Harrison County

Every recorded tornado

1. Injuries and deaths are for the tornado’s whole path, which may extend beyond the county. Deaths recorded within Harrison County: 2.
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.

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.

Costliest events since 1996

1. May 5, 2007Flash Flood$15.0 million
   National Weather Service narrative

   Rainfall of 5 inches fell across the Missouri Valley area Saturday May 5th prompting the levee along Willow Creek to eventually fail causing substantial flash flooding in and around the Missouri Valley area. |Initally flash flooding was observed due to the heavy rain Saturday evening the 5th near Highway 30 and county road 66. The levee failure caused more substantial flash flooding early Sunday the 6th with many residents barely able to escape the rising flood waters. The area most affected was the southwest part of town, which sat below the bluffs where most of the town is located. At least 77 homes and 6 businesses were flooded and declared an almost complete loss. Many…

2. Jun 21, 1996Flood, Harrison$7.5 million
   National Weather Service narrative

   Harrison County received record flooding along the Boyer River along the entire reach. From the 19th of June to the 23rd, parts of northwest Iowa upstream from Harrison County was inundated with as much as 13 inches of rain. Locally, 2 to 5 inches was reported. The heavy rain to the north traveled downstream, in addition to the locally heavy rains, and resulted in local levee breaks near Woodbine and Missouri Valley. Extensive damage to crops, roads, bridges, and culverts were reported.

3. Aug 1, 2011Flood$7.0 million
   National Weather Service narrative

   Flooding along the Missouri River gradually worsened over the area during June and July and continued into August as record releases from Gavins Point Dam brought widespread flooding along the River. The river near Blair climbed to a little under 33 feet by the end of June, flood stage is 26.5 feet, before falling slightly during July and a little more in early to mid August. However, by late August decreased releases from Gavins Point Dam had allowed the river near Blair to fall to around 28 feet. County roads and highways, some homes and farmland and parts of Interstate 29 were flooded along with several parks and recreation areas near the river. Sand bag operations were used…

4. Mar 13, 2019Flood$2.2 million
   National Weather Service narrative

   Thiere was for flooding along the Boyer River. The river gauge at Logan, operated by the USGS, peaked at 25.33 feet at 7 pm on March 13th. Major flood stage is 25 feet. Preliminary information shows this peak is the highest on record. Portions of the town of Missouri Valley flooded from the flood. Highway 30 closed in Woodbine. A levee topped by floodwaters at 296th street in Missouri Valley, on the east side of the levee around 2 miles northeast of town. Also 2 breaches in the levee around Willow Creek. Evacuations took place in Missouri Valley. Property damage totals are for the entire county from flooding of the Boyer River, Willow Creek, and Missouri River.

5. May 16, 1999Tornado$1.9 million
   National Weather Service narrative

   The stronger of the 2 tornadoes that ripped through Harrison county the afternoon of 5/16/99 killed 2 people and destroyed 6 homes and a bridge before it dissipated a couple of miles east of Logan. A family of 5 leaving a high school graduation party encountered the tornado on a road around 6 miles northeast of Missouri Valley and took cover in a ditch about the time the path of the tornado widened to a quarter mile. Two of them were killed after their car and a 3-ton combine head were thrown on them. There were also numerous flipped or smashed vehicles in this area.

6. Jul 16, 1996Flood, Harrison$1.5 million
   National Weather Service narrative

   Heavy rains upstream in Monona and Crawford Counties of 5 to nearly 13 inches brought flooding along the entire Boyer River and the Soldier River. Urban flooding affected Pisgah and Missouri Valley. Up to 6 inches of rain fell in Harrison County itself. Damage was substantial to cropland, bridges, county roads, farm fences, and culverts.

7. Oct 25, 1997Heavy Snow, Harrison$800,000
   National Weather Service narrative

   A major early season snowstorm struck portions of southwestern Iowa, blanketing the area with 6 to 9 inches of heavy wet snow. The snow fell on trees, many of which were still fully or partially leafed, and caused extensive damage and/or total destruction. Thousands of residents were without power just after the storm and many of the outages lasted for several days. Emergency shelters were opened in the affected areas for use by those who suffered a hardship from the storm.

8. May 12, 2023Flash Flood$500,000
   National Weather Service narrative

   Forest Service reported up to two dozen culverts washed out and six county roads that were partially or fully washed out. Large trees were washed into fields and there was significant damage to farm fields in several areas in the counties. There are significant areas of crop fields that likely lost in excess of 100 tons per acre from that one heavy rain event. The county estimated the damage to be approximately $400,000-$600,000.

9. Jun 24, 2024Flood$200,000
   National Weather Service narrative

   Excessive rainfall across much of eastern South Dakota resulted in river flooding along the Missouri River at the end of June. Moderate flood stage was observed along the Missouri, with the Blair river gauge cresting at 32.3 feet at 14:30 CDT on 6/27. Flood stage for this river gauge is 26.5 feet. Damage in this county from the flood was estimated at $216,950.00.

10. Jun 1, 2011Flood$150,000
    National Weather Service narrative

    Flooding along the Missouri River gradually worsened over the area during June as record releases from Gavins Point Dam brought widespread flooding along the River. The river near Blair started June around 28 feet, flood stage is 26.5 feet, and gradually climbed to a little under 33 feet by the end of the month. County roads and at least one highway and parts of Interstate 29 were flooded as were several parks and recreation areas near the river. Sand bag operations were used near Missouri Valley, Modale and Mondamin where at least 100 to 200 voluntary evacuations of residences were noted. The flooding forced the post office in Modale to move operations to a nearby town. Highway…

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

117°FJul 25, 1936

All-time low

−35°FJan 12, 1912

Warmest night

84°FJul 25, 1936

Coldest day

−17°FFeb 9, 1899

Wettest day

7.10 inAug 20, 2018

Snowiest day

15.0 inFeb 22, 1971

Hottest year

1921mean 54.2°F

Coldest year

1924mean 46.0°F

Wettest year

201548.81 in

Driest year

193613.83 in

Snowiest season

68.0 in1959-60

Station Logan 1 Wnw (USC00134894), 1,187 ft elevation, 0.9 miles from the population centre. Daily records from 1893 to October 27, 2026; 95.2% 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 USC00134894.
• 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.