 1978 | EF3 | 92 km | 6.4 mi | 0 |
| Jul 26, 1978 | EF3 | 94 km | 8.9 mi | 0 |
| Jul 23, 1975 | EF3 | 20 km | 14.0 mi | 2 |
| Jul 23, 1975 | EF3 | 8 km | 11.1 mi | 0 |
| Jun 13, 1975 | EF3 | 23 km | 6.6 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Wildfire History
5 wildfires (100+ acres) recorded within 100 km. Largest: UNIT 3 (1,206 acres, 1999).
| Year | Name | Acres Burned | Distance |
| 1999 | UNIT 3 | 1,206 | 90 km |
| 2002 | HSB 03 2 | 1,130 | 91 km |
| 2000 | DESTRUST A | 756 | 91 km |
| 2006 | HSB 003 | 674 | 90 km |
| 2004 | HSB 009 | 608 | 91 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 25°F (-4°C) | 1.5 in | Coldest |
| February | 29°F (-2°C) | 1.4 in | Driest |
| March | 40°F (5°C) | 3.0 in | |
| April | 52°F (11°C) | 3.7 in | |
| May | 63°F (17°C) | 4.0 in | |
| June | 72°F (22°C) | 3.9 in | |
| July | 77°F (25°C) | 4.1 in | Warmest, Wettest |
| August | 73°F (23°C) | 3.5 in | |
| September | 66°F (19°C) | 3.9 in | |
| October | 54°F (12°C) | 3.0 in | |
| November | 41°F (5°C) | 2.8 in | |
| December | 29°F (-2°C) | 2.3 in |
Marietta has a seasonal temperature swing of 52°F / from 25°F in January to 77°F in July. Total annual precipitation is 37.1 inches, with July being the wettest month (4.1") and February the driest (1.4").