A strong surge of moist and unstable air moved north into Iowa during the day on the 20th.  A warm front lifted north across the state during the day as a strong upper level disturbance approached from the west and northwest.  During the afternoon a cold front moved into northwest Iowa with a surface low forming along the front in that area.  Ahead of the front the airmass became unstable as dew point temperatures rose into the mid 60s to low 70s.  Thunderstorm erupted over north central Iowa during the early afternoon as colder temperatures moved in aloft, destabilizing the atmosphere.  Surface based convection developed by mid to late afternoon over the central and southern counties of the state.  The main severe weather feature with the storms was hail ranging from one to two inches in diameter.  Two inch diameter hail broke out windows in cars north of Northwood in Worth County.  Southeast of Northwood, near Silver Lake, hail nearly baseball in size caused considerable damage to property and crops.  Hail was reported to be drifted 3 to 4 inches deep in places.  Two inch diameter hail also fell in Hancock County at Garner.  The storms over southern Iowa, being surface based, had a higher likelihood of becoming tornadic.  Indeed one of the storms did produce a brief tornado touchdown in Appanoose County northwest of Udell.  The tornado did little damage as it touched down in open country.  A tornado also touched down in Lucas County north of Lucas.  The tornado struck a farmstead causing considerable damage to several buildings.  High winds about a mile north of the tornado damaged a machine shed and moved an outbuilding on a farmstead there.  The severe weather event began to change into a wind event toward the end of its life cycle.  Winds of 80 MPH were reported in Appanoose County in Udell for example.  High winds also swept through areas north of Centerville, and also north of Moulton in Appanoose County.

Hail in APPANOOSE, IOWA
From 20-SEP-01 17:49:00 to 20-SEP-01 17:49:00 (CST)
Location: UDELL
Magnitude: 1.75 
Property damage: 25K
Crop damage: 5K
Reported by: UNKNOWN

Hail in WRIGHT, IOWA
From 20-SEP-01 15:30:00 to 20-SEP-01 15:30:00 (CST)
Location: CLARION
Magnitude: 1.00 
Property damage: 5K
Crop damage: 2K
Reported by: LAW ENFORCEMENT

Tornado in APPANOOSE, IOWA
From 20-SEP-01 17:09:00 to 20-SEP-01 17:09:00 (CST)
Location: UDELL
Tornado F-scale: F1
Property damage: 5K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Tornado touched down in open country, causing little damage.

Hail in KOSSUTH, IOWA
From 20-SEP-01 13:47:00 to 20-SEP-01 13:47:00 (CST)
Location: BANCROFT
Magnitude: 1.00 
Property damage: 5K
Crop damage: 3K
Reported by: TRAINED SPOTTER

Hail in KOSSUTH, IOWA
From 20-SEP-01 13:25:00 to 20-SEP-01 13:25:00 (CST)
Location: ALGONA
Magnitude: 0.75 
Crop damage: 2K
Reported by: TRAINED SPOTTER

Hail in FRANKLIN, IOWA
From 20-SEP-01 15:30:00 to 20-SEP-01 15:30:00 (CST)
Location: SHEFFIELD
Magnitude: 1.00 
Property damage: 2K
Crop damage: 2K
Reported by: TRAINED SPOTTER

Hail in MARION, IOWA
From 20-SEP-01 16:00:00 to 20-SEP-01 16:00:00 (CST)
Location: OTLEY
Magnitude: 1.00 
Property damage: 3K
Crop damage: 3K
Reported by: TRAINED SPOTTER

Hail in WRIGHT, IOWA
From 20-SEP-01 15:17:00 to 20-SEP-01 15:17:00 (CST)
Location: GOLDFIELD
Magnitude: 1.75 
Property damage: 10K
Crop damage: 10K
Reported by: EMERGENCY MANAGER

Hail in WARREN, IOWA
From 20-SEP-01 15:39:00 to 20-SEP-01 15:39:00 (CST)
Location: MILO
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Hail in CERRO GORDO, IOWA
From 20-SEP-01 14:54:00 to 20-SEP-01 14:54:00 (CST)
Location: VENTURA
Magnitude: 0.75 
Crop damage: 1K
Reported by: TRAINED SPOTTER

Hail in BUTLER, IOWA
From 20-SEP-01 16:10:00 to 20-SEP-01 16:10:00 (CST)
Location: CLARKSVILLE
Magnitude: 0.88 
Property damage: 1K
Crop damage: 2K
Reported by: TRAINED SPOTTER

Hail in HAMILTON, IOWA
From 20-SEP-01 16:18:00 to 20-SEP-01 16:18:00 (CST)
Location: WILLIAMS
Magnitude: 1.00 
Property damage: 2K
Crop damage: 3K
Reported by: TRAINED SPOTTER

