Iowa, 2001

Flash Flooding and Hail in Iowa, May 1 to 2, 2001

May 1 to 2, 2001 · NWS DMX · 16 events in 10 counties and zones

Warm and moist air streamed into Iowa on 20 to 35 MPH surface winds from the south. By the late afternoon, temperatures over the southwest half of the state warmed into the mid 80s to around 90 with surface dew point temperatures in the low 60s.

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
1
Property damage
$508,000
Crop damage
None recorded
Events
16

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.

Warm and moist air streamed into Iowa on 20 to 35 MPH surface winds from the south. By the late afternoon, temperatures over the southwest half of the state warmed into the mid 80s to around 90 with surface dew point temperatures in the low 60s. A strong cold front was approaching from the northwest and entered the northwest counties of the state by mid afternoon. CAPE values rose rapidly as dew points rose through the 50s into the 60s. By late afternoon values were approaching 4000 J/kg just ahead of the cold front. Thunderstorms erupted along the front around 1500 CST. The storm became severe rapidly and produced hail and heavy rain in several areas. Most of the hail was one inch or less in diameter, though there was one golf ball size hail report in Carroll County later in the evening. A few reports of high winds were received, but these were quite isolated. During the mid evening into the overnight hours the line of thunderstorms became nearly stationary. Thunderstorms trained northeast along the line dumping copious amounts of rain over parts of west central into central Iowa. By midnight, two to four inches of rain had fallen in parts of Sac and Calhoun Counties. Rain continued through much of the night with amounts approaching nine inches in some areas by sunrise. Several areas of the two counties reported 7 to 10 inches of rain from the entier event. Rain began falling during the afternoon of the 1st and didn't finish until sunrise on the 2nd. A few unofficial reports indicated rainfall totals of 12 inches from the event. Flash flooding occurred with several highways reported under water. U.S. Highway 71 in Sac County was reported under water before 2200 CST. One injury occurred. Camp Creek flooded County Highway D53 east of Yetter. Several motorists drove into the water and one woman was trapped for two hours in her vehicle. She sustained injuries from being carried off the highway.

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 1, 1:15 PM CST, 2 hours 20 minutes earlier.

Area forecast discussion, May 1, 1:15 PM CST, 2 hours 20 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
215 PM CDT TUE MAY 1 2001

EARLY CONCERN WILL BE SVR WX AND DURATION OF IT.  SECOND FOCUS WILL
BE DAILY HIGH POPS AND POSSIBLE FLOODING.

MODELS HAVE BEEN ADVERTISING COLD FRONT WITH SHARP MID LVL TROF IS
NOW ENTERING THE THE STATE WITH ISOLD CELLS DVLPG ON FNT ATTM.
DESPITE LIMITED MOISTURE TO START WITH THIS AFTN POOLING NEAR THE
FNT AND INCRSG MOISTURE CONVERGENCE HAS ENHANCED CAPE AND SVR
POTENTIAL.  EXPECT TIME OF DAY HAS BIG PLAY INT YPE AS DVLPMNT UP
NORTH POINTS TO TORNADOES WHILE SRN POTENTIAL APPEARS BEST TO BE
HAIL/WIND AS SHEAR NOT THAT GREAT AND PROFLIER (SLATER) NOT AS
FAVORABLE IN SOUTH AS NRN IA NEAR WOOD LAKE PROFLIER WHICH HAS MUCH
BETTER VEERING.  LOOK AT Q/G FORCING 850/500 VEYR FAVORABLE FOR TNGT
THO SOME HINT OF SECONDARY SURGE THAT MIGHT BRING ON DVLPMNT OF
SECOND LINE OF PCPN TNGT.  THEN BOUNDARY ORIENTS E/W AND REMAINS IN
THE AREA AS S/W MOVE BY OVER NEXT SEVERAL DAYS.  KNOWING CLIMO WISE
THAT THIS IS PCPN MAX IN MAY HAVE TO KEEP EYE ON HEAVY RAINS HWVR
WILL NOT ISSUE WATCH ATTM SINCE ANTECEDENTS HAVE RISEN LAST SEVERAL
DAYS DUE TO LACK OF WIDESPREAD H.EAVY RAINS.

LOOK INTO EFP PD JUST AS UNSETTLED WITH SATURDAY ONLY DRY DAY ONYL
IF HIGH OVR MI HOLDS OFF PCPN WITH DRY ERLY FLOW OTRW WET THROUGH
THE PERIOD.

