A cold front moved southeast slowly southeast across Iowa during the day on the 17th.  The surface front moved about half way through the state, while the front at 850 mb remained over the northwest part of the state.  The airmass was unstable, but not extremely unstable.  Lifted indices were around -2 to -5 C during the afternoon.  The convective inhibition had dropped to zero by mid afternoon with CAPE values around 1500 J/kg.  Thunderstorms erupted in the vicinity to just north of the surface cold front by late afternoon.  An MCS developed over southwest Iowa and tracked east across the state during the late afternoon and evening.  The main severe weather mode from this system was hail.  There were numerous reports of three quarter to one inch diameter hail during the period.  Some of the larger hail reached golf ball to baseball in size.  The largest hail fell in Madison County in the Winterset area as baseball size hail pummeled the area twice.  A few storms produced high winds.  One of the stronger storms was over Adams County.  In what appeared to be a macroburst, winds of around 60 MPH downed power poles and  a few outbuildings east of the Corning area.  The power poles were set on fire as they fell.  Later in the evening, over Monroe and Mahaska Counties, a thunderstorm turned into a bow echo segment and caused considerable damage near the Eddyville area.  One mile east of Eddyville on 340th St. along the Wapello-Mahaska county line was the hardest hit area.  Two farmstead received extensive damage around 9:15 p.m.  A microburst likely occurred on the farmstead located along the north side of the road (western-most farmstead), followed by a damage path spreading one-quarter mile east-southeast to a farmstead along the south side of the road.  At the southern farmstead, two farm outbuildings were destroyed.  Three poles rooted five feet into the ground were lifted complete out of the ground.  The roof of a shed was peeled back.   Pieces of the outbuildings from the northern farmstead spread out to the east and southeast up to 150 yards in width near the southern farmstead.  Length of the visible damage path was around ½ mile.  Persons in both farmsteads reported the duration of the strongest winds to be from 20 to 30 seconds.  Maximum winds were estimated to be around 85 mph.  When all was said and done, high winds flattened a barn and several outbuildings, silos, and trees.  Boards from the barn were driven through a car east of Eddyville along the southern Mahaska County border.  Several roads were blocked by fallen trees throughout the area.  Several hogs were killed when one of the barns collapsed near Eddyville.

Hail in ADAIR, IOWA
From 17-MAY-04 16:42:00 to 17-MAY-04 16:42:00 (CST)
Location: GREENFIELD
Magnitude: 1.00 
Property damage: 5K
Crop damage: 5K
Reported by: EMERGENCY MANAGER

Hail in WARREN, IOWA
From 17-MAY-04 18:51:00 to 17-MAY-04 18:51:00 (CST)
Location: ACKWORTH
Magnitude: 0.75 
Crop damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in MAHASKA, IOWA
From 17-MAY-04 20:20:00 to 17-MAY-04 20:20:00 (CST)
Location: CEDAR
Magnitude: 74 EG
Property damage: 75K
Crop damage: 10K
Reported by: FIRE DEPT/RESCUE SQUAD

Thunderstorm Wind in MAHASKA, IOWA
From 17-MAY-04 20:25:00 to 17-MAY-04 20:25:00 (CST)
Location: BEACON
Magnitude: 65 EG
Property damage: 50K
Crop damage: 5K
Reported by: FIRE DEPT/RESCUE SQUAD

Thunderstorm Wind in MAHASKA, IOWA
From 17-MAY-04 20:25:00 to 17-MAY-04 20:25:00 (CST)
Location: OSKALOOSA
Magnitude: 52 EG
Property damage: 5K
Reported by: FIRE DEPT/RESCUE SQUAD

Hail in POLK, IOWA
From 17-MAY-04 17:02:00 to 17-MAY-04 17:02:00 (CST)
Location: JOHNSTON
Magnitude: 1.00 
Property damage: 2K
Crop damage: 5K
Reported by: OFFICIAL NWS OBS.

