Johnson County

Every recorded tornado

1. Injuries and deaths are for the tornado’s whole path, which may extend beyond the county. Deaths recorded within Johnson County: 1.
2. Weak tornadoes were under-recorded before Doppler radar coverage became national in the early 1990s, so earlier decades read low. Ratings use the Fujita scale before February 2007 and the Enhanced Fujita scale after.

Storm Prediction Center severe weather database, 1950 to 2025.

Smoke overhead

1. A smoke day is a date on which a smoke plume traced by NOAA Hazard Mapping System analysts from satellite imagery covered this place's point (the county's population centre or the city centre). Counts here are of medium or heavy smoke. Since 2018 analysts have often drawn light smoke as one area over most of the continent, so light-smoke counts are not comparable from year to year. The plumes show smoke anywhere in the air above, not air quality at the ground, and smoke hidden by cloud is missed.

NOAA Hazard Mapping System smoke analysis, 2011 to 2026, retrieved October 30, 2026.

Claims by ZIP code

This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).

OpenFEMA NFIP Redacted Claims v3, refreshed August 4, 2026. NOAA Storm Events through 2026.

River crests

River gauges

1. Crests are the highest and the recent crests the National Weather Service lists for each river gauge in the county that has a flood stage, not every flood. Flood categories use each gauge's current flood stages; crests from before levees, dams or channel changes may not be comparable. Crests measured on an old datum are left out of the rankings.

NOAA National Water Prediction Service gauge records, retrieved October 30, 2026.

1. The Palmer Drought Severity Index is computed by NOAA each month from the county's average temperature and precipitation, relative to the county's own climate. Zero is normal; -3 or lower is severe drought and -4 or lower extreme drought. It describes the long-term balance of moisture, not water supply or crop losses.

NOAA NCEI nClimDiv county Palmer Drought Severity Index, 1895 to September 2026, issued October 6, 2026.

Every earthquake of magnitude 4 or more within 50 miles

1. Earthquakes of magnitude 2.5 or more in the USGS Comprehensive Catalog since 1900. Within 50 miles means the epicentre lies within 50 miles of the county boundary (or inside the county).
2. Small earthquakes were under-recorded before the modern seismic networks of the 1970s and are still missed in remote areas, so early decades read low. Magnitudes are as the catalogue reports them and mix scales (moment, local and body-wave).

USGS ANSS Comprehensive Earthquake Catalog, 1900 to present, retrieved October 30, 2026.

Mapped landslides

Mapped by NASA (1).

1. Landslides mapped in the USGS compilation of landslide inventories across the United States (version 3.0, 2025), rated probable or better. The compilation joins inventories made by federal and state agencies for different purposes and areas, so the number mapped in a county reflects how closely it has been surveyed as much as how often its slopes fail. An area with few records may simply not have been mapped. Deaths are as recorded in the inventories; a slide listed in two inventories is counted once.

USGS Landslide Inventories across the United States, version 3.0, retrieved October 27, 2026.

More event types since 1996

Costliest events since 1996

1. Jun 1, 2008Flood$230 million
   National Weather Service narrative

   The record crest on the Iowa River at Iowa City occurred on June 15, 2008 at 31.53 feet. Flood stage is 22 feet. The record crest on the Iowa River at Lone Tree occurred on June 15, 2008 at 23.15 feet. Flood stage is 15 feet. Preliminary damage estimates just to the University of Iowa at Iowa City was at least $230 million. This compares to $6 million in damages during the Great Flood of 1993. Water flowed over the spillway at the Corps of Engineer's Coralville Reservoir for only the third time since the reservoir began operation on September 17, 1958. (The previous two times occurred in the summer of 1993). The result was unprecedented flooding downstream of the reservoir in the…

2. May 18, 1997Hail$40.0 million
   National Weather Service narrative

   A 15 minute "rain" of baseball sized hail caused $30 to $50 million dollars of damage. One insurance agent said "this was the worst storm since 1967." He went on to say; "everyone he insures who has a skylight now has a broken skylight." This included the skylights over the swimming pool in the downtown Iowa City Holliday Inn. The average home claim was $3500 and the average car claim was $2500. The hail caused widespread damage to individuals cars and between 300 and 500 thousand dollars worth of damage to each of four car dealerships interviewed.

3. Jun 29, 1998Thunderstorm Wind$30.7 million
   National Weather Service narrative

   Supercell thunderstorms developed over Central Iowa and rapidly intensified into a long squall line which raced southeast over Eastern Iowa into Central Illinois. Numerous funnel clouds were sited along the leading edge of the storm and a few non-supercell tornadoes were masked within a large area of damaging winds. Straightline winds from 60 to over 120 mph produced the most serious damage with these storms and 8 counties in Eastern Iowa were declaired disaster areas. School-net stations measured winds at 69 mph in Cedar Rapids and 123 mph at Washington. Across the county warning area sustained winds of 70 to 80 mph ripped down trees, power lines, and windmills, and knocked over…

4. Apr 13, 2006Tornado$12.0 million
   National Weather Service narrative

   Rated very high F2 with winds estimated at 155 mph.

