Tornado and Flash Flood in Iowa, July 24, 2001

Name: Tornado and Flash Flood in Iowa, July 24, 2001
Start: 2001-07-24T13:00
End: 2001-07-24T19:20
Location: Iowa

July 24, 2001 · NWS DMX · 11 events in 5 counties and zones

Where it happened

Every event with a place to put it; 2 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: $367,000
Crop damage: $13,000
Events: 11

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.

Iowa continued to be in a very unstable airmass with temperatures in the 80s and dew point temperatures well into the 70s. A mesoscale vorticity maximum developed over the High Plains during the previous night and was located over northeast Nebraska during the morning of the 24th. A complex of thunderstorms continued to move east into northwest Iowa. As daytime heating continued, the storms became stronger and more organized. The main product into the early afternoon hours was heavy rainfall. During the early to mid afternoon hours, meso analysis clearly indicated the development of a surface low pressure system. As the outflow, or meso cold front, dropped southeast into southern Iowa it encountered very rich air with dew points in the low 80s. Thunderstorms developed explosively in central Iowa. Within 15 to 20 minutes of initial development the storms became severe. A tornado touched down in an open field in southern Polk County, about 5 miles south of West Des Moines. The tornado was not well organized and did little damage. Most of the storms that became severe produced high winds. Winds of 65 MPH were reported in the Waterloo area. One cell produced a wet microburst southeast of the city of Waterloo with winds around 80 MPH. The high winds ripped the roof off of a house there, resulting in the house being toppled. The storms left 2.29 inches of rain officially in the city, though some areas unofficially reported in excess of 8 inches. Considerable urban flooding took place in the city of Waterloo, with flash flooding in the outlying areas. Many basements were flooded as reports of standing water nearly 3 feet deep in the streets were received. Earlier in the afternoon heavy rains fell in Webster City. Upwards of 2 inches of rain fell in under an hour causing urban flooding in the city. The water receded quickly after the rain stopped. High winds were also reported in Story County in the Ames area. A few reports of hail were received, but the hail was not all that large being as the freezing level was 15000 feet. Nickle size hail fell in Waterloo and also in Windsor Heights. After the initial fury of activity, the storms did not produce severe weather for a few hours. As the storms continued to move east, they picked up in intensity again in the Ottumwa area. Winds of 60 to 70 MPH blew through Ottumwa and continued east toward the Agency area.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Des Moines, IA wrote its last area forecast discussion before the first event at Jul 24, 12:55 PM CST, 5 minutes earlier.

Area forecast discussion, Jul 24, 12:55 PM CST, 5 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
155 PM CDT WED JUL 24 2001

...MAIN CHALLENGES TEMPS EARLY AND PRECIP LATE IN THIS PACKAGE...

PLEASANT WEATHER ACROSS CWA AND MOST OF REGION TODAY WITH
DYING/DEPARTING MCS OVER MO AND ERN IA KEEPING THINGS COOL WITH RAIN
COOLED AIR AND PLENTY OF CLOUDS.  CONVECTIVE CLUSTER THAT OVER
CENTRAL SD STILL GOING...THOUGH IS HAS SHRUNK A BIT LAST COUPLE OF
HOURS.  NICE MOIST TONGUE APPARENT ON VIS/IR IMAGERY. SOME TURNING
TO SE NOTED LAST HOUR OR SO AND WOULD EXPECT THIS TO CONTINUE WITH
PRECIP MAINLY STAYING W OF MO RIVER.  SOME CLOUDINESS MAY EFFECT CWA
THIS EVENING THOUGH SO MAY HAVE TO USE SOME SORT OF WORDING TO THAT
EFFECT. OTHERWISE AT SFC...OUTFLOW WELL SOUTH OF STATE WITH DEEPEST
MOISTURE OVER KS/MO AND AND THE AFOREMENTIONED NARROW TONGUE INTO
CEN SD.  BEGINNINGS OF GREAT LAKES HIGH NOW SETTING UP WITH
GENERALLY SPELLS DRY AND RELATIVELY COOL CONDITIONS THIS TIME OF
YEAR.  AT UPPER LEVELS...TROPICAL MOISTURE HAS BEEN DEPRESSED SOUTH
PER VAPOR LOOP WHILE NICE VORT MAX IN SRN CA WILL PROVIDE OUR
REGIONS WEATHER FOR FRIDAY INTO SAT.

OUT OF THE MAIN THREE MODELS...NGM ACTUALLY HANDLING 18Z POSITION OF
SD TSRA...HOWEVER DONT CARE FOR MOVEMENT THEY GIVE.  WILL USE SHORT
TERM FCST TOOLS...AND AS MENTIONED ABOVE...EXPECT IT TO STAY MAINLY
WEST OF MY CWA THIS EVENING.  FARTHER OUT...MAINLY PRECIP
DIFFERENCES IN ETA/AVN ON FRI INTO SAT.  LONG WAY OUT FOR MAKING ANY
CLOSE CALLS THOUGH.  FOR TEMPS...EXPECT TO STAY AT A COMPROMISE OR
NEAR COOLER GUID FOR TEMPS DUE TO COOL...GREAT LAKES HIGH SETTING UP.

TONIGHT...AS MENTIONED...COOLER TEMPS MAY BE THE WAY TO GO NORTH.  A
LOOK AT PROGGED SFC DEWPOINT DEPRESSIONS INDICATE THERE MAY BE SOME
FOG...BUT OF GENERALLY MVFR KIND...AND PROBABLY NOT WORTH A
MENTION.  EXPECT MOSTLY CLEAR SKIES ONCE SRN IA CLOUDS EXIT LATE
THIS AFTERNOON OR EVENING.  ALSO SD/NE CONVECTION MAY THROUGH OFF
SOME CIRRUS ILL HAVE TO WORRY ABOUT.  FINALLY...LATEST 88D TRENDS
SHOWING A FEW CELLS AROUND MO/IA BORDER IN VCNTY OTM.  WILL ADJUST
WHAT I THINK WILL BE DRY ZONES AS NECESSARY AT PRESS TIME.