Hail in POLK, IOWA
From 17-MAY-04 17:05:00 to 17-MAY-04 17:05:00 (CST)
Location: JOHNSTON
Magnitude: 1.00 
Property damage: 2K
Crop damage: 5K
Reported by: OFFICIAL NWS OBS.

Hail in ADAIR, IOWA
From 17-MAY-04 17:08:00 to 17-MAY-04 17:08:00 (CST)
Location: BRIDGEWATER
Magnitude: 1.00 
Property damage: 2K
Crop damage: 5K
Reported by: EMERGENCY MANAGER

Hail in ADAIR, IOWA
From 17-MAY-04 17:08:00 to 17-MAY-04 17:08:00 (CST)
Location: BRIDGEWATER
Magnitude: 1.00 
Property damage: 3K
Crop damage: 5K
Reported by: EMERGENCY MANAGER

Hail in MADISON, IOWA
From 17-MAY-04 17:12:00 to 17-MAY-04 17:12:00 (CST)
Location: EARLHAM
Magnitude: 0.75 
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 17-MAY-04 17:12:00 to 17-MAY-04 17:12:00 (CST)
Location: GRAY
Magnitude: 0.75 
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in MADISON, IOWA
From 17-MAY-04 17:46:00 to 17-MAY-04 17:46:00 (CST)
Location: EARLHAM
Magnitude: 0.75 
Crop damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in ADAMS, IOWA
From 17-MAY-04 17:53:00 to 17-MAY-04 17:53:00 (CST)
Location: CORNING
Magnitude: 52 EG
Property damage: 15K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in ADAMS, IOWA
From 17-MAY-04 17:53:00 to 17-MAY-04 17:53:00 (CST)
Location: CORNING
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in MADISON, IOWA
From 17-MAY-04 18:08:00 to 17-MAY-04 18:08:00 (CST)
Location: WINTERSET
Magnitude: 0.75 
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in MADISON, IOWA
From 17-MAY-04 18:15:00 to 17-MAY-04 18:15:00 (CST)
Location: PATTERSON
Magnitude: 1.00 
Property damage: 5K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Hail in MADISON, IOWA
From 17-MAY-04 18:25:00 to 17-MAY-04 18:25:00 (CST)
Location: WINTERSET
Magnitude: 2.75 
Property damage: 25K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in WARREN, IOWA
From 17-MAY-04 18:27:00 to 17-MAY-04 18:27:00 (CST)
Location: MARTENSDALE
Magnitude: 0.75 
Crop damage: 5K
Reported by: FIRE DEPT/RESCUE SQUAD

Hail in MADISON, IOWA
From 17-MAY-04 18:28:00 to 17-MAY-04 18:28:00 (CST)
Location: WINTERSET
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in MONROE, IOWA
From 17-MAY-04 20:25:00 to 17-MAY-04 20:25:00 (CST)
Location: ALBIA
Magnitude: 65 EG
Property damage: 10K
Crop damage: 5K
Reported by: FIRE DEPT/RESCUE SQUAD

Hail in POLK, IOWA
From 17-MAY-04 17:50:00 to 17-MAY-04 17:50:00 (CST)
Location: MITCHELLVILLE
Magnitude: 1.00 
Property damage: 3K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in CASS, IOWA
From 17-MAY-04 16:10:00 to 17-MAY-04 16:10:00 (CST)
Location: MASSENA
Magnitude: 1.25 
Property damage: 5K
Crop damage: 5K
Reported by: GENERAL PUBLIC

Thunderstorm Wind in UNION, IOWA
From 17-MAY-04 18:30:00 to 17-MAY-04 18:30:00 (CST)
Location: CRESTON
Magnitude: 50 EG
Property damage: 2K
Reported by: AMATEUR RADIO