.DSM...NONE

FORSTER

In the hours before

Special weather statement, May 1, 10:40 AM CST, 4 hours 55 minutes before
CENTRAL IOWA THUNDERSTORM OUTLOOK...ADDED MISSED TIMING 2ND GROUP
NATIONAL WEATHER SERVICE DES MOINES IA
1140 AM CDT TUE MAY 1 2001

...A MODERATE RISK OF SEVERE WEATHER EXISTS LATE THIS AFTERNOON AND
EVENING IN NORTHERN AND WESTERN IOWA...

THE THREAT FOR SEVERE WEATHER AND HEAVY RAIN WILL INCREASE LATER
TODAY AS A FAST MOVING AND STRONG COLD FRONT IN EASTERN SOUTH DAKOTA
MOVES INTO WESTERN AND NORTHERN IOWA.  SOUTHERLY WINDS AHEAD OF THE
FRONT WERE BRINGING INCREASED LOW LEVEL MOISTURE INTO IOWA WITH DEW
POINTS IN THE LOWER 60S.  EXPLOSIVE THUNDERSTORM DEVELOPMENT IS
EXPECTED IN NORTHWEST IOWA ALONG THE FRONT AS TEMPERATURES REACH
INTO THE MID TO UPPER 80S.  ADEQUATE WIND SHEAR AND STRONG
INSTABILITY FAVOR THE DEVELOPMENT OF SUPERCELL THUNDERSTORMS CAPABLE
OF ALL FORMS OF SEVERE WEATHER.  THE STORMS WILL ORGANIZE INTO A
THUNDERSTORM COMPLEX STILL CAPABLE OF DAMAGING WINDS ALONG WITH
HEAVY RAIN IN CENTRAL AND SOUTHWEST IOWA THIS EVENING.  LOCALIZED
FLASH FLOODING WILL BE A THREAT WITH THE INTENSE RAINFALL RATES.

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.

IAZ004>007-015>017-023>028-033>039-044>050-057>059-070-071-021100-
ADAIR-AUDUBON-BLACK
HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-CASS-CERRO
GORDO-CRAWFORD-DALLAS-EMMET-FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-
HANCOCK-HARDIN-HUMBOLDT-KOSSUTH-MARSHALL-PALO
ALTO-POCAHONTAS-SAC-STORY-TAMA-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...AMES...ATLANTIC...BOONE...
CARROLL...DENISON...ESTHERVILLE...FORT DODGE...IOWA FALLS...
MARSHALLTOWN...MASON CITY...PERRY...WATERLOO...WAVERLY AND WEBSTER
CITY
1117 AM CDT TUE MAY 1 2001

* EVENT TIMING... 3 PM TO 9 PM.

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

* SPOTTER ACTIVATION OUTLOOK... MODERATE

* MISCELLANEOUS INFORMATION - HAIL SIZE UP TO BASEBALLS AND DAMAGING
WIND GUSTS TO 80 MPH ARE POSSIBLE.

IAZ060>062-072>075-081>086-092>097-021100-
ADAMS-APPANOOSE-CLARKE-DAVIS-DECATUR-JASPER-LUCAS-MADISON-MAHASKA-
MARION-MONROE-POLK-POWESHIEK-RINGGOLD-TAYLOR-UNION-WAPELLO-WARREN-
WAYNE-
INCLUDING THE CITIES OF...CENTERVILLE...CHARITON...CRESTON...DES
MOINES...GRINNELL...INDIANOLA...KNOXVILLE...LAMONI...NEWTON...
OSKALOOSA...OTTUMWA AND PELLA
1117 AM CDT TUE MAY 1 2001

* EVENT TIMING... 5 PM TIL MIDNIGHT

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

* SPOTTER ACTIVATION OUTLOOK... MODERATE

* MISCELLANEOUS INFORMATION - HAIL SIZE UP TO BASEBALLS AND DAMAGING
WIND GUSTS TO 80 MPH ARE POSSIBLE.

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

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 .

KULA

The radar

The Sioux Falls radar (KFSD), 172 km away, was scanning. The volume nearest the first event began at 21:36 UTC.

Open the radar archive at this moment

Event by event

12 hail, 2 thunderstorm wind, 2 flash flood. Local standard time, as filed.

