Tornadoes and Flash Flooding in Iowa, May 10, 2001

Name: Tornadoes and Flash Flooding in Iowa, May 10, 2001
Start: 2001-05-10T15:09
End: 2001-05-10T23:45
Location: Iowa

May 10, 2001 · NWS DMX · 92 events in 22 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: $1.1 million
Crop damage: None recorded
Events: 92

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 cold front frontal system located to the northwest of Iowa began to sink southeast into the state during the late afternoon of the 10th. This was in fact the same cold front that set off the thunderstorm activity the previous night. The atmosphere had become quite unstable by the late afternoon with temperatures in the 80s and dew point temperature in the low to mid 60s. CAPE values were in the 2000 to 3500 J/kg range. Thunderstorms erupted during the mid afternoon hours over the north central counties of the state. These storms produced hail of one to one and one half inches in diameter. The instability of the atmosphere, combined with a favorable sheer profile, contributed to the rather quick development of tornadic supercells. The first tornado touched down in Greene County. This tornado touched down briefly and did little damage. As the afternoon progressed, the hail became larger with several reports of hail up to golf ball size from central Iowa east into the east central counties. Some of the largest hail occurred southwest of State Center in Marshall County. Baseball size hail pelted the area, causing considerable damage. One supercell produced a family of at least four tornadoes in the Grundy County area. It is very fortunate that the tornadoes from this storm did not hit within a populated area. Two of the tornadoes were fairly large. At one point, the strongest tornado was about one half mile wide based on reports from a respectable storm chaser. This tornado tracked south through eastern Grundy County and crossed into Tama County. One barn was destroyed by the larger tornado, with a house damaged by the second strong tornado. Miraculously, though the first tornado totally destroyed the barn on a farm near Conrad, none of the animals inside were injured. In fact, it was reported that the livestock appeared to be enjoying their newfound freedom as they wandered the fields at the farm. There were reports of several small tornadoes touching down in central Iowa, however they were little more than brief touchdowns. As the event progressed into the early evening hours, the thunderstorms too on a more multi-cellular structure. The large cluster of storms lost their tornadic characteristic and returned to large hail producers. Hail from three quarter inch to one and three quarter inch was common for the next several hours as the entire area moved southeast slowly. By the mid evening hours the storms began to weaken. As they did, a few reports of winds of 60 to 70 MPH were received. In addition to the wind and hail, the storms produced locally heavy rainfall. Flash flooding was also a problem with this event. The cluster of storms that dropped the tornadoes in Grundy County during the late afternoon hours caused flash flooding in the south part of the county. Rainfall near Conrad was between 2.5 and 5 inches in under two hours time. This flooded roads with some of the state roads in the south part of the county under water. The water receded fairly quickly. A merger of cells took place over Monroe County during the mid evening hours. This resulted in very heavy rainfall in the area with reports of up to 4 inches received. Flash flooding resulted with numerous roads being closed by overflowing creeks by the mid to late evening hours.

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 May 10, 2:30 PM CST, 39 minutes earlier.

Area forecast discussion, May 10, 2:30 PM CST, 39 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
330 PM CDT THU MAY 10 2001

IN THE SHORT TERM...EAST TO WEST OUTFLOW BOUNDARY ALONG HIGHWAY 20
NOW BEGINNING TO LIGHT UP WHILE ADDITIONAL DEVELOPMENT EXPECTED
FURTHER WEST ALONG COLD FRONT. ATMOSPHERE OVER SOUTHWEST IOWA SHOULD
HAVE WARMED ENOUGH TO ELIMINATE WEAK CAP SHOWN ON 18Z OMA SOUNDING.
LCL HAVE LOWERED CONSIDERABLY FROM YESTERDAY...THROUGH THEY STILL
REMAIN FAIRLY HIGH AT AROUND 5.5K FT. SURFACE WINDS IN WARM SECTOR
HAVE VEERED SO IT APPEARS MAIN THREAT FROM STORMS WILL CONTINUE TO
BE HAIL/WIND. SOME ROTATING STORMS MAY BE A LITTLE MORE LIKELY ALONG
THE OUTFLOW BOUNDARY TO THE NORTH OR NEAR OUTFLOW/FRONTAL
INTERSECTION. AS SHORT WAVE TROUGH MOVES THROUGH CWA THIS EVENING...
CONVECTION SHOULD BE SHUNTED OFF INTO N MO AND SE IA BY OR AROUND
MIDNIGHT.

MOST OF THE FRONTAL CONVECTION SHOULD BE S OF THE CWA FRIDAY SO WILL
MAINTAIN A DRY FORECAST.