THUR INTO THUR NIGHT...PRETTY QUIET WITH RIDING OVER IA.  LITTLE TO
DISCUSS HERE UNTIL LATE THURS NIGHT AS POSITIVE THETA E ADVECTION
AND WAA KICK IN IN FAR WRN CWA AND WEST.  ALREADY HAVE A GOING 30
POP OUT WEST AND WILL KEEP.  WITH GREAT LAKES HIGH IN PLACE...WILL
HAVE A /VERY/ TOUGH TIME MAKING IT TOO FAR EAST.  TEMPS WILL
CONTINUE ON COOL SIDE.

FRIDAY INTO FRIDAY NIGHT AND SAT...CURRENT SW CA SYSTEM BEGINS TO
EFFECT PLAINS INTO IA/MO.  WILL SLOWLY BRING POPS EAST...SOMEWHAT IN
LINE WITH CURRENT ZFP.  FRIDAY WILL STAY DRY EAST...UNTIL VERY LATE
IN THE AFTERNOON AT THE EARLIEST. MAV NOW LOOKS TOO COOL AND WILL
USE FWC.  LINGERING CONVECTION SAT NIGHT MORNING WHICH IS A BIT
FASTER THAN CURRENT ZFP.

FOR THE EXTENDED...LOOKS LIKE SRN PLAINS RIDGE EXPANDS A BIT...BUT
IA STAYS IN CLOSE PROXIMITY TO NW SIDE OF RIDGE...PERHAPS KEEPING
MCS THREAT GOING.  THIS MATCHES CURRENT EXTENDED.  MAINLY SEASONABLE
TEMPS.

.DSM...NONE

SEARCY

The radar

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

Open the radar archive at this moment

Event by event

6 thunderstorm wind, 2 hail, 1 flood, 1 flash flood, 1 tornado. Local standard time, as filed.

Flood, Hamilton

When: July 24, 1:00 PM CST to 3:00 PM CST
Where: Hamilton County, Webster City
Property damage: $25,000
Reported by: NEWSPAPER
Coordinates: 42.384, -93.707 (the zone’s center; the record gives no point)

Flash Flood, Black Hawk

When: July 24, 3:00 PM CST to 5:00 PM CST
Where: Black Hawk County, Waterloo
Property damage: $250,000
Reported by: NEWSPAPER
Coordinates: 42.470, -92.309 (the zone’s center; the record gives no point)

Hail, Black Hawk

When: July 24, 3:08 PM CST
Where: Black Hawk County, Waterloo
Measured: 0.88 in hail
Property damage: $3,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.500, -92.350

Thunderstorm Wind, Black Hawk

When: July 24, 3:13 PM CST
Where: Black Hawk County, Elk Run Hgts
Measured: 57 kt (66 mph)
Property damage: $10,000
Reported by: BROADCAST MEDIA
Coordinates: 42.467, -92.267

Thunderstorm Wind, Story

When: July 24, 3:15 PM CST
Where: Story County, Ames
Measured: 52 kt (60 mph)
Property damage: $3,000
Reported by: AMATEUR RADIO
Coordinates: 42.033, -93.617

Thunderstorm Wind, Black Hawk

When: July 24, 3:20 PM CST
Where: Black Hawk County, 5 mi SE of Waterloo
Measured: 69 kt (79 mph)
Property damage: $50,000
Crop damage: $10,000
Reported by: BROADCAST MEDIA
Coordinates: 42.450, -92.283

Thunderstorm Wind, Story

When: July 24, 3:35 PM CST
Where: Story County, Ames
Measured: 52 kt (60 mph)
Property damage: $10,000
Reported by: EMERGENCY MANAGER
Coordinates: 42.033, -93.617

Tornado, Polk

When: July 24, 3:36 PM CST
Where: Polk County, 5 mi S of West Des Moines
Rating: F0
Path length: 0.2 mi
Path width: 25 yd
Crop damage: $1,000
Reported by: AMATEUR RADIO
Coordinates: 41.517, -93.717

Brief touchdown in field south of town.

Hail, Polk

When: July 24, 3:36 PM CST
Where: Polk County, Windsor Hgts
Measured: 0.88 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 41.600, -93.717

Thunderstorm Wind, Wapello

When: July 24, 6:36 PM CST
Where: Wapello County, Ottumwa Arpt
Measured: 54 kt (62 mph)
Property damage: $3,000
Reported by: AWOS,ASOS,MESONET,ETC
Coordinates: 41.100, -92.450

Thunderstorm Wind, Wapello

When: July 24, 7:20 PM CST
Where: Wapello County, 2 mi N of Agency
Measured: 61 kt (70 mph)
Property damage: $10,000
Crop damage: $2,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.017, -92.367

What these are

Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
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.
Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.
Tornado: A violently rotating column of air in contact with the ground and extending from a thunderstorm, filed with its path, width and Fujita or Enhanced Fujita rating from the damage survey.

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

The same day elsewhere

Every storm in Iowa in 2001 Every state in 2001 This day in weather history The tornado archive for Iowa, 2001 Warnings in Iowa, July 2001

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: 5252389, 5252388, 5252293, 5252294, 5252295, 5252296, 5252297, 5252384, 5252385, 5252386, 5252387.