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Weather & Climate in Johnston, IA
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Johnston experiences four distinct seasons with an average annual temperature of 50°F (10°C). Winters average 22°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 36.2 inches. The area receives 38.0 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 833 feet.
Temperature
22°F Jan (-6°C)
75°F Jul (24°C)
| Annual Average | 50.3°F |
| 7% below US avg | |
| January Average | 22°F (-6°C) |
| July Average | 75°F (24°C) |
| Sunny Days | 275 days/yr |
Geography
| Elevation | 833 ft (254 m) |
| Area | 18.3 sq mi (47.5 km²) |
| Population Density | 1,241/sq mi |
| Coordinates | 41.6920°N, 93.7245°W |
| Timezone | America/Chicago |
| County | Polk County County |
| Nearest Airport | Des Moines International (DSM) 13 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively Moderate |
| Risk Score | 92.0 / 100 |
| Social Vulnerability | 17.0 / 100 |
| Community Resilience | 91.2 / 100 |
Hazard Breakdown
| Tornado | Relatively High |
| Hurricane | Very Low |
| Earthquake | Relatively Low |
| Wildfire | Very Low |
| Flood | Relatively Moderate |
| Hail | Relatively High |
| Strong Wind | Very High |
| Heat Wave | Relatively High |
| Winter Weather | Relatively High |
| Lightning | Relatively Moderate |
| Ice Storm | Relatively High |
| Drought | Relatively High |
| Cold Wave | Relatively High |
| Landslide | Relatively Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Tornado History
712 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF5. Total: 20 fatalities, 396 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Jun 13, 1976 | EF5 | 29 km | 21.3 mi | 0 |
| Jun 27, 1953 | EF5 | 86 km | 0.1 mi | 1 |
| Mar 5, 2022 | EF4 | 65 km | 70.6 mi | 6 |
| Apr 8, 1999 | EF4 | 89 km | 56.0 mi | 0 |
| May 27, 1995 | EF4 | 77 km | 30.0 mi | 0 |
| May 27, 1995 | EF4 | 90 km | 57.0 mi | 0 |
| May 30, 1989 | EF4 | 80 km | 11.0 mi | 0 |
| May 24, 1989 | EF4 | 60 km | 66.0 mi | 0 |
| Sep 28, 1986 | EF4 | 12 km | 20.0 mi | 0 |
| May 4, 1977 | EF4 | 100 km | 2.0 mi | 0 |
| Jun 18, 1974 | EF4 | 10 km | 15.3 mi | 2 |
| Jun 8, 1967 | EF4 | 99 km | 2.0 mi | 0 |
| May 5, 1965 | EF4 | 92 km | 9.9 mi | 0 |
| May 10, 1959 | EF4 | 78 km | 41.1 mi | 0 |
| May 10, 1953 | EF4 | 97 km | 6.4 mi | 0 |
| Mar 5, 2022 | EF3 | 88 km | 11.3 mi | 1 |
| Aug 20, 2019 | EF3 | 51 km | 5.4 mi | 0 |
| Jul 19, 2018 | EF3 | 72 km | 8.4 mi | 0 |
| Jul 19, 2018 | EF3 | 70 km | 9.2 mi | 0 |
| Jun 22, 2015 | EF3 | 77 km | 11.1 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Wildfire History
1 wildfire (100+ acres) recorded within 100 km. Largest: NEAL SMITH WUI 2016 1 (1,050 acres, 2016).
| Year | Name | Acres Burned | Distance |
| 2016 | NEAL SMITH WUI 2016 1 | 1,050 | 39 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 22°F (-6°C) | 0.9 in | Coldest, Driest |
| February | 25°F (-4°C) | 1.0 in | |
| March | 37°F (3°C) | 2.2 in | |
| April | 50°F (10°C) | 3.4 in | |
| May | 61°F (16°C) | 4.2 in | |
| June | 71°F (21°C) | 4.8 in | Wettest |
| July | 75°F (24°C) | 3.9 in | Warmest |
| August | 73°F (23°C) | 4.1 in | |
| September | 64°F (18°C) | 3.4 in | |
| October | 52°F (11°C) | 2.6 in | |
| November | 37°F (3°C) | 1.8 in | |
| December | 24°F (-4°C) | 1.2 in |
Johnston has a seasonal temperature swing of 54°F / from 22°F in January to 75°F in July. Total annual precipitation is 33.6 inches, with June being the wettest month (4.8") and January the driest (0.9").