MODELS SHOWING SOME POSSIBILITY OF WARM AIR ADVECTION SHOWERS/STORMS
SATURDAY. WILL HOLD OFF ON ADDITION OF POPS ACROSS THE NORTH FOR NOW
AND LET ANOTHER MODEL RUN OR TWO PASS TO GET A BETTER HANDLE ON
THAT. HAVE LEFT EXTENDEDQ UNCHANGED.

MOS TEMPS LOOK PRETTY GOOD AND ARE IN LINE WITH CURRENT FORECASTS.

.DSM...NONE

JAW

In the hours before

Special weather statement, May 10, 9:15 AM CST, 5 hours 54 minutes before

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1015 AM CDT THU MAY 10 2001

...INCREASING SEVERE WEATHER THREAT FROM 11 AM TO 4 PM IN CENTRAL
AND NORTHERN IOWA...

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.  MONITOR SHORT
TERM FORECASTS FOR ADDITIONAL FORECAST INFORMATION AS THESE
THUNDERSTORMS EVOLVE AND SPREAD SOUTHEAST THROUGH THE STATE.

IAZ004>007-015>017-023>026-033>037-044>048-111100-
BOONE-CALHOUN-CARROLL-CERRO
GORDO-CRAWFORD-EMMET-FRANKLIN-GREENE-HAMILTON-HANCOCK-HARDIN-
HUMBOLDT-KOSSUTH-PALO
ALTO-POCAHONTAS-SAC-STORY-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...AMES...BOONE...CARROLL...
DENISON...ESTHERVILLE...FORT DODGE...IOWA FALLS...MASON CITY AND
WEBSTER CITY
1015 AM CDT THU MAY 10 2001

* EVENT TIMING... 11 AM THROUGH 4 PM.

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... MODERATE
     LARGE HAIL....... MODERATE
     FLASH FLOODING... LOW

* SPOTTER ACTIVATION OUTLOOK... MODERATE

* MISCELLANEOUS INFORMATION - THUNDERSTORMS EXPANDING NORTH OF
CHEROKEE AND STORM LAKE WILL SPREAD INTO THE WESTERN PART OF THE
OUTLOOK AREA AROUND 11 AM.

IAZ027-028-038-039-049-050-057>062-070>075-111100-
ADAIR-AUDUBON-BLACK
HAWK-BREMER-BUTLER-CASS-DALLAS-GRUNDY-GUTHRIE-JASPER-MADISON-MAHASKA-
MARION-MARSHALL-POLK-POWESHIEK-TAMA-WARREN-
INCLUDING THE CITIES OF...ATLANTIC...DES MOINES...GRINNELL...
INDIANOLA...KNOXVILLE...MARSHALLTOWN...NEWTON...OSKALOOSA...PELLA...
PERRY...WATERLOO AND WAVERLY
1015 AM CDT THU MAY 10 2001

* EVENT TIMING... 1 PM TO 7 PM.

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... MODERATE
     LARGE HAIL....... MODERATE
     FLASH FLOODING... LOW

* SPOTTER ACTIVATION OUTLOOK...  MODERATE

IAZ081>086-092>097-111100-
ADAMS-APPANOOSE-CLARKE-DAVIS-DECATUR-LUCAS-MONROE-RINGGOLD-TAYLOR-
UNION-WAPELLO-WAYNE-
INCLUDING THE CITIES OF...CENTERVILLE...CHARITON...CRESTON...LAMONI
AND OTTUMWA
1015 AM CDT THU MAY 10 2001

* EVENT TIMING... 3 PM TO MIDNIGHT

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... MODERATE
     LARGE HAIL....... MODERATE
     FLASH FLOODING... MODERATE

* SPOTTER ACTIVATION OUTLOOK... MODERATE

* MISCELLANEOUS INFORMATION - THE RISK OF FLASH FLOODING WILL ALSO
INCREASE THIS EVENING AS A SECOND ROUND OF THUNDERSTORMS DEVELOPS
OVER ALREADY SATURATED GROUND.

KULA

-------------------------------------------------------------------

THREAT KEY:
    TORNADO.......... ANY TORNADO OCCURRENCE
    DAMAGING WINDS... WINDS >= 58 MPH
    LARGE HAIL....... HAIL >= 3/4 INCH DIAMETER
    FLASH FLOODING... FLOODING CAUSED BY HEAVY RAINS WITHIN 6 HOURS
                      OF RAIN EVENT. POSES THREAT TO LIFE OR
                      PROPERTY.

