Monona County

Every recorded tornado

1. Injuries and deaths are for the tornado’s whole path, which may extend beyond the county. Deaths recorded within Monona County: 4.
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.

More event types since 1996

Costliest events since 1996

1. Aug 1, 2011Flood$5.0 million
   National Weather Service narrative

   Flooding along the Missouri River gradually worsened over Monona county during June and July as record releases from Gavins Point Dam brought widespread flooding along the river. Conditions improved markedly during August as releases were reduced and the river level at Decatur dropped below flood stage late in the month. Flooding in Monona county was mainly confined to agricultural lowlands, recreation areas and roads near the river. However, Blencoe started sandbag operations in June as did other businesses from Blencoe to Onawa. The flooding forced the post office in Blencoe to move operations to a nearby town. Late in June the Highway 175 bridge over the Missouri between…

2. Mar 13, 2019Flood$4.2 million
   National Weather Service narrative

   This is for flooding along the Maple River. The river gage at Mapleton, operated by the USGS, peaked at 23.60 feet at 6:15 pm on March 14th. Minor flood stage is 21 feet, moderate flood stage is 24 feet . Preliminarily this peak is the 2nd highest on record. Ice jamming may have played a role in the flooding at this location. The flooding caused damage and the closure of Hwy. 183 West of Mapleton. Hwy 175 south of Mapleton and the closure of Hwy. 175 North of Mapleton. Also the local Airport was totally flooded and damaged. Flood totals are for for the County including from damage caused by flooding of the Soldier River.

3. Jul 16, 1996Flood, Monona$1.5 million
   National Weather Service narrative

   The evening of July 16th thunderstorms produced a large area of 10 plus inches of rain from Monona County into Crawford County. Over half of Monona County averaged between 8 and 10 inches of rain. 12.75 inches of rain was reported at the Castana Experimental Farm. Extensive crop damage resulted across the county. Damage was also done to roads and bridges.

4. May 5, 2007Flash Flood$1.4 million
   National Weather Service narrative

   Rainfall of 3 to 4 inches produce flash flooding of streets in Onawa. Other creeks across the county flooded county roads causing road, bridge and levee damage.

5. Jun 24, 2024Flood$1.0 million
   National Weather Service narrative

   River flooding from upstream excessive rain impacted the region, bringing the Missouri River to moderate flood stage. The Missouri River crested at 37.55 feet at the Decatur gauge at 03:45 CDT on 6/26. Flood stage at this gauge is 35.0 feet. Additional flooding for the same reason was observed on Little Sioux River between 6/24 and 6/28. The Little Sioux river crested at 27.33 feet. Flood stage for this river in Monona County is 25.0 feet. At 04:56 am CDT on the 25th, law enforcement reported that a levee on the Little Sioux River failed 600 yards south of Highway 141 resulting in flash flooding in the surrounding areas. Later that same day shortly after 04:00 pm CDT, law…

6. May 16, 1999Tornado$120,000
   National Weather Service narrative

   Two homes sustained moderate to major damage, 3 grain bins and other outbuildings destroyed. Several vehicles were carried some distance. Large tree uprooted.

7. Jun 25, 2024Flash Flood$100,000
   National Weather Service narrative

   At 04:56 am CDT on the 25th, law enforcement reported that a levee on the Little Sioux River failed 600 yards south of Highway 141 resulting in flash flooding in the surrounding areas. Since this event was tied to the river flooding at the end of this month, the damage estimates for the Flood event for Monona County has the damage estimates for this levee break included in it.

8. Jun 30, 2014Flash Flood$50,000
   National Weather Service narrative

   Heavy rainfall caused several inches of water on roads in the city of Mapleton, as well as on the county roads outside of town. Rainfall of 1.80 inches was reported in a half hour leading to the flash flooding.

9. Jul 1, 2011Flood$50,000
   National Weather Service narrative

   Flooding along the Missouri River gradually worsened over Monona county during June and continued through July as record releases from Gavins Point Dam brought widespread flooding along the River. Flooding in Monona county initially was mainly confined to agricultural lowlands, recreation areas and roads near the river but then started threatening Blencoe which started sandbag operations in June as did other businesses from Blencoe to Onawa. The flooding forced the post office in Blencoe to move operations to a nearby town and closed 2 casinos. Late in June the Highway 175 bridge over the Missouri between Decatur and Onawa was closed due to erosion of the abutment on the Iowa side…

10. Apr 15, 2012Strong Wind, Monona$40,000
    National Weather Service narrative

    Sustained south winds of 25 to 35 mph with gusts between 45 and 55 mph for several hours caused scattered damage in the Onawa area. At least one tree was toppled and a building that was being demolished had the debris scattered over a large area.

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

106°FJul 29, 1947

All-time low

−35°FFeb 16, 2021

Warmest night

80°F2 times, most recently Jul 14, 1980

Coldest day

−15°FDec 24, 1983

Wettest day

9.77 inJul 17, 1996

Snowiest day

12.0 inMar 5, 1963

Hottest year

1987mean 52.1°F

Coldest year

1951mean 45.2°F

Wettest year

201443.37 in

Driest year

195515.35 in

Snowiest season

63.4 in1961-62

Station Mapleton NO.2 (USC00135123), 1,180 ft elevation, 14.8 miles from the population centre. Daily records from 1937 to October 27, 2026; 93.6% 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 USC00135123.
• 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.