Strong warm air advection, responsible for triggering severe thunderstorms during the morning, essentially led to a strong capping inversion during the afternoon over Eastern Iowa.  Mesoanalysis during the late afternoon showed low pressure west of Des Moines, with a warm front extending eastward across Northern Iowa into Southern Wisconsin.  Temperatures during the afternoon climbed well into the 90s and low 100s over Southwest Iowa.  The airmass was very unstable with surface based CAPE values in excess of 4000 J/Kg.  Strong shear  created a favorable environment for supercell development.  Convergence to the east of the surface low sufficiently eroded the cap by late afternoon, leading to explosive development of an isolated supercell near Waterloo.  This supercell produced a tornado in Dunkerton in Black Hawk County, which did extensive damage.  This same tornado weakened as it moved into Buchanan County.  Other weak tornadoes were spawned in Buchanan County.  There were also indications of scattered damage produced by downbursts with the second and fourth tornadoes.  Iowa governor Tom Vilsack signed a proclamation declaring Black Hawk and Buchanan Counties disaster areas.  Damage was estimated at over 1 million dollars.  Most of the damage in Buchanan County came on four farms.  The damage was spread along an eight mile stretch south of Hazelton.  Machine sheds, grain bins and outbuildings were blown apart.  Damage also occurred to farm equipment with minor damage to a few houses.

Hail in DELAWARE, IOWA
From 11-MAY-00 20:45:00 to 11-MAY-00 20:45:00 (CST)
Location: GREELEY
Magnitude: 1.75 
Reported by: EMERGENCY MANAGER

Hail in DELAWARE, IOWA
From 11-MAY-00 20:45:00 to 11-MAY-00 20:45:00 (CST)
Location: DUNDEE
Magnitude: 1.75 
Reported by: EMERGENCY MANAGER

Tornado in BUCHANAN, IOWA
From 11-MAY-00 19:45:00 to 11-MAY-00 20:03:00 (CST)
Location: HAZLETON
Tornado F-scale: F0
Property damage: 50K
Reported by: NWS STORM SURVEY

The fourth and last tornado, which was part of a family which includes the F1 event south of Hazelton, touched down 8 miles east southeast of Hazelton to 4 miles south southeast of Aurora.  It was rated an F0 with a path length of 5 1/2 miles and width of about 1/8 mile.

Funnel Cloud in DELAWARE, IOWA
From 11-MAY-00 20:45:00 to 11-MAY-00 20:45:00 (CST)
Location: MANCHESTER
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in DELAWARE, IOWA
From 11-MAY-00 21:40:00 to 11-MAY-00 21:40:00 (CST)
Location: COLESBURG
Magnitude: 61 M
Reported by: LAW ENFORCEMENT

Flood in BUCHANAN, IOWA
From 11-MAY-00 20:34:00 to 11-MAY-00 20:34:00 (CST)
Location: COUNTYWIDE
Reported by: EMERGENCY MANAGER

Tornado in BUCHANAN, IOWA
From 11-MAY-00 19:19:00 to 11-MAY-00 19:19:00 (CST)
Location: LITTLETON
Tornado F-scale: F0
Property damage: 2K
Reported by: NWS STORM SURVEY

A third tornado briefly touched down 3 miles southeast of Littleton.  It produced F0 damage mainly to trees with a path length of only about an 1/8 mile.

Thunderstorm Wind in BUCHANAN, IOWA
From 11-MAY-00 19:15:00 to 11-MAY-00 19:15:00 (CST)
Location: FAIRBANK
Magnitude: 61 M
Reported by: TRAINED SPOTTER

Tornado in BUCHANAN, IOWA
From 11-MAY-00 18:45:00 to 11-MAY-00 18:56:00 (CST)
Location: FAIRBANK
Tornado F-scale: F0
Reported by: NWS STORM SURVEY

A weak tornado, which produced no damage in Buchanan County, moved into the extreme northwest part of the county from Black Hawk County around 8 pm CDT.  The tornado was rated an F0 with an estimated path length of 2 miles.  This is likely the decaying stage of the tornado which hit Dunkerton in Black Hawk County.

Hail in BUCHANAN, IOWA
From 11-MAY-00 18:52:00 to 11-MAY-00 18:52:00 (CST)
Location: FAIRBANK
Magnitude: 1.75 
Reported by: EMERGENCY MANAGER

Tornado in BUCHANAN, IOWA
From 11-MAY-00 19:20:00 to 11-MAY-00 19:43:00 (CST)
Location: HAZLETON
Tornado F-scale: F1
Property damage: 1.5M
Reported by: NWS STORM SURVEY

A second tornado touched down 4 miles southwest of Hazelton with a continuous path for 8 miles to a point 4 miles southeast of Hazelton.  At it's maximum, it produced F1 damage with a path width of about 1000 feet.  This includes damage to major power lines and a couple of farms.  This was the strongest tornado in Buchanan County.