THREAT CATEGORY KEY:  PROBABILITY OF THREAT OCCURRING WITHIN 25
                      MILES OF POINT WITHIN FORECAST AREA
    NONE....... NOT EXPECTED.  LESS THAN 5% ( 2% FOR TORNADOES)
    LOW........ 5-15% (2-15% FOR TORNADOES)
    MODERATE... 25-35%
    HIGH....... 45% OR GREATER

SPOTTER ACTIVATION OUTLOOK KEY:
    NOT EXPECTED
    LOW........ ACTIVATION POSSIBLE BUT NOT LIKELY
    MODERATE... POSSIBILITIES ABOUT 50-50
    HIGH....... ACTIVATION LIKELY

FOR MORE INFORMATION ON PROBABILISTIC SEVERE WEATHER OUTLOOKS...GO
TO THE STORM PREDICTION CENTER WEBSITE AT
WWW.SPC.NOAA.GOV/PRODUCTS/OUTLOOK/PROBINFO.HTML .

Local storm report, May 10, 9:17 AM CST, 5 hours 52 minutes before

PRELIMINARY LOCAL STORM REPORT...CORRECTED DISTANCE
NATIONAL WEATHER SERVICE DES MOINES IA
1017 AM CDT THU MAY 10 2001

TIME(CDT)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ...3.COUNTY LOCATION....

0925 PM    6 S WEBSTER CITY          IA   1 INCH HAIL
05/09/01   HAMILTON                       REPORTED BY LAW
                                          ENFORCEMENT OFFICIAL.

Local storm report, May 10, 10:32 AM CST, 4 hours 37 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
1132 AM CDT THU MAY 10 2001

TIME(CDT)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

1129 AM    POCAHONTAS                IA   .88 INCH HAIL
05/10/01   POCAHONTAS                     REPORTED BY LAW
                                          ENFORCEMENT OFFICIAL.

Special weather statement, May 10, 11:45 AM CST, 3 hours 24 minutes before

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1245 PM CDT THU MAY 10 2001

...MORE SEVERE THUNDERSTORM DEVELOPMENT LIKELY AFTER 3 PM IN CENTRAL
AND WEST CENTRAL IOWA...

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.  MONITOR SHORT
TERM FORECASTS FOR ADDITIONAL FORECAST INFORMATION AS THESE
THUNDERSTORMS EVOLVE AND SPREAD SOUTHEAST THROUGH THE STATE.

SCATTERED MODERATE THUNDERSTORMS IN NORTH CENTRAL IOWA HAVE BEEN
WEAKENING OVER THE LAST ONE HOUR.  HOWEVER...A STRENGTHENING FRONTAL
BOUNDARY FROM NEAR WATERLOO THROUGH FORT DODGE TO BETWEEN SIOUX
CITY AND OMAHA...WILL BE THE FOCUS FOR ADDITIONAL DEVELOPMENT OF
THUNDERSTORMS AROUND MID AFTERNOON INTO THE EVENING HOURS.
CONVERGENCE OF MOISTURE WAS INCREASING OVER WESTERN IOWA AND EASTERN
NEBRASKA NEAR THIS FRONT...WITH STRONG SURFACE HEATING TAKING PLACE
SOUTH OF THE FRONT.  AN UPPER LEVEL DISTURBANCE AND JET STREAM OF
WINDS OVER NEBRASKA AND SOUTH DAKOTA WILL AID IN THUNDERSTORM
DEVELOPMENT AS WELL.  WIND AND INSTABILITY PARAMETERS INDICATE THAT
A FEW SUPERCELL THUNDERSTORMS ARE POSSIBLE...EVOLVING INTO A LINE OF
STORMS BY THIS EVENING.

IAZ004>007-015>017-023>026-033>037-044>048-111100-
BOONE-CALHOUN-CARROLL-CERRO
GORDO-CRAWFORD-EMMET-FRANKLIN-GREENE-HAMILTON-HANCOCK-HARDIN-
HUMBOLDT-KOSSUTH-PALO
ALTO-POCAHONTAS-SAC-STORY-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...AMES...BOONE...CARROLL...
DENISON...ESTHERVILLE...FORT DODGE...IOWA FALLS...MASON CITY AND
WEBSTER CITY
1245 PM CDT THU MAY 10 2001

* EVENT TIMING... NOW THROUGH 6 PM.

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... MODERATE
     LARGE HAIL....... MODERATE
     FLASH FLOODING... LOW

* SPOTTER ACTIVATION OUTLOOK... MODERATE

IAZ027-028-038-039-049-050-057>062-070>075-111100-
ADAIR-AUDUBON-BLACK
HAWK-BREMER-BUTLER-CASS-DALLAS-GRUNDY-GUTHRIE-JASPER-MADISON-MAHASKA-
MARION-MARSHALL-POLK-POWESHIEK-TAMA-WARREN-
INCLUDING THE CITIES OF...ATLANTIC...DES MOINES...GRINNELL...
INDIANOLA...KNOXVILLE...MARSHALLTOWN...NEWTON...OSKALOOSA...PELLA...
PERRY...WATERLOO AND WAVERLY
1245 PM CDT THU MAY 10 2001

* EVENT TIMING... 3 PM TO 8 PM.