Hail in WORTH, IOWA
From 20-SEP-01 13:52:00 to 20-SEP-01 13:52:00 (CST)
Location: NORTHWOOD
Magnitude: 2.00 
Property damage: 20K
Crop damage: 10K
Reported by: TRAINED SPOTTER

Hail in KOSSUTH, IOWA
From 20-SEP-01 14:10:00 to 20-SEP-01 14:10:00 (CST)
Location: ALGONA MUNI ARPT
Magnitude: 1.75 
Property damage: 25K
Crop damage: 10K
Reported by: LAW ENFORCEMENT

Hail in WORTH, IOWA
From 20-SEP-01 14:15:00 to 20-SEP-01 14:15:00 (CST)
Location: SILVER LAKE
Magnitude: 2.50 
Property damage: 50K
Crop damage: 50K
Reported by: NEWSPAPER

Hail in BUTLER, IOWA
From 20-SEP-01 15:40:00 to 20-SEP-01 15:40:00 (CST)
Location: AREDALE
Magnitude: 0.75 
Crop damage: 2K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in APPANOOSE, IOWA
From 20-SEP-01 17:23:00 to 20-SEP-01 17:23:00 (CST)
Location: CENTERVILLE
Magnitude: 61 E
Property damage: 5K
Crop damage: 3K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in LUCAS, IOWA
From 20-SEP-01 16:32:00 to 20-SEP-01 16:32:00 (CST)
Location: LUCAS
Magnitude: 65 E
Property damage: 30K
Crop damage: 10K
Reported by: BROADCAST MEDIA

Hail in DAVIS, IOWA
From 20-SEP-01 17:57:00 to 20-SEP-01 17:57:00 (CST)
Location: BLOOMFIELD
Magnitude: 1.00 
Property damage: 5K
Crop damage: 2K
Reported by: EMERGENCY MANAGER

Hail in WORTH, IOWA
From 20-SEP-01 14:22:00 to 20-SEP-01 14:22:00 (CST)
Location: NORTHWOOD
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in HAMILTON, IOWA
From 20-SEP-01 16:21:00 to 20-SEP-01 16:21:00 (CST)
Location: WILLIAMS
Magnitude: 0.75 
Crop damage: 1K
Reported by: TRAINED SPOTTER

Hail in KOSSUTH, IOWA
From 20-SEP-01 13:38:00 to 20-SEP-01 13:38:00 (CST)
Location: ALGONA
Magnitude: 1.00 
Property damage: 3K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in KOSSUTH, IOWA
From 20-SEP-01 14:10:00 to 20-SEP-01 14:10:00 (CST)
Location: WHITTEMORE
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: BROADCAST MEDIA

Hail in WINNEBAGO, IOWA
From 20-SEP-01 14:10:00 to 20-SEP-01 14:10:00 (CST)
Location: THOMPSON
Magnitude: 1.25 
Property damage: 10K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in WORTH, IOWA
From 20-SEP-01 14:19:00 to 20-SEP-01 14:19:00 (CST)
Location: NORTHWOOD
Magnitude: 1.00 
Property damage: 5K
Crop damage: 3K
Reported by: TRAINED SPOTTER

Hail in WORTH, IOWA
From 20-SEP-01 13:57:00 to 20-SEP-01 13:57:00 (CST)
Location: SILVER LAKE
Magnitude: 1.00 
Property damage: 80K
Crop damage: 100K
Reported by: TRAINED SPOTTER

Hail in HANCOCK, IOWA
From 20-SEP-01 14:45:00 to 20-SEP-01 14:45:00 (CST)
Location: GARNER
Magnitude: 2.00 
Property damage: 25K
Crop damage: 10K
Reported by: EMERGENCY MANAGER

Hail in WARREN, IOWA
From 20-SEP-01 16:03:00 to 20-SEP-01 16:03:00 (CST)
Location: LACONA
Magnitude: 1.00 
Property damage: 5K
Crop damage: 3K
Reported by: TRAINED SPOTTER

Tornado in LUCAS, IOWA
From 20-SEP-01 16:30:00 to 20-SEP-01 16:30:00 (CST)
Location: LUCAS
Tornado F-scale: F0
Property damage: 50K
Crop damage: 5K
Reported by: NWS STORM SURVEY

Tornado caused damage to a farmstead north-northeast of Lucas.

