A complex and active weather pattern was in place over the upper Midwest.  A warm front lifted north across the state during the previous day, allowing a strong surge of moisture to flow north from the Gulf of Mexico.  Temperatures rose into the 70s to low 80s as surface dew point temperatures rose into the upper 50s and 60s across the state.  By the early evening hours, a frontal boundary extended from near Sioux City east-northeast into the northeast corner of the state.  Thunderstorms fired along this front and became severe during the evening.  These storms produced very heavy rain with numerous reports of hail.  For the most part, the hail was around an inch in diameter with the storms.  There were a few reports of hail up to the size of golf balls however.  Reports of golf ball size hail were received from the Ringsted area of Emmet County, and also from the Fraser area of Boone County.   Two things were taking place during the evening.  While the thunderstorms were firing along the warm front over northern Iowa, a strong low pressure system was racing out of Colorado.  CAPE values across northeast Kansas into Iowa were in the 2000 to 3000 J/Kg range as a dry line extending south from the low approached the area.  Strong thunderstorms developed over northeast Colorado and raced east across Nebraska and Kansas.  The thunderstorms took on a bow echo configuration as they headed across the Plains at more than 60 MPH.   High winds raked Nebraska and Kansas before moving into Iowa.  There were numerous reports of winds of 60 to 80 MPH as the line advanced across the west half of Iowa with numerous reports of trees and power lines downed.  As the storms moved through Carroll County, several outbuildings were destroyed in the Templeton area.  Machine sheds were totally destroyed in Adair County by the high winds.  Further northwest, in Greene County, a barn was flattened north of Scranton.  Damage continued as the storms continued east with reports of outbuildings damaged or destroyed toward Hamilton County. One of the most damaging events of the night took place late in the storm cycle.  The storms turned into wind producers.  High winds hit the Lake Mills area in Winnebago County for example.  A barn and several sheds were destroyed by the winds around 80 MPH.   As the storms moved into Hardin County, a microburst occurred west of the Iowa Falls area with winds estimated around 85 MPH.  A tornado touched down briefly in the community of Alden, causing considerable damage in the town.  The tornado touched down in two locations of the town, damaging several buildings four blocks apart.    Concrete blocks were picked up and thrown 50 to 75 yards and roofs of the affected buildings were strewn one quarter to three eighths of a mile downstream.  One business was damages with estimated damage around $180,000.  On a farm at the edge of town damage was estimated at $100,000.  Numerous trees were downed on Highways 491 and D15, blocking travel in the area.  Shortly after this event occurred, the storms weakened and continued moving northeast.

Thunderstorm Wind in BOONE, IOWA
From 20-APR-01 23:12:00 to 20-APR-01 23:12:00 (CST)
Location: BOONE
Magnitude: 53 M
Property damage: 3K
Reported by: BROADCAST MEDIA

Hail in HAMILTON, IOWA
From 20-APR-01 23:14:00 to 20-APR-01 23:14:00 (CST)
Location: JEWELL
Magnitude: 0.88 
Property damage: 3K
Reported by: AMATEUR RADIO

Thunderstorm Wind in BOONE, IOWA
From 20-APR-01 23:15:00 to 20-APR-01 23:15:00 (CST)
Location: BOONE
Magnitude: 53 M
Property damage: 10K
Reported by: BROADCAST MEDIA

Hail in WINNEBAGO, IOWA
From 20-APR-01 23:15:00 to 20-APR-01 23:15:00 (CST)
Location: FOREST CITY
Magnitude: 1.00 
Property damage: 5K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in CRAWFORD, IOWA
From 20-APR-01 22:15:00 to 20-APR-01 22:15:00 (CST)
Location: VAIL
Magnitude: 65 E
Property damage: 30K
Reported by: NEWSPAPER

Hail in WINNEBAGO, IOWA
From 20-APR-01 23:15:00 to 20-APR-01 23:15:00 (CST)
Location: FOREST CITY
Magnitude: 1.00 
Property damage: 5K
Reported by: BROADCAST MEDIA