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... MODERATE
     LARGE HAIL....... MODERATE
     FLASH FLOODING... LOW

* SPOTTER ACTIVATION OUTLOOK...  MODERATE

IAZ081>086-092>097-111100-
ADAMS-APPANOOSE-CLARKE-DAVIS-DECATUR-LUCAS-MONROE-RINGGOLD-TAYLOR-
UNION-WAPELLO-WAYNE-
INCLUDING THE CITIES OF...CENTERVILLE...CHARITON...CRESTON...LAMONI
AND OTTUMWA
1245 PM CDT THU MAY 10 2001

* EVENT TIMING... 3 PM TO MIDNIGHT

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... MODERATE
     LARGE HAIL....... MODERATE
     FLASH FLOODING... MODERATE

* SPOTTER ACTIVATION OUTLOOK... MODERATE

* MISCELLANEOUS INFORMATION - THE RISK OF FLASH FLOODING WILL ALSO
INCREASE THIS EVENING AS POTENTIAL THUNDERSTORM TRAINING
OCCURS OVER ALREADY SATURATED GROUND.

KULA

-------------------------------------------------------------------

THREAT KEY:
    TORNADO.......... ANY TORNADO OCCURRENCE
    DAMAGING WINDS... WINDS >= 58 MPH
    LARGE HAIL....... HAIL >= 3/4 INCH DIAMETER
    FLASH FLOODING... FLOODING CAUSED BY HEAVY RAINS WITHIN 6 HOURS
                      OF RAIN EVENT. POSES THREAT TO LIFE OR
                      PROPERTY.

THREAT CATEGORY KEY:  PROBABILITY OF THREAT OCCURRING WITHIN 25
                      MILES OF POINT WITHIN FORECAST AREA
    NONE....... NOT EXPECTED.  LESS THAN 5% ( 2% FOR TORNADOES)
    LOW........ 5-15% (2-15% FOR TORNADOES)
    MODERATE... 25-35%
    HIGH....... 45% OR GREATER

SPOTTER ACTIVATION OUTLOOK KEY:
    NOT EXPECTED
    LOW........ ACTIVATION POSSIBLE BUT NOT LIKELY
    MODERATE... POSSIBILITIES ABOUT 50-50
    HIGH....... ACTIVATION LIKELY

FOR MORE INFORMATION ON PROBABILISTIC SEVERE WEATHER OUTLOOKS...GO
TO THE STORM PREDICTION CENTER WEBSITE AT
WWW.SPC.NOAA.GOV/PRODUCTS/OUTLOOK/PROBINFO.HTML .

k

The radar

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

Open the radar archive at this moment

Event by event

75 hail, 9 tornado, 6 thunderstorm wind, 2 flash flood. Local standard time, as filed.

Hail, Hardin

When: May 10, 3:09 PM CST
Where: Hardin County, Buckeye
Measured: 1 in hail
Property damage: $5,000
Reported by: TRAINED SPOTTER
Coordinates: 42.600, -92.617

Hail, Hardin

When: May 10, 3:13 PM CST
Where: Hardin County, 5 mi N of Hubbard
Measured: 1 in hail
Property damage: $3,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.583, -92.883

Hail, Hardin

When: May 10, 3:26 PM CST
Where: Hardin County, Eldora
Measured: 1 in hail
Property damage: $5,000
Reported by: TRAINED SPOTTER
Coordinates: 42.017, -93.883

Hail, Hardin

When: May 10, 3:28 PM CST
Where: Hardin County, Eldora
Measured: 1.5 in hail
Property damage: $10,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.850, -94.433

Hail, Hardin

When: May 10, 3:30 PM CST
Where: Hardin County, 6 mi E of Eldora
Measured: 1 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 42.267, -92.483

Tornado, Greene

When: May 10, 3:37 PM CST
Where: Greene County, 3 mi SW of Grand Jct
Rating: F0
Path length: 0.2 mi
Path width: 25 yd
Property damage: $1,000
Reported by: GENERAL PUBLIC
Coordinates: 42.233, -92.517

Brief touchdown in open field

Hail, Hardin

When: May 10, 3:37 PM CST
Where: Hardin County, Eldora
Measured: 1.75 in hail
Property damage: $25,000
Reported by: BROADCAST MEDIA
Coordinates: 42.033, -93.617

Hail, Black Hawk

When: May 10, 3:39 PM CST
Where: Black Hawk County, Dunkerton
Measured: 1 in hail
Property damage: $5,000
Reported by: EMERGENCY MANAGER
Coordinates: 42.517, -92.450