Hail, Palo Alto

When
May 1, 3:35 PM CST
Where
Palo Alto County, Emmetsburg
Measured
1 in hail
Property damage
$5,000
Reported by
BROADCAST MEDIA
Coordinates
43.117, -94.700

Hail, Emmet

When
May 1, 3:40 PM CST
Where
Emmet County, Ringsted
Measured
1 in hail
Property damage
$5,000
Reported by
TRAINED SPOTTER
Coordinates
43.300, -94.517

Hail, Kossuth

When
May 1, 3:57 PM CST
Where
Kossuth County, Swea City
Measured
0.88 in hail
Property damage
$3,000
Reported by
LAW ENFORCEMENT
Coordinates
43.383, -94.300

Hail, Crawford

When
May 1, 4:07 PM CST
Where
Crawford County, Denison
Measured
1 in hail
Property damage
$7,000
Reported by
LAW ENFORCEMENT
Coordinates
42.017, -95.350

Hail, Winnebago

When
May 1, 4:10 PM CST
Where
Winnebago County, Buffalo Center
Measured
1 in hail
Property damage
$5,000
Reported by
TRAINED SPOTTER
Coordinates
43.383, -93.950

Hail, Crawford

When
May 1, 4:13 PM CST
Where
Crawford County, Denison
Measured
1 in hail
Property damage
$7,000
Reported by
BROADCAST MEDIA
Coordinates
42.017, -95.350

Hail, Crawford

When
May 1, 4:20 PM CST
Where
Crawford County, Denison
Measured
0.88 in hail
Property damage
$3,000
Reported by
TRAINED SPOTTER
Coordinates
42.017, -95.350

Thunderstorm Wind, Hamilton

When
May 1, 5:25 PM CST
Where
Hamilton County, Webster City Arpt
Measured
54 kt (62 mph)
Property damage
$2,000
Reported by
AWOS,ASOS,MESONET,ETC
Coordinates
42.433, -93.867

Hail, Carroll

When
May 1, 6:12 PM CST
Where
Carroll County, 5 mi NW of Coon Rapids
Measured
0.75 in hail
Reported by
TRAINED SPOTTER
Coordinates
41.917, -94.750

Thunderstorm Wind, Guthrie

When
May 1, 7:10 PM CST
Where
Guthrie County, 5 mi N of Guthrie Center
Measured
52 kt (60 mph)
Property damage
$1,000
Reported by
TRAINED SPOTTER
Coordinates
41.750, -94.500

Hail, Crawford

When
May 1, 7:45 PM CST
Where
Crawford County, Denison
Measured
1 in hail
Property damage
$5,000
Reported by
LAW ENFORCEMENT
Coordinates
42.017, -95.350

Hail, Carroll

When
May 1, 8:28 PM CST
Where
Carroll County, Arcadia
Measured
0.75 in hail
Reported by
LAW ENFORCEMENT
Coordinates
42.083, -95.050

Hail, Crawford

When
May 1, 8:48 PM CST
Where
Crawford County, Deloit
Measured
1 in hail
Property damage
$5,000
Reported by
LAW ENFORCEMENT
Coordinates
42.100, -95.317

Flash Flood, Sac

When
May 1, 9:30 PM CST to May 2, 3:00 AM CST
Where
Sac County, Countywide
Property damage
$200,000
Reported by
LAW ENFORCEMENT
Coordinates
42.386, -95.105 (the zone’s center; the record gives no point)

Hail, Carroll

When
May 1, 9:42 PM CST
Where
Carroll County, 4 mi E of Breda
Measured
1.75 in hail
Property damage
$10,000
Reported by
LAW ENFORCEMENT
Coordinates
42.183, -94.900

Flash Flood, Calhoun

When
May 1, 11:00 PM CST to May 2, 6:00 AM CST
Where
Calhoun County, Countywide
Injuries
1 direct, 0 indirect
Property damage
$250,000
Reported by
LAW ENFORCEMENT
Coordinates
42.385, -94.640 (the zone’s center; the record gives no point)

Injury occurred 1 E of Yetter

What these are

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.
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

More

Every storm in Iowa in 2001Every state in 2001This day in weather historyWarnings 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: 5241921, 5241922, 5241923, 5241924, 5241925, 5241926, 5241927, 5241928, 5241929, 5241930, 5241931, 5241932, 5241933, 5241934, 5241935, 5241936.