Hail in EMMET, IOWA
From 20-APR-01 22:39:00 to 20-APR-01 22:39:00 (CST)
Location: RINGSTED
Magnitude: 1.75 
Property damage: 10K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in GREENE, IOWA
From 20-APR-01 22:40:00 to 20-APR-01 22:40:00 (CST)
Location: SCRANTON
Magnitude: 70 M
Property damage: 50K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in GUTHRIE, IOWA
From 20-APR-01 22:44:00 to 20-APR-01 22:44:00 (CST)
Location: ADAIR
Magnitude: 57 M
Property damage: 5K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in DALLAS, IOWA
From 20-APR-01 22:53:00 to 20-APR-01 22:53:00 (CST)
Location: ADEL
Magnitude: 52 E
Property damage: 2K
Reported by: EMERGENCY MANAGER

Hail in HANCOCK, IOWA
From 20-APR-01 22:55:00 to 20-APR-01 22:55:00 (CST)
Location: CRYSTAL LAKE
Magnitude: 1.00 
Property damage: 3K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in WEBSTER, IOWA
From 20-APR-01 22:55:00 to 20-APR-01 22:55:00 (CST)
Location: GOWRIE
Magnitude: 61 E
Property damage: 5K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in HAMILTON, IOWA
From 20-APR-01 23:01:00 to 20-APR-01 23:01:00 (CST)
Location: STRATFORD
Magnitude: 70 E
Property damage: 40K
Reported by: LAW ENFORCEMENT

Hail in BOONE, IOWA
From 20-APR-01 23:05:00 to 20-APR-01 23:05:00 (CST)
Location: FRASER
Magnitude: 1.75 
Property damage: 10K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in BOONE, IOWA
From 20-APR-01 23:05:00 to 20-APR-01 23:05:00 (CST)
Location: FRASER
Magnitude: 50 E
Property damage: 2K
Reported by: LAW ENFORCEMENT

Hail in POCAHONTAS, IOWA
From 20-APR-01 21:10:00 to 20-APR-01 21:15:00 (CST)
Location: POCAHONTAS
Magnitude: 0.88 
Property damage: 3K
Reported by: TRAINED SPOTTER

Hail in POCAHONTAS, IOWA
From 20-APR-01 21:14:00 to 20-APR-01 21:14:00 (CST)
Location: ROLFE
Magnitude: 1.00 
Property damage: 5K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in GRUNDY, IOWA
From 21-APR-01 00:10:00 to 21-APR-01 00:10:00 (CST)
Location: WELLSBURG
Magnitude: 52 E
Property damage: 3K
Reported by: TRAINED SPOTTER

Tornado in HARDIN, IOWA
From 20-APR-01 23:46:00 to 20-APR-01 23:47:00 (CST)
Location: ALDEN
Tornado F-scale: F1
Property damage: 500K
Reported by: LAW ENFORCEMENT

Short touchdown within the town of Alden.

Thunderstorm Wind in CASS, IOWA
From 20-APR-01 20:56:00 to 20-APR-01 20:56:00 (CST)
Location: LEWIS
Magnitude: 50 M
Property damage: 1K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in HANCOCK, IOWA
From 20-APR-01 23:22:00 to 20-APR-01 23:22:00 (CST)
Location: CORWITH
Magnitude: 56 E
Property damage: 20K
Reported by: NEWSPAPER

Thunderstorm Wind in HAMILTON, IOWA
From 20-APR-01 23:30:00 to 20-APR-01 23:30:00 (CST)
Location: STANHOPE
Magnitude: 65 E
Property damage: 30K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in FRANKLIN, IOWA
From 20-APR-01 23:43:00 to 20-APR-01 23:43:00 (CST)
Location: LATIMER
Magnitude: 52 E
Property damage: 3K
Reported by: AMATEUR RADIO

Thunderstorm Wind in HARDIN, IOWA
From 20-APR-01 23:43:00 to 20-APR-01 23:43:00 (CST)
Location: IOWA FALLS
Magnitude: 75 E
Property damage: 100K
Reported by: EMERGENCY MANAGER

Microburst wind event.