Hail, Boone

When: May 10, 3:51 PM CST
Where: Boone County, Ogden
Measured: 1.75 in hail
Property damage: $20,000
Reported by: BROADCAST MEDIA
Coordinates: 41.900, -93.300

Hail, Hardin

When: May 10, 3:58 PM CST
Where: Hardin County, Eldora
Measured: 2 in hail
Property damage: $25,000
Reported by: TRAINED SPOTTER
Coordinates: 41.983, -93.217

Hail, Grundy

When: May 10, 4:00 PM CST
Where: Grundy County, Conrad
Measured: 2 in hail
Property damage: $30,000
Reported by: NEWSPAPER
Coordinates: 42.583, -92.983

Hail, Audubon

When: May 10, 4:01 PM CST
Where: Audubon County, 8 mi NE of Audubon
Measured: 1 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 41.933, -93.167

Hail, Grundy

When: May 10, 4:02 PM CST
Where: Grundy County, Beaman
Measured: 2 in hail
Property damage: $20,000
Reported by: NEWSPAPER
Coordinates: 42.567, -92.817

Hail, Butler

When: May 10, 4:02 PM CST
Where: Butler County, Kesley
Measured: 1.75 in hail
Property damage: $10,000
Reported by: OFFICIAL NWS OBS.
Coordinates: 42.217, -92.750

Tornado, Grundy

When: May 10, 4:04 PM CST to 4:07 PM CST
Where: Grundy County, 2 mi NW of Conrad
Rating: F2
Path length: 1.7 mi
Path width: 200 yd
Property damage: $150,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.817, -94.533

Most in open country. One barn hit and destroyed.

Hail, Marshall

When: May 10, 4:04 PM CST
Where: Marshall County, 4 mi N of Green Mtn
Measured: 2 in hail
Property damage: $10,000
Reported by: NEWSPAPER
Coordinates: 42.283, -92.817

Hail, Grundy

When: May 10, 4:08 PM CST
Where: Grundy County, 1 mi S of Ivester
Measured: 1 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 41.650, -94.317

Hail, Butler

When: May 10, 4:08 PM CST
Where: Butler County, 5 mi W of Aplington
Measured: 1 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 41.933, -93.183

Hail, Butler

When: May 10, 4:08 PM CST
Where: Butler County, 2 mi W of Parkersburg
Measured: 1 in hail
Property damage: $3,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.917, -93.067

Tornado, Grundy

When: May 10, 4:15 PM CST to 4:21 PM CST
Where: Grundy County, 3 mi N of Beaman
Rating: F2
Path length: 4 mi
Path width: 875 yd
Property damage: $35,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.933, -93.100

Tornado dropped down north of Beaman and progressed southeast. Crossed into Tama County from Grundy County. Most of the track was through open country.

Tornado, Grundy

When: May 10, 4:20 PM CST to 4:22 PM CST
Where: Grundy County, 2 mi NW of Conrad
Rating: F1
Path length: 1 mi
Path width: 100 yd
Property damage: $50,000
Reported by: TRAINED SPOTTER
Coordinates: 41.583, -92.850

Tornado was only on the ground briefly, but it did hit a house causing structural damage to it.

Tornado, Tama

When: May 10, 4:21 PM CST to 4:27 PM CST
Where: Tama County, 4 mi NW of Gladbrook
Rating: F2
Path length: 4 mi
Path width: 750 yd
Property damage: $35,000
Reported by: TRAINED SPOTTER
Coordinates: 41.583, -94.200

Tornado moved out of Grundy County into Tama County. Track was through mostly rural areas with limited damage.

Hail, Grundy

When: May 10, 4:25 PM CST
Where: Grundy County, 5 mi SW of Grundy Center
Measured: 1.75 in hail
Property damage: $10,000
Reported by: BROADCAST MEDIA
Coordinates: 41.333, -94.067

Tornado, Story

When: May 10, 4:27 PM CST
Where: Story County, 2 mi SW of Kelley
Rating: F0
Path length: 0.3 mi
Path width: 30 yd
Property damage: $5,000
Reported by: EMERGENCY MANAGER
Coordinates: 41.383, -93.567

Brief touchdown in open area.

Tornado, Boone

When: May 10, 4:29 PM CST to 4:35 PM CST
Where: Boone County, 4 mi E of Madrid
Rating: F1
Path length: 1 mi
Path width: 50 yd
Property damage: $5,000
Reported by: AMATEUR RADIO
Coordinates: 41.317, -94.033

Tornado tracked down during its brief life through open country.

