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.

Hail in WINNEBAGO, IOWA
From 01-MAY-01 16:10:00 to 01-MAY-01 16:10:00 (CST)
Location: BUFFALO CENTER
Magnitude: 1.00 
Property damage: 5K
Reported by: TRAINED SPOTTER

Flash Flood in SAC, IOWA
From 01-MAY-01 21:30:00 to 02-MAY-01 03:00:00 (CST)
Location: COUNTYWIDE
Property damage: 200K
Reported by: LAW ENFORCEMENT

Hail in PALO ALTO, IOWA
From 01-MAY-01 15:35:00 to 01-MAY-01 15:35:00 (CST)
Location: EMMETSBURG
Magnitude: 1.00 
Property damage: 5K
Reported by: BROADCAST MEDIA

Hail in CRAWFORD, IOWA
From 01-MAY-01 16:13:00 to 01-MAY-01 16:13:00 (CST)
Location: DENISON
Magnitude: 1.00 
Property damage: 7K
Reported by: BROADCAST MEDIA

Hail in CARROLL, IOWA
From 01-MAY-01 18:12:00 to 01-MAY-01 18:12:00 (CST)
Location: COON RAPIDS
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Flash Flood in CALHOUN, IOWA
From 01-MAY-01 23:00:00 to 02-MAY-01 06:00:00 (CST)
Location: COUNTYWIDE
Property damage: 250K
Reported by: LAW ENFORCEMENT

Injury occurred 1 E of Yetter

Hail in CRAWFORD, IOWA
From 01-MAY-01 20:48:00 to 01-MAY-01 20:48:00 (CST)
Location: DELOIT
Magnitude: 1.00 
Property damage: 5K
Reported by: LAW ENFORCEMENT

Hail in CRAWFORD, IOWA
From 01-MAY-01 16:07:00 to 01-MAY-01 16:07:00 (CST)
Location: DENISON
Magnitude: 1.00 
Property damage: 7K
Reported by: LAW ENFORCEMENT

Hail in KOSSUTH, IOWA
From 01-MAY-01 15:57:00 to 01-MAY-01 15:57:00 (CST)
Location: SWEA CITY
Magnitude: 0.88 
Property damage: 3K
Reported by: LAW ENFORCEMENT

Hail in CRAWFORD, IOWA
From 01-MAY-01 16:20:00 to 01-MAY-01 16:20:00 (CST)
Location: DENISON
Magnitude: 0.88 
Property damage: 3K
Reported by: TRAINED SPOTTER

Hail in CARROLL, IOWA
From 01-MAY-01 20:28:00 to 01-MAY-01 20:28:00 (CST)
Location: ARCADIA
Magnitude: 0.75 
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in GUTHRIE, IOWA
From 01-MAY-01 19:10:00 to 01-MAY-01 19:10:00 (CST)
Location: GUTHRIE CENTER
Magnitude: 52 E
Property damage: 1K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in HAMILTON, IOWA
From 01-MAY-01 17:25:00 to 01-MAY-01 17:25:00 (CST)
Location: WEBSTER CITY ARPT
Magnitude: 54 M
Property damage: 2K
Reported by: AWOS,ASOS,MESONET,ETC

Hail in EMMET, IOWA
From 01-MAY-01 15:40:00 to 01-MAY-01 15:40:00 (CST)
Location: RINGSTED
Magnitude: 1.00 
Property damage: 5K
Reported by: TRAINED SPOTTER

Hail in CARROLL, IOWA
From 01-MAY-01 21:42:00 to 01-MAY-01 21:42:00 (CST)
Location: BREDA
Magnitude: 1.75 
Property damage: 10K
Reported by: LAW ENFORCEMENT

Hail in CRAWFORD, IOWA
From 01-MAY-01 19:45:00 to 01-MAY-01 19:45:00 (CST)
Location: DENISON
Magnitude: 1.00 
Property damage: 5K
Reported by: LAW ENFORCEMENT