A cold front moved southeast across the state during the day on the 21st.  The airmass was moderately unstable with CAPE values ahead of the front around 2000 J/kg and lifted indices of -3 to -6 C.  Downdraft CAPE was between 800 and 1000 J/kg, with 500 J/kg of CAPE available in the -10 to -30 C layer of the atmosphere.  Precipitable water values increased to between 1.5 and 2 inches.  Sufficient shear was available with about 40 kts of shear.  The freezing level was quite high, around 14,000 feet.  A line of thunderstorms ahead of the cold front intensified around mid day.  The storms continued to track east across the state during the afternoon.  One of the storms produced high winds in the Sully area of Jasper County.  The air exchanger and part of the roof was torn off the gym building of the Sully school.  One of the storms produced one and one half inch diameter hail in Guthrie County, causing damage to buildings and vehicles there.  The storms produced heavy rainfall in south central Iowa, with reports of 2 to 3.5 inches in a short time received.  Flash flooding occurred in Decatur County with rushing water reported over the roads north of Pleasanton.  A county road was washed out in southern Decatur County in Morgan Township.  As the thunderstorms moved through Tama County, lightning struck a house in Traer, setting it on fire.  Minor damage occurred.

Heavy Rain in DECATUR, IOWA
From 21-SEP-10 13:52:00 to 21-SEP-10 15:52:00 (CST-6)
Location: DAVIS CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter measured 3.2 inches of rain.

Heavy Rain in WAYNE, IOWA
From 21-SEP-10 14:30:00 to 21-SEP-10 16:02:00 (CST-6)
Location: SEYMOUR
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Two inches of rain had fallen since 1430 CST with 3-4 inches of water flowing pretty quickly across County Road 230th just northwest of Seymour.

Flash Flood in DECATUR, IOWA
From 21-SEP-10 17:00:00 to 21-SEP-10 20:50:00 (CST-6)
Location: PLEASANTON
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 5.00K
Reported by: Law Enforcement

Law enforcement relayed that 290th Ave was washed out in Morgan Township, Section 5.

Hail in GUTHRIE, IOWA
From 21-SEP-10 07:53:00 to 21-SEP-10 07:53:00 (CST-6)
Location: BAGLEY
Magnitude: 1.50 
Property damage: 10.00K
Crop damage: 25.00K
Reported by: Law Enforcement

Both vehicles at a house received considerable hail damage.

Lightning in TAMA, IOWA
From 21-SEP-10 10:05:00 to 21-SEP-10 10:05:00 (CST-6)
Location: TRAER
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorm Wind in JASPER, IOWA
From 21-SEP-10 11:55:00 to 21-SEP-10 11:55:00 (CST-6)
Location: SULLY
Magnitude: 74.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Broadcast Media

An air exchanger on the rooftop was ripped off.  Around one quarter of the roof of the gym of the Lynnville-Sully school was peeled back with a section of the roof thrown 50 to 100 feet to the east of the building, causing some tree damage.  One window was blown out.

Flash Flood in DECATUR, IOWA
From 21-SEP-10 15:52:00 to 21-SEP-10 20:50:00 (CST-6)
Location: PLEASANTON
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter reported water rushing over Quarry Road near R46 with water too deep to cross.  The Little River was out of its banks in a few areas.