Hail in JASPER, IOWA
From 17-MAY-04 18:38:00 to 17-MAY-04 18:38:00 (CST)
Location: PRAIRIE CITY
Magnitude: 0.75 
Crop damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in WAPELLO, IOWA
From 17-MAY-04 20:15:00 to 17-MAY-04 20:15:00 (CST)
Location: EDDYVILLE
Magnitude: 69 EG
Property damage: 50K
Reported by: NWS STORM SURVEY

Thunderstorm Wind in ADAMS, IOWA
From 17-MAY-04 18:00:00 to 17-MAY-04 18:00:00 (CST)
Location: CORNING
Magnitude: 61 EG
Property damage: 5K
Reported by: TRAINED SPOTTER

Hail in MADISON, IOWA
From 17-MAY-04 17:23:00 to 17-MAY-04 17:27:00 (CST)
Location: WINTERSET
Magnitude: 0.88 
Property damage: 2K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in MADISON, IOWA
From 17-MAY-04 17:30:00 to 17-MAY-04 17:30:00 (CST)
Location: WINTERSET
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in MADISON, IOWA
From 17-MAY-04 17:31:00 to 17-MAY-04 17:31:00 (CST)
Location: WINTERSET
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: AMATEUR RADIO

Hail in MADISON, IOWA
From 17-MAY-04 17:32:00 to 17-MAY-04 17:32:00 (CST)
Location: WINTERSET
Magnitude: 2.75 
Property damage: 25K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Hail in MADISON, IOWA
From 17-MAY-04 17:33:00 to 17-MAY-04 17:33:00 (CST)
Location: WINTERSET
Magnitude: 1.00 
Property damage: 5K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in MADISON, IOWA
From 17-MAY-04 17:33:00 to 17-MAY-04 17:33:00 (CST)
Location: WINTERSET
Magnitude: 2.75 
Property damage: 25K
Crop damage: 5K
Reported by: AMATEUR RADIO

Thunderstorm Wind in POWESHIEK, IOWA
From 17-MAY-04 17:40:00 to 17-MAY-04 17:40:00 (CST)
Location: BROOKLYN
Magnitude: 50 EG
Property damage: 1K
Reported by: TRAINED SPOTTER

Hail in POLK, IOWA
From 17-MAY-04 17:42:00 to 17-MAY-04 17:42:00 (CST)
Location: ALTOONA
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: AMATEUR RADIO

Hail in WARREN, IOWA
From 17-MAY-04 17:53:00 to 17-MAY-04 17:53:00 (CST)
Location: BEVINGTON
Magnitude: 0.75 
Crop damage: 5K
Reported by: EMERGENCY MANAGER

Hail in AUDUBON, IOWA
From 17-MAY-04 16:15:00 to 17-MAY-04 16:15:00 (CST)
Location: KIMBALLTON
Magnitude: 0.88 
Property damage: 2K
Crop damage: 5K
Reported by: AMATEUR RADIO

Hail in AUDUBON, IOWA
From 17-MAY-04 16:33:00 to 17-MAY-04 16:33:00 (CST)
Location: AUDUBON
Magnitude: 0.88 
Property damage: 3K
Crop damage: 2K
Reported by: LAW ENFORCEMENT

Hail in ADAIR, IOWA
From 17-MAY-04 16:39:00 to 17-MAY-04 16:39:00 (CST)
Location: GREENFIELD ARPT
Magnitude: 0.88 
Property damage: 2K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in MARION, IOWA
From 17-MAY-04 19:55:00 to 17-MAY-04 19:55:00 (CST)
Location: BUSSEY
Magnitude: 52 EG
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in DALLAS, IOWA
From 17-MAY-04 16:50:00 to 17-MAY-04 16:50:00 (CST)
Location: WAUKEE
Magnitude: 0.88 
Property damage: 1K
Crop damage: 5K
Reported by: GENERAL PUBLIC

Hail in POLK, IOWA
From 17-MAY-04 17:26:00 to 17-MAY-04 17:26:00 (CST)
Location: ALTOONA
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: FIRE DEPT/RESCUE SQUAD