Thunderstorm Wind in WINNEBAGO, IOWA
From 20-APR-01 23:30:00 to 20-APR-01 23:30:00 (CST)
Location: LAKE MILLS
Magnitude: 70 E
Property damage: 100K
Reported by: NEWSPAPER

Thunderstorm Wind in CARROLL, IOWA
From 20-APR-01 22:00:00 to 20-APR-01 22:00:00 (CST)
Location: MANNING
Magnitude: 65 E
Property damage: 25K
Reported by: NEWSPAPER

Thunderstorm Wind in CALHOUN, IOWA
From 20-APR-01 21:58:00 to 20-APR-01 21:58:00 (CST)
Location: LAKE CITY
Magnitude: 50 E
Property damage: 5K
Reported by: NEWSPAPER

Thunderstorm Wind in STORY, IOWA
From 20-APR-01 23:16:00 to 20-APR-01 23:16:00 (CST)
Location: AMES ARPT
Magnitude: 51 M
Property damage: 1K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in STORY, IOWA
From 20-APR-01 23:16:00 to 20-APR-01 23:16:00 (CST)
Location: AMES
Magnitude: 61 E
Property damage: 15K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in BOONE, IOWA
From 20-APR-01 23:17:00 to 20-APR-01 23:17:00 (CST)
Location: SHELDAHL
Magnitude: 52 E
Property damage: 3K
Reported by: AMATEUR RADIO

Thunderstorm Wind in STORY, IOWA
From 20-APR-01 23:18:00 to 20-APR-01 23:18:00 (CST)
Location: STORY CITY
Magnitude: 61 E
Property damage: 10K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in STORY, IOWA
From 20-APR-01 23:18:00 to 20-APR-01 23:18:00 (CST)
Location: AMES
Magnitude: 52 E
Property damage: 5K
Reported by: AMATEUR RADIO

Thunderstorm Wind in HANCOCK, IOWA
From 20-APR-01 23:18:00 to 20-APR-01 23:18:00 (CST)
Location: CORWITH
Magnitude: 70 E
Property damage: 40K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in STORY, IOWA
From 20-APR-01 23:22:00 to 20-APR-01 23:22:00 (CST)
Location: AMES
Magnitude: 52 E
Property damage: 3K
Reported by: AMATEUR RADIO

Thunderstorm Wind in CRAWFORD, IOWA
From 20-APR-01 21:55:00 to 20-APR-01 21:55:00 (CST)
Location: DENISON
Magnitude: 57 E
Property damage: 100K
Reported by: NEWSPAPER

Thunderstorm Wind in CASS, IOWA
From 20-APR-01 22:01:00 to 20-APR-01 22:01:00 (CST)
Location: GRISWOLD
Magnitude: 52 E
Property damage: 2K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in AUDUBON, IOWA
From 20-APR-01 22:04:00 to 20-APR-01 22:04:00 (CST)
Location: AUDUBON
Magnitude: 52 E
Property damage: 2K
Reported by: AMATEUR RADIO

Hail in PALO ALTO, IOWA
From 20-APR-01 22:04:00 to 20-APR-01 22:04:00 (CST)
Location: EMMETSBURG
Magnitude: 1.00 
Property damage: 5K
Reported by: BROADCAST MEDIA

Hail in HUMBOLDT, IOWA
From 20-APR-01 21:32:00 to 20-APR-01 21:32:00 (CST)
Location: HUMBOLDT
Magnitude: 0.88 
Property damage: 3K
Reported by: LAW ENFORCEMENT