Hail, Story

When: May 10, 4:30 PM CST
Where: Story County, Ames
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 41.267, -92.683

Thunderstorm Wind, Story

When: May 10, 4:30 PM CST
Where: Story County, Ames
Measured: 61 kt (70 mph)
Property damage: $20,000
Reported by: UNKNOWN
Coordinates: 41.350, -93.833

Flash Flood, Grundy

When: May 10, 4:30 PM CST to 6:00 PM CST
Where: Grundy County, South Portion
Property damage: $75,000
Reported by: NEWSPAPER
Coordinates: 42.317, -92.950

Hail, Butler

When: May 10, 4:34 PM CST
Where: Butler County, New Hartford
Measured: 0.88 in hail
Property damage: $4,000
Reported by: TRAINED SPOTTER
Coordinates: 41.367, -93.800

Hail, Butler

When: May 10, 4:35 PM CST
Where: Butler County, 2 mi N of New Hartford
Measured: 1 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 41.667, -93.533

Thunderstorm Wind, Butler

When: May 10, 4:37 PM CST
Where: Butler County, Aplington
Measured: 52 kt (60 mph)
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.567, -92.700

Hail, Boone

When: May 10, 4:37 PM CST
Where: Boone County, 3 mi S of Boone
Measured: 1 in hail
Property damage: $5,000
Reported by: TRAINED SPOTTER
Coordinates: 41.017, -93.317

Hail, Guthrie

When: May 10, 4:39 PM CST
Where: Guthrie County, Bagley
Measured: 1 in hail
Property damage: $4,000
Reported by: TRAINED SPOTTER
Coordinates: 41.217, -93.733

Tornado, Tama

When: May 10, 4:40 PM CST
Where: Tama County, 2 mi W of Buckingham
Rating: F0
Path length: 0.2 mi
Path width: 25 yd
Property damage: $1,000
Reported by: TRAINED SPOTTER
Coordinates: 41.200, -93.867

Brief touchdown in open country.

Tornado, Tama

When: May 10, 4:43 PM CST
Where: Tama County, 4 mi NW of Traer
Rating: F0
Path length: 0.2 mi
Path width: 25 yd
Property damage: $1,000
Reported by: TRAINED SPOTTER
Coordinates: 41.183, -93.733

Brief touchdown in open country.

Hail, Story

When: May 10, 4:44 PM CST
Where: Story County, Ames
Measured: 0.88 in hail
Property damage: $3,000
Reported by: NWS EMPLOYEE(OFF DUTY)
Coordinates: 41.217, -93.867

Hail, Black Hawk

When: May 10, 4:45 PM CST
Where: Black Hawk County, Cedar Falls
Measured: 0.88 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 41.383, -92.767

Thunderstorm Wind, Story

When: May 10, 5:10 PM CST
Where: Story County, Collins
Measured: 65 kt (75 mph)
Property damage: $20,000
Reported by: UNKNOWN
Coordinates: 41.467, -92.700

Hail, Marshall

When: May 10, 5:12 PM CST
Where: Marshall County, 4 mi SW of State Center
Measured: 2.75 in hail
Property damage: $30,000
Reported by: TRAINED SPOTTER
Coordinates: 41.067, -92.400

Hail, Marshall

When: May 10, 5:15 PM CST
Where: Marshall County, 1 mi E of Rhodes
Measured: 1.75 in hail
Property damage: $15,000
Reported by: TRAINED SPOTTER
Coordinates: 42.036, -92.999 (the zone’s center; the record gives no point)

Hail, Guthrie

When: May 10, 5:20 PM CST
Where: Guthrie County, 2 mi N of Yale
Measured: 1 in hail
Property damage: $5,000
Reported by: NWS EMPLOYEE(OFF DUTY)
Coordinates: 41.684, -94.501 (the zone’s center; the record gives no point)

Hail, Dallas

When: May 10, 5:25 PM CST
Where: Dallas County, 3 mi W of Linden
Measured: 1 in hail
Property damage: $5,000
Reported by: TRAINED SPOTTER
Coordinates: 42.233, -92.883

Hail, Marshall

When: May 10, 5:28 PM CST
Where: Marshall County, Rhodes
Measured: 1.5 in hail
Property damage: $15,000
Reported by: TRAINED SPOTTER
Coordinates: 42.233, -92.817

Hail, Marshall

When: May 10, 5:32 PM CST
Where: Marshall County, 2 mi SE of Melbourne
Measured: 0.88 in hail
Property damage: $3,000
Reported by: AMATEUR RADIO
Coordinates: 42.150, -92.817

Hail, Marshall

When: May 10, 5:36 PM CST
Where: Marshall County, Melbourne
Measured: 0.88 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 42.667, -92.917

