Union County

Every recorded tornado

1. Injuries and deaths are for the tornado’s whole path, which may extend beyond the county. Deaths recorded within Union County: 0.
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.

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.

More event types since 1996

Costliest events since 1996

1. Jun 21, 2024Flood$54.5 million
   National Weather Service narrative

   Rainfall amounts across Union County from June 20-22 ranged from around a third of an inch across southern areas to 1 to 2 inches across northern areas. Farther north and upstream, 6 to 10 inches of rain fell across portions of southeast South Dakota and northwest Iowa, with locally higher amounts in excess of 12 inches. ||This rainfall resulted in record flooding along the Big Sioux River and extensive overland flooding along the adjoining flood plain. County-wide, 44 residences were destroyed and another 182 received minor to major flood damage. Estimated losses exceed 52 million dollars. At the peak of the flooding, there were an estimated 20 to 30 water rescues. ||Residents…

2. Aug 10, 2020Lightning$2.5 million
   National Weather Service narrative

   Lightning struck a single-story apartment building and initiated a fire which burned through the entire attic of the building. Crews from North Sioux City and three nearby cities attacked the fire for around two hours. All twenty apartments were severely damaged, displacing all residents. Property damage costs are rough estimates.

3. Mar 13, 2019Flood$1.2 million
   National Weather Service narrative

   Flooding resulted in extensive damage to public infrastructure including numerous county and township roads, culverts, and some bridges.

4. Jun 15, 2014Flood$1.0 million
   National Weather Service narrative

   Repeated heavy rains caused record flooding of the Big Sioux River. Farmland and other lowlands including numerous roads were flooded. Some roads were damaged, and some secondary roads were washed out. A few farm homes, other farm buildings, and some fences were damaged by floodwaters. The river crested at a record 12.92 feet above flood stage at Hawarden, Iowa on June 17th. Interstate 29 was temporarily closed along a 22 mile stretch to facilitate levee building to divert some Big Sioux River water to McCook Lake, but the Interstate was re-opened when the river crested at a lower level than was feared. A levee breach across the river from Akron, Iowa, briefly aggravated lowland…

5. Jun 5, 1999Hail$300,000
   National Weather Service narrative

   Large hail broke many windows and damaged vehicles and homes, mainly in Jefferson. The hail also caused crop damage over a large area from near Jefferson to near Richland.

6. Oct 4, 2013Tornado$250,000
   National Weather Service narrative

   A tornado crossed the Missouri River from Dakota County in Nebraska and entered Union County. The tornado severely damaged the roof of a house, and collapsed a chimney, carport and porch roof, and the walls of a garage in the same house. The tornado also caused tree damage, including trunks snapped, overturned an irrigation system, and damaged the roof, siding, and/or gutters of at least four other houses.

7. Oct 4, 2013Tornado$200,000
   National Weather Service narrative

   A tornado severely damaged the roof and gutters of a house, and the walls and roof of at least two storage equipment buildings. The tornado caused tree damage, including trunks snapped and large branches blown down, damaged a road sign, blew down or crushed several grain bins, blew down power poles and lines, and flattened corn crops. One of the destroyed grain bins was wrapped around a house, causing damage to the roof, siding, and gutters of the house. The tornado then crossed the Big Sioux River into Plymouth County Iowa.

8. Aug 2, 2001Thunderstorm Wind$200,000
   National Weather Service narrative

   Thunderstorm winds caused widespread damage to trees, power poles, and lines, resulting in power outages affecting most of North Sioux City. Some large trees were sheared from their trunks. Tree debris damaged vehicles, homes, garages, and sheds.

9. Sep 23, 2010Flood$100,000
   National Weather Service narrative

   Widespread heavy rain, combined with saturated ground, caused a fairly rapid rise of the Big Sioux River to moderate to major flooding levels. Roads and numerous agricultural land near the river were flooded, as well as a few homes. A dike break just south of Big Springs caused additional farmland to be flooded. The river crested at 6.9 feet above flood stage near Akron, Iowa on September 27th.

10. Jul 16, 1996Heavy Rain$100,000
    National Weather Service narrative

    Heavy rain of 6 to 10 inches fell over southern Union County and caused lowland and basement flooding, with the worst conditions reported at Dakota Dunes.

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

108°F2 times, most recently Jul 12, 1995

All-time low

−28°F3 times, most recently Feb 16, 2021

Warmest night

81°FJun 21, 2025

Coldest day

−13°FDec 21, 1989

Wettest day

5.50 inJul 17, 1972

Snowiest day

18.4 inMar 15, 2004

Hottest year

2012mean 52.5°F

Coldest year

1996mean 45.1°F

Wettest year

201441.36 in

Driest year

197614.33 in

Snowiest season

65.9 in1961-62

Station Sioux City Airport (USW00014943), 1,092 ft elevation, 22.7 miles from the population centre. Daily records from 1940 to October 26, 2026; 100.0% 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 USW00014943.
• 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.
• 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.