Flash Flood and Flooding in Iowa, July 21 to 22, 1998

Name: Flash Flood and Flooding in Iowa, July 21 to 22, 1998
Start: 1998-07-21T21:40
End: 1998-07-22T02:30
Location: Iowa

July 21 to 22, 1998 · NWS DMX · 8 events in 7 counties and zones

A rather complex weather situation was in place over Iowa. An outflow boundary drifted south across the state during the day from convection that had taken place earlier in the day.

Where it happened

Every event with a place to put it; 7 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: $115,000
Crop damage: $41,000
Events: 8

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS DMX wrote it up.

A rather complex weather situation was in place over Iowa. An outflow boundary drifted south across the state during the day from convection that had taken place earlier in the day. The boundary became stationary over the southern sections of the state. The airmass to the south of the boundary was extremely unstable. Thunderstorms developed explosively after sunset in a line from eastern Iowa all the way back to central Nebraska. The storms were moving east, however the line was moving only slowly southward. There was very little severe weather associated with the storms with only one report of one inch diameter hail in West Des Moines in Polk County. There were numerous reports of pea to marble size hail and 40 to 50 MPH winds however. Rainfall was very heavy with many areas receiving 2 to 3 inches in one to two hours time. This caused urban and small stream flooding in several counties along Interstate 80. The most significant flooding took place in Cass County where up to 5 inches of rain fell in less than three hours time. Flash flooding closed some highways and flooded numerous farm fields there.

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

6 flood, 1 hail, 1 flash flood. Local standard time, as filed.

Hail, Polk

When: July 21, 9:40 PM CST
Where: Polk County, West Des Moines
Measured: 1 in hail
Crop damage: $1,000
Reported by: GENERAL PUBLIC
Coordinates: 41.580, -93.720

Flash Flood, Cass

When: July 21, 10:00 PM CST to July 22, 2:00 AM CST
Where: Cass County, Atlantic
Property damage: $50,000
Crop damage: $10,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.332, -94.928 (the zone’s center; the record gives no point)

Flood, Audubon

When: July 21, 10:30 PM CST to July 22, 12:30 AM CST
Where: Audubon County, Audubon
Property damage: $10,000
Crop damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.685, -94.906 (the zone’s center; the record gives no point)

Flood, Adair

When: July 21, 10:30 PM CST to July 22, 12:30 AM CST
Where: Adair County, Adair
Property damage: $10,000
Crop damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.331, -94.471 (the zone’s center; the record gives no point)

Flood, Guthrie

When: July 21, 10:30 PM CST to July 22, 12:30 AM CST
Where: Guthrie County, Guthrie Center
Property damage: $10,000
Crop damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.684, -94.501 (the zone’s center; the record gives no point)

Flood, Polk

When: July 21, 10:30 PM CST to July 22, 1:00 AM CST
Where: Polk County, Des Moines
Property damage: $15,000
Crop damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.686, -93.573 (the zone’s center; the record gives no point)

Flood, Dallas

When: July 21, 10:30 PM CST to July 22, 1:00 AM CST
Where: Dallas County, Dallas Center
Property damage: $10,000
Crop damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.685, -94.040 (the zone’s center; the record gives no point)

Flood, Mahaska

When: July 22, 12:00 AM CST to 2:30 AM CST
Where: Mahaska County, Oskaloosa
Property damage: $10,000
Crop damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.335, -92.641 (the zone’s center; the record gives no point)

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Iowa in 1998 Every state in 1998 This day in weather history Warnings in Iowa, July 1998

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 5653376, 5653377, 5653698, 5653699, 5653700, 5653702, 5653703, 5653701.