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Weather & Climate in Janesville, IA
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Janesville experiences four distinct seasons with an average annual temperature of 49°F (9°C). Winters average 19°F in January while summers reach 75°F in July. The area gets 260 sunny days per year, above the national average. Annual precipitation totals 36.3 inches. The area receives 39.1 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 908 feet.
Temperature
19°F Jan (-7°C)
75°F Jul (24°C)
| Annual Average | 49.0°F |
| 9% below US avg | |
| January Average | 19°F (-7°C) |
| July Average | 75°F (24°C) |
| Sunny Days | 260 days/yr |
Geography
| Elevation | 908 ft (277 m) |
| Area | 1.4 sq mi (3.6 km²) |
| Population Density | 728/sq mi |
| Coordinates | 42.6458°N, 92.4624°W |
| Timezone | America/Chicago |
| County | Bremer County County |
| Nearest Airport | Waterloo Regional (ALO) 7 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Very Low |
| Risk Score | 24.6 / 100 |
| Social Vulnerability | 10.6 / 100 |
| Community Resilience | 98.0 / 100 |
Hazard Breakdown
| Tornado | Relatively Low |
| Hurricane | Very Low |
| Earthquake | Very Low |
| Wildfire | Very Low |
| Flood | Very Low |
| Hail | Relatively Low |
| Strong Wind | Relatively Low |
| Heat Wave | Very Low |
| Winter Weather | Relatively Low |
| Lightning | Very Low |
| Ice Storm | Very Low |
| Drought | Relatively Moderate |
| Cold Wave | Relatively Low |
| Landslide | Very Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Tornado History
626 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF5. Total: 48 fatalities, 1,190 injuries.
| Date | Rating | Distance | Path | Fatalities |
| May 25, 2008 | EF5 | 36 km | 41.0 mi | 9 |
| May 15, 1968 | EF5 | 56 km | 62.1 mi | 13 |
| May 15, 1968 | EF5 | 44 km | 13.1 mi | 5 |
| Oct 14, 1966 | EF5 | 99 km | 9.7 mi | 6 |
| Mar 13, 1990 | EF4 | 97 km | 19.0 mi | 0 |
| May 30, 1989 | EF4 | 71 km | 11.0 mi | 0 |
| Aug 12, 1974 | EF4 | 87 km | 5.0 mi | 0 |
| Jul 12, 1971 | EF4 | 65 km | 10.9 mi | 0 |
| Apr 30, 1967 | EF4 | 93 km | 13.3 mi | 0 |
| Aug 26, 1965 | EF4 | 44 km | 4.7 mi | 1 |
| May 5, 1965 | EF4 | 76 km | 41.6 mi | 0 |
| Sep 1, 1961 | EF4 | 46 km | 26.6 mi | 0 |
| Apr 30, 1954 | EF4 | 84 km | 80.4 mi | 0 |
| May 10, 1953 | EF4 | 90 km | 162.0 mi | 2 |
| May 10, 1953 | EF4 | 98 km | 26.6 mi | 0 |
| Jul 19, 2018 | EF3 | 78 km | 8.4 mi | 0 |
| May 25, 2008 | EF3 | 37 km | 32.0 mi | 0 |
| Jun 11, 2004 | EF3 | 84 km | 12.0 mi | 0 |
| May 21, 2004 | EF3 | 85 km | 3.0 mi | 0 |
| May 11, 2000 | EF3 | 14 km | 18.6 mi | 1 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Wildfire History
4 wildfires (100+ acres) recorded within 100 km. Largest: UNNAMED (939 acres, 2009).
| Year | Name | Acres Burned | Distance |
| 2009 | UNNAMED | 939 | 88 km |
| 2010 | FOLEY | 786 | 90 km |
| 2011 | ACE AUTO | 676 | 96 km |
| 2011 | IRCP WUI ROFAE #2 FY11 | 510 | 84 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 19°F (-7°C) | 0.9 in | Coldest, Driest |
| February | 22°F (-5°C) | 1.0 in | |
| March | 35°F (2°C) | 2.3 in | |
| April | 48°F (9°C) | 3.5 in | |
| May | 60°F (16°C) | 4.2 in | |
| June | 70°F (21°C) | 4.5 in | |
| July | 75°F (24°C) | 4.7 in | Warmest, Wettest |
| August | 71°F (22°C) | 4.1 in | |
| September | 63°F (17°C) | 3.5 in | |
| October | 51°F (10°C) | 2.6 in | |
| November | 35°F (2°C) | 1.9 in | |
| December | 21°F (-6°C) | 1.3 in |
Janesville has a seasonal temperature swing of 55°F / from 19°F in January to 75°F in July. Total annual precipitation is 34.5 inches, with July being the wettest month (4.7") and January the driest (0.9").