Hail, Dallas

When: May 10, 5:37 PM CST
Where: Dallas County, Redfield
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 41.833, -94.450

Hail, Dallas

When: May 10, 5:40 PM CST
Where: Dallas County, 2 mi W of Redfield
Measured: 1.5 in hail
Property damage: $15,000
Reported by: AMATEUR RADIO
Coordinates: 41.583, -94.217

Hail, Guthrie

When: May 10, 5:43 PM CST
Where: Guthrie County, 1 mi SW of Bagley
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.250, -92.917

Hail, Dallas

When: May 10, 5:44 PM CST
Where: Dallas County, 1 mi W of Redfield
Measured: 1.75 in hail
Property damage: $20,000
Reported by: EMERGENCY MANAGER
Coordinates: 42.317, -92.833

Hail, Dallas

When: May 10, 5:45 PM CST
Where: Dallas County, Redfield
Measured: 1 in hail
Property damage: $5,000
Reported by: AMATEUR RADIO
Coordinates: 41.933, -93.717

Hail, Jasper

When: May 10, 5:52 PM CST
Where: Jasper County, 3 mi W of Newton
Measured: 1 in hail
Property damage: $5,000
Reported by: UNKNOWN
Coordinates: 41.883, -93.767

Hail, Dallas

When: May 10, 6:00 PM CST
Where: Dallas County, 2 mi SE of Adel
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.033, -93.617

Hail, Jasper

When: May 10, 6:00 PM CST
Where: Jasper County, 3 mi W of Newton
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.033, -93.617

Hail, Dallas

When: May 10, 6:07 PM CST
Where: Dallas County, Adel
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.567, -92.617

Hail, Dallas

When: May 10, 6:15 PM CST
Where: Dallas County, Waukee
Measured: 0.88 in hail
Property damage: $3,000
Reported by: EMERGENCY MANAGER
Coordinates: 41.583, -94.233

Hail, Jasper

When: May 10, 6:17 PM CST
Where: Jasper County, Reasnor
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.583, -92.533

Hail, Polk

When: May 10, 6:23 PM CST
Where: Polk County, West Des Moines
Measured: 0.88 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 41.217, -93.850

Hail, Warren

When: May 10, 6:28 PM CST
Where: Warren County, Norwalk
Measured: 0.75 in hail
Reported by: EMERGENCY MANAGER
Coordinates: 41.233, -93.917

Hail, Jasper

When: May 10, 6:29 PM CST
Where: Jasper County, 3 mi NW of Sully
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.317, -93.733

Hail, Warren

When: May 10, 6:30 PM CST
Where: Warren County, 5 mi W of Cumming
Measured: 0.75 in hail
Reported by: AMATEUR RADIO
Coordinates: 41.383, -93.267

Hail, Jasper

When: May 10, 6:36 PM CST
Where: Jasper County, Prairie City
Measured: 0.88 in hail
Property damage: $3,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.383, -93.267

Hail, Poweshiek

When: May 10, 6:37 PM CST
Where: Poweshiek County, 1 mi W of Hartwick
Measured: 0.75 in hail
Reported by: LAW ENFORCEMENT
Coordinates: 41.300, -93.650

Hail, Warren

When: May 10, 6:43 PM CST
Where: Warren County, Cumming
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.217, -93.867

Hail, Warren

When: May 10, 6:45 PM CST
Where: Warren County, Spring Hill
Measured: 0.88 in hail
Property damage: $3,000
Reported by: AMATEUR RADIO
Coordinates: 41.617, -93.900

Hail, Polk

When: May 10, 6:47 PM CST
Where: Polk County, Des Moines Arpt
Measured: 0.75 in hail
Reported by: OFFICIAL NWS OBS.
Coordinates: 41.583, -93.017

Hail, Jasper

When: May 10, 6:48 PM CST
Where: Jasper County, Sully
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 41.583, -93.717

Hail, Jasper

When: May 10, 6:50 PM CST
Where: Jasper County, Sully
Measured: 1.25 in hail
Property damage: $10,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.483, -93.683

Hail, Madison

When: May 10, 6:56 PM CST
Where: Madison County, 3 mi W of Winterset
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.617, -92.883

Hail, Warren

When: May 10, 6:58 PM CST
Where: Warren County, 1 mi N of Indianola
Measured: 0.88 in hail
Property damage: $3,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.483, -93.867

Hail, Madison

When: May 10, 6:58 PM CST
Where: Madison County, 1 mi SW of Winterset
Measured: 1 in hail
Property damage: $5,000
Reported by: AMATEUR RADIO
Coordinates: 41.600, -93.233

Hail, Mahaska

When: May 10, 7:04 PM CST
Where: Mahaska County, 3 mi SW of Oskaloosa
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 41.783, -92.367