5. May 15, 1998Tornado$6.0 million
   National Weather Service narrative

   A tornado developed two miles Southwest of Washington Iowa and produced a 30 mile long continuous path of damage and debris as it moved to the Northeast at nearly 30 mph. The tornado weakened and lifted before reaching I-80 near West Branch Iowa shortly before 6pm. The tornado continued Northeast across Cedar County Iowa producing another 15 miles of isolated damage...not continuous. The storm producing this tornado continued Northeast producing a brief touchdown one mile west of Oxford Mills Iowa near the intersection of county roads E53 and X64. Another brief touchdown occurred south of Dubuque near Zwingle Iowa before the storm moved into Wisconsin. In Washington Iowa extensive…

6. Aug 11, 2016Flash Flood$1.5 million
   National Weather Service narrative

   The Emergency Manager reported that the Cedar Rapids and Iowa City Railroad (CRANDIC) experienced washed out tracks and a bridge in the Swisher area.

7. Feb 24, 2007Ice Storm, Johnson$1.0 million
   National Weather Service narrative

   A widespread and crippling ice/snow storm affected eastern Iowa, northwest and western Illinois, and extreme northeast Missouri on February 24, 2007. This massive ice storm was the worst to affect the region since January 22-23, 1965. Ice accumulations of around one inch were common, with some reports to near two inches! To make matters worse, east winds gusting over 50 mph, combined with the heavy ice accumulation, brought down numerous tree branches and power lines, along with several thousand power poles. There were even whole trees crashing down from the weight of the ice. Widespread power outages occurred, affecting over 180,000 people, which lasted more than a week in some…

8. Apr 13, 2006Lightning$515,000
   National Weather Service narrative

   Sometime between 1900 and 1930 CST lightning struck a brand new home in Coralville. The resultant fire destroyed the home and strong winds allowed the flames to spread onto a house nearing completion next door.

9. Jun 22, 2007Flash Flood$500,000
   National Weather Service narrative

   Reports of urban flash flooding were received from around Iowa City. 8 to 10 inches of water covered a parking lot at a radio station, stranding 5 employees. 4 of the 5 were evacuated by the fire department. Numerous major streets were closed, and some businesses suffered minor flooding damage.

10. May 24, 1996High Wind, Johnson$500,000
    National Weather Service narrative

    Strong gradient winds caused widespread tree damage and downed power lines. Damage was most extensive in the Iowa City, Iowa area where trees block many streets limiting traffic and causing an extended power outage. In Davenport Iowa, tree damage was less extensive shingles were blown off some area roofs.

1. Storm Events records before 1996 cover only tornadoes, thunderstorm wind and hail. Damage figures are as reported by the National Weather Service at the time, not adjusted for inflation.

NOAA NCEI Storm Events Database, 1950 to 2026, issued October 26, 2026.

All-time high

105°F3 times, most recently Jul 25, 2012

All-time low

−34°FFeb 3, 1996

Warmest night

80°FJul 19, 2019

Coldest day

−14°FFeb 2, 1996

Wettest day

5.65 inJun 22, 2007

Hottest year

2024mean 53.8°F

Coldest year

1951mean 46.1°F

Wettest year

201848.78 in

Driest year

199920.47 in

Station Iowa City Municipal Airport (USW00014937), 652 ft elevation, 3.2 miles from the population centre. Daily records from 1948 to October 26, 2026; 99.5% of days in the last 30 years are complete. Records at a single station can differ from a city’s official threaded record, which may combine several stations.

NOAA NCEI Global Historical Climatology Network Daily.

This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).

OpenFEMA Disaster Declarations Summaries, retrieved October 30, 2026. Statewide declarations are not listed.

Neighbouring counties

• Tornadoes NOAA Storm Prediction Center severe weather database, through 2025.
• Tropical cyclones NOAA National Hurricane Center HURDAT2 (Atlantic; Northeast and Central Pacific), through 2025.
• Wildfire USGS/USFS Monitoring Trends in Burn Severity, through 2026.
• Storm events NOAA NCEI Storm Events Database, through 2026.
• Flood insurance OpenFEMA NFIP Redacted Claims v3, refreshed August 4, 2026.
• Declarations OpenFEMA Disaster Declarations Summaries v2, retrieved October 30, 2026.
• Weather records NOAA NCEI Global Historical Climatology Network Daily, station USW00014937.
• River crests NOAA National Weather Service, National Water Prediction Service river gauges, retrieved October 30, 2026.
• Drought NOAA NCEI nClimDiv county Palmer Drought Severity Index, through September 2026.
• Smoke NOAA NESDIS Hazard Mapping System smoke analysis, retrieved October 30, 2026.
• Landslides USGS Landslide Inventories across the United States, version 3.0 (2025).
• Earthquakes USGS ANSS Comprehensive Earthquake Catalog (ComCat), retrieved October 30, 2026.

Joins, thresholds and known limits are set out in the methodology. Found an error? Report it. Page built October 30, 2026.