Hail in HAMILTON, IOWA
From 20-SEP-01 16:00:00 to 20-SEP-01 16:00:00 (CST)
Location: WILLIAMS
Magnitude: 0.75 
Crop damage: 2K
Reported by: TRAINED SPOTTER

Hail in MAHASKA, IOWA
From 20-SEP-01 16:30:00 to 20-SEP-01 16:30:00 (CST)
Location: NEW SHARON
Magnitude: 0.88 
Property damage: 2K
Crop damage: 2K
Reported by: TRAINED SPOTTER

Hail in BUTLER, IOWA
From 20-SEP-01 16:12:00 to 20-SEP-01 16:12:00 (CST)
Location: ALLISON
Magnitude: 0.75 
Crop damage: 1K
Reported by: TRAINED SPOTTER

Hail in HUMBOLDT, IOWA
From 20-SEP-01 15:05:00 to 20-SEP-01 15:05:00 (CST)
Location: RENWICK
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Hail in KOSSUTH, IOWA
From 20-SEP-01 14:00:00 to 20-SEP-01 14:00:00 (CST)
Location: TITONKA
Magnitude: 1.75 
Property damage: 20K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Hail in KOSSUTH, IOWA
From 20-SEP-01 14:25:00 to 20-SEP-01 14:25:00 (CST)
Location: ALGONA
Magnitude: 1.00 
Property damage: 3K
Crop damage: 3K
Reported by: TRAINED SPOTTER

Hail in WARREN, IOWA
From 20-SEP-01 15:17:00 to 20-SEP-01 15:17:00 (CST)
Location: ST MARYS
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Hail in DAVIS, IOWA
From 20-SEP-01 17:48:00 to 20-SEP-01 17:48:00 (CST)
Location: BLOOMFIELD
Magnitude: 2.00 
Property damage: 25K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Hail in WINNEBAGO, IOWA
From 20-SEP-01 14:08:00 to 20-SEP-01 14:08:00 (CST)
Location: THOMPSON
Magnitude: 1.25 
Property damage: 2K
Crop damage: 2K
Reported by: NWS EMPLOYEE(OFF DUTY)

Hail in WARREN, IOWA
From 20-SEP-01 15:35:00 to 20-SEP-01 15:35:00 (CST)
Location: ST MARYS
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Hail in BUTLER, IOWA
From 20-SEP-01 15:53:00 to 20-SEP-01 15:53:00 (CST)
Location: ALLISON
Magnitude: 0.75 
Crop damage: 2K
Reported by: TRAINED SPOTTER

Hail in HANCOCK, IOWA
From 20-SEP-01 14:10:00 to 20-SEP-01 14:10:00 (CST)
Location: WODEN
Magnitude: 1.25 
Property damage: 5K
Crop damage: 3K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in APPANOOSE, IOWA
From 20-SEP-01 17:49:00 to 20-SEP-01 17:49:00 (CST)
Location: UDELL
Magnitude: 70 E
Property damage: 50K
Crop damage: 10K
Reported by: LAW ENFORCEMENT

Hail in DAVIS, IOWA
From 20-SEP-01 18:00:00 to 20-SEP-01 18:00:00 (CST)
Location: BLOOMFIELD
Magnitude: 0.88 
Property damage: 2K
Crop damage: 22K
Reported by: TRAINED SPOTTER

Hail in WARREN, IOWA
From 20-SEP-01 16:04:00 to 20-SEP-01 16:04:00 (CST)
Location: LACONA
Magnitude: 1.50 
Property damage: 10K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in KOSSUTH, IOWA
From 20-SEP-01 14:20:00 to 20-SEP-01 14:20:00 (CST)
Location: ALGONA
Magnitude: 1.00 
Property damage: 5K
Crop damage: 2K
Reported by: LAW ENFORCEMENT

Hail in WORTH, IOWA
From 20-SEP-01 14:28:00 to 20-SEP-01 14:28:00 (CST)
Location: NORTHWOOD
Magnitude: 1.00 
Property damage: 5K
Crop damage: 3K
Reported by: TRAINED SPOTTER

Hail in HANCOCK, IOWA
From 20-SEP-01 14:18:00 to 20-SEP-01 14:18:00 (CST)
Location: WODEN
Magnitude: 1.75 
Property damage: 15K
Crop damage: 5K
Reported by: BROADCAST MEDIA

Hail in WORTH, IOWA
From 20-SEP-01 14:18:00 to 20-SEP-01 14:18:00 (CST)
Location: NORTHWOOD
Magnitude: 1.75 
Property damage: 10K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in KOSSUTH, IOWA
From 20-SEP-01 14:10:00 to 20-SEP-01 14:10:00 (CST)
Location: TITONKA
Magnitude: 2.00 
Property damage: 15K
Crop damage: 10K
Reported by: LAW ENFORCEMENT

Hail in DAVIS, IOWA
From 20-SEP-01 18:15:00 to 20-SEP-01 18:15:00 (CST)
Location: PULASKI
Magnitude: 1.00 
Property damage: 10K
Crop damage: 15K
Reported by: NEWSPAPER

Thunderstorm Wind in APPANOOSE, IOWA
From 20-SEP-01 17:56:00 to 20-SEP-01 17:56:00 (CST)
Location: MOULTON
Magnitude: 52 E
Property damage: 5K
Reported by: LAW ENFORCEMENT