Hail, Madison

When: May 10, 7:05 PM CST
Where: Madison County, 2 mi SW of Bevington
Measured: 0.88 in hail
Property damage: $3,000
Reported by: TRAINED SPOTTER
Coordinates: 41.483, -93.767

Hail, Madison

When: May 10, 7:09 PM CST
Where: Madison County, Bevington
Measured: 1 in hail
Property damage: $5,000
Reported by: TRAINED SPOTTER
Coordinates: 41.417, -93.667

Hail, Polk

When: May 10, 7:15 PM CST
Where: Polk County, Mitchellville
Measured: 0.75 in hail
Reported by: AMATEUR RADIO
Coordinates: 41.533, -93.667

Hail, Poweshiek

When: May 10, 7:15 PM CST
Where: Poweshiek County, 1 mi S of Searsboro
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.583, -92.850

Hail, Poweshiek

When: May 10, 7:15 PM CST
Where: Poweshiek County, Montezuma
Measured: 0.75 in hail
Reported by: LAW ENFORCEMENT
Coordinates: 41.583, -94.200

Hail, Madison

When: May 10, 7:17 PM CST
Where: Madison County, 1 mi E of Truro
Measured: 1.75 in hail
Property damage: $20,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.700, -93.100

Hail, Madison

When: May 10, 7:17 PM CST
Where: Madison County, Peru
Measured: 1.75 in hail
Property damage: $20,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.600, -93.983

Hail, Warren

When: May 10, 7:18 PM CST
Where: Warren County, St Marys
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.700, -93.100

Hail, Marion

When: May 10, 7:21 PM CST
Where: Marion County, Pleasantville
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.617, -94.017

Thunderstorm Wind, Marion

When: May 10, 7:21 PM CST
Where: Marion County, Pleasantville
Measured: 56 kt (64 mph)
Property damage: $10,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.417, -93.383

Hail, Warren

When: May 10, 7:22 PM CST
Where: Warren County, 6 mi SW of Indianola
Measured: 1 in hail
Property damage: $5,000
Reported by: TRAINED SPOTTER
Coordinates: 42.367, -93.300

Thunderstorm Wind, Madison

When: May 10, 7:23 PM CST
Where: Madison County, Truro
Measured: 52 kt (60 mph)
Property damage: $3,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.367, -93.100

Thunderstorm Wind, Lucas

When: May 10, 7:30 PM CST
Where: Lucas County, Chariton
Measured: 50 kt (58 mph)
Property damage: $2,000
Reported by: EMERGENCY MANAGER
Coordinates: 42.367, -93.100

Hail, Warren

When: May 10, 7:38 PM CST
Where: Warren County, 2 mi N of New Virginia
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.367, -92.983

Hail, Madison

When: May 10, 7:39 PM CST
Where: Madison County, 1 mi S of Truro
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.000, -94.267

Hail, Warren

When: May 10, 7:39 PM CST
Where: Warren County, New Virginia
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.367, -93.100

Hail, Madison

When: May 10, 7:39 PM CST
Where: Madison County, Truro
Measured: 1 in hail
Property damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.567, -92.167

Hail, Mahaska

When: May 10, 7:57 PM CST
Where: Mahaska County, 8 mi NW of Oskaloosa
Measured: 0.75 in hail
Reported by: LAW ENFORCEMENT
Coordinates: 42.033, -94.033

Hail, Mahaska

When: May 10, 7:57 PM CST
Where: Mahaska County, 2 mi W of New Sharon
Measured: 0.75 in hail
Reported by: LAW ENFORCEMENT
Coordinates: 42.367, -93.100

Hail, Wapello

When: May 10, 8:00 PM CST
Where: Wapello County, 3 mi N of Ottumwa
Measured: 0.75 in hail
Reported by: EMERGENCY MANAGER
Coordinates: 41.800, -94.817

Flash Flood, Monroe

When: May 10, 8:30 PM CST to 11:45 PM CST
Where: Monroe County, Countywide
Property damage: $150,000
Reported by: LAW ENFORCEMENT
Coordinates: 42.250, -92.917

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
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.
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.
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.

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, May 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: 5242054, 5242055, 5242056, 5242057, 5242058, 5242059, 5242060, 5242061, 5242062, 5242063, 5242293, 5242064, 5242294, 5242296, 5242065, 5242295, 5242066, 5242067, 5242068, 5242069, 5242163, 5242070, 5242164, 5242165, 5242166, 5242167, 5242168, 5242292, 5242169, 5242170, 5242171, 5242172, 5242173, 5242174, 5242175, 5242176, 5242177, 5242178, 5242179, 5242180, and more.