A very dynamic weather situation developed over the central U.S. during the afternoon of the 4th.  A strong push of warm and moist air took place with surface dew point temperatures in the mid 60s to around 70 as far north as the southeast tip of Nebraska.  A dry line tracked east across Kansas during the day.  Behind it dew point temperatures were in the 20s and 30s.  Meanwhile, a speed maximum at the jet stream level of 145 kts was moving into the area.  The surface low associated with this system tracked across Kansas into northern Missouri during the day of the 4th into the the evening hours.  Iowa was north of the warm front.  As a result the primary severe weather associated with this system was hail.  The freezing level was around 12,000 feet MSL.  A line of thunderstorms moved into western Iowa ahead of the upper level low pressure system and its associated cold pool aloft.  These storms moved across southwest into south central and central Iowa producing widespread hail and heavy rain.  Most of the hail was in the three quarter to one inch range.  There was a report of golf ball size hail in Cass County east of Massena.  Isolated thunderstorms formed ahead of the line advancing from western Iowa.  These storms produced some spotty hail and a few reports of high winds.  Trees were toppled in Marion County in the Knoxville area for example.  Significant damage was reported to a house when large limbs fell onto the roof of the building.

Hail in CASS, IOWA
From 04-MAY-03 17:10:00 to 04-MAY-03 17:10:00 (CST)
Location: MASSENA
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in ADAIR, IOWA
From 04-MAY-03 17:45:00 to 04-MAY-03 17:45:00 (CST)
Location: GREENFIELD
Magnitude: 1.00 
Property damage: 5K
Reported by: UNKNOWN

Hail in CASS, IOWA
From 04-MAY-03 17:20:00 to 04-MAY-03 17:20:00 (CST)
Location: MASSENA
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Thunderstorm Wind in MARION, IOWA
From 04-MAY-03 17:26:00 to 04-MAY-03 17:26:00 (CST)
Location: KNOXVILLE
Magnitude: 52 EG
Property damage: 5K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in ADAMS, IOWA
From 04-MAY-03 16:55:00 to 04-MAY-03 16:55:00 (CST)
Location: CORNING
Magnitude: 52 EG
Property damage: 3K
Reported by: TRAINED SPOTTER

Hail in CASS, IOWA
From 04-MAY-03 17:00:00 to 04-MAY-03 17:00:00 (CST)
Location: WIOTA
Magnitude: 0.75 
Reported by: UNKNOWN

Hail in CASS, IOWA
From 04-MAY-03 17:07:00 to 04-MAY-03 17:07:00 (CST)
Location: CUMBERLAND
Magnitude: 0.88 
Reported by: EMERGENCY MANAGER

Hail in TAYLOR, IOWA
From 04-MAY-03 17:39:00 to 04-MAY-03 17:39:00 (CST)
Location: NEW MARKET
Magnitude: 0.75 
Reported by: UNKNOWN

Hail in CASS, IOWA
From 04-MAY-03 17:09:00 to 04-MAY-03 17:09:00 (CST)
Location: MASSENA
Magnitude: 0.75 
Reported by: EMERGENCY MANAGER

Hail in CASS, IOWA
From 04-MAY-03 16:57:00 to 04-MAY-03 16:57:00 (CST)
Location: WIOTA
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in CASS, IOWA
From 04-MAY-03 17:00:00 to 04-MAY-03 17:00:00 (CST)
Location: CUMBERLAND
Magnitude: 0.88 
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in MARION, IOWA
From 04-MAY-03 17:16:00 to 04-MAY-03 17:16:00 (CST)
Location: KNOXVILLE
Magnitude: 50 EG
Property damage: 2K
Reported by: UNKNOWN

Hail in CASS, IOWA
From 04-MAY-03 17:19:00 to 04-MAY-03 17:19:00 (CST)
Location: MASSENA
Magnitude: 0.75 
Reported by: EMERGENCY MANAGER

Hail in MADISON, IOWA
From 04-MAY-03 18:15:00 to 04-MAY-03 18:15:00 (CST)
Location: EARLHAM
Magnitude: 0.88 
Reported by: UNKNOWN

Hail in POLK, IOWA
From 04-MAY-03 19:00:00 to 04-MAY-03 19:00:00 (CST)
Location: CLIVE
Magnitude: 0.88 
Property damage: 2K
Reported by: UNKNOWN

Hail in MADISON, IOWA
From 04-MAY-03 18:14:00 to 04-MAY-03 18:14:00 (CST)
Location: MACKSBURG
Magnitude: 0.88 
Property damage: 2K
Reported by: UNKNOWN

Hail in MAHASKA, IOWA
From 04-MAY-03 17:31:00 to 04-MAY-03 17:31:00 (CST)
Location: LEIGHTON
Magnitude: 0.75 
Reported by: STORM CHASER

Hail in CASS, IOWA
From 04-MAY-03 16:42:00 to 04-MAY-03 16:42:00 (CST)
Location: ATLANTIC
Magnitude: 0.88 
Reported by: TRAINED SPOTTER

Hail in CASS, IOWA
From 04-MAY-03 16:35:00 to 04-MAY-03 16:35:00 (CST)
Location: GRISWOLD
Magnitude: 1.00 
Property damage: 5K
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in UNION, IOWA
From 04-MAY-03 17:45:00 to 04-MAY-03 17:45:00 (CST)
Location: CRESTON
Magnitude: 50 EG
Property damage: 5K
Reported by: UNKNOWN

Hail in CASS, IOWA
From 04-MAY-03 17:13:00 to 04-MAY-03 17:13:00 (CST)
Location: MASSENA
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in CASS, IOWA
From 04-MAY-03 17:15:00 to 04-MAY-03 17:15:00 (CST)
Location: MASSENA
Magnitude: 1.75 
Property damage: 5K
Reported by: UNKNOWN

Thunderstorm Wind in MARION, IOWA
From 04-MAY-03 17:31:00 to 04-MAY-03 17:31:00 (CST)
Location: KNOXVILLE
Magnitude: 52 EG
Property damage: 5K
Reported by: LAW ENFORCEMENT