Hail in HUMBOLDT, IOWA
From 20-APR-01 21:35:00 to 20-APR-01 21:35:00 (CST)
Location: HUMBOLDT
Magnitude: 0.88 
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in POCAHONTAS, IOWA
From 20-APR-01 21:43:00 to 20-APR-01 21:43:00 (CST)
Location: PLOVER
Magnitude: 1.25 
Property damage: 7K
Reported by: LAW ENFORCEMENT

Hail in POCAHONTAS, IOWA
From 20-APR-01 21:50:00 to 20-APR-01 22:00:00 (CST)
Location: POCAHONTAS
Magnitude: 1.00 
Property damage: 10K
Reported by: UNKNOWN

Thunderstorm Wind in CASS, IOWA
From 20-APR-01 21:59:00 to 20-APR-01 21:59:00 (CST)
Location: ATLANTIC
Magnitude: 52 E
Property damage: 2K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in CASS, IOWA
From 20-APR-01 22:01:00 to 20-APR-01 22:01:00 (CST)
Location: ATLANTIC
Magnitude: 71 M
Property damage: 5K
Reported by: BROADCAST MEDIA

Hail in PALO ALTO, IOWA
From 20-APR-01 22:01:00 to 20-APR-01 22:06:00 (CST)
Location: EMMETSBURG
Magnitude: 1.00 
Property damage: 5K
Reported by: LAW ENFORCEMENT

Hail in KOSSUTH, IOWA
From 20-APR-01 22:36:00 to 20-APR-01 22:36:00 (CST)
Location: BURT
Magnitude: 0.88 
Property damage: 2K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in AUDUBON, IOWA
From 20-APR-01 22:05:00 to 20-APR-01 22:05:00 (CST)
Location: AUDUBON ARPT
Magnitude: 51 M
Property damage: 1K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in CARROLL, IOWA
From 20-APR-01 22:10:00 to 20-APR-01 22:10:00 (CST)
Location: TEMPLETON
Magnitude: 68 M
Property damage: 30K
Reported by: TRAINED SPOTTER

Hail in EMMET, IOWA
From 20-APR-01 22:12:00 to 20-APR-01 22:12:00 (CST)
Location: WALLINGFORD
Magnitude: 1.00 
Property damage: 3K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in CASS, IOWA
From 20-APR-01 22:15:00 to 20-APR-01 22:15:00 (CST)
Location: ATLANTIC ARPT
Magnitude: 54 M
Property damage: 2K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in ADAIR, IOWA
From 20-APR-01 22:15:00 to 20-APR-01 22:15:00 (CST)
Location: FONTANELLE
Magnitude: 61 E
Property damage: 25K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in CARROLL, IOWA
From 20-APR-01 22:19:00 to 20-APR-01 22:19:00 (CST)
Location: CARROLL
Magnitude: 70 M
Property damage: 35K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in GREENE, IOWA
From 20-APR-01 22:23:00 to 20-APR-01 22:23:00 (CST)
Location: JEFFERSON
Magnitude: 50 E
Property damage: 1K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in ADAIR, IOWA
From 20-APR-01 22:24:00 to 20-APR-01 22:24:00 (CST)
Location: ADAIR
Magnitude: 59 M
Property damage: 3K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in CARROLL, IOWA
From 20-APR-01 22:25:00 to 20-APR-01 22:25:00 (CST)
Location: CARROLL NEU ARPT
Magnitude: 56 M
Property damage: 5K
Reported by: AMATEUR RADIO

Thunderstorm Wind in CARROLL, IOWA
From 20-APR-01 22:26:00 to 20-APR-01 22:26:00 (CST)
Location: BREDA
Magnitude: 57 M
Property damage: 5K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in GREENE, IOWA
From 20-APR-01 22:30:00 to 20-APR-01 22:30:00 (CST)
Location: JEFFERSON
Magnitude: 56 E
Property damage: 10K
Reported by: LAW ENFORCEMENT