Thunderstorms developed over northeast Iowa Wednesday evening before tracking over east central Wisconsin overnight on May 2nd into the morning of May 3rd.  Rainfall measurements for the 24 hour period ending around 7 am CDT indicated a widespread 2 to 4.5 inches of rain over east central Wisconsin.  A roughly 15 mile wide core of higher rainfall amounts, more than 4 inches, fell from Berlin to Omro to Oshkosh to Stockbridge to Brillion to Francis Creek.
The highest reported rainfall totals in Winnebago County were 4.50 inches near Oshkosh and 3.56 inches near Omro.  Stockbridge, with 3.57 inches, and Chilton, with 3.39 inches, had the highest totals in Calumet County.  The highest totals in Manitowoc County were 3.12 inches at Francis Creek and 3.07 inches at the Manitowoc River gage.
The heavy rainfall led to flashing flooding in Winnebago County, Calumet County, and Manitowoc County that closed roads, washing out at least one, flooded basements, and caused the Manitowoc River to rapidly rise to near flood stage.  There was also some urban flooding in Outagamie County.  The storms produced hail up to nickel size, and lightning from one of the storms started a fire at a barn.  The fire destroyed the barn and killed 13 show horses.

Flash Flood in WINNEBAGO, WISCONSIN
From 03-MAY-12 00:35:00 to 03-MAY-12 10:05:00 (CST-6)
Location: WINNECONNE
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flash flooding blocked parts of USH-41 south of Oshkosh and SH-21 around Omro, causing authorities to close sections of those highways.  Approximately 75 homes sustained basement flooding.

Flash Flood in CALUMET, WISCONSIN
From 03-MAY-12 01:05:00 to 03-MAY-12 10:05:00 (CST-6)
Location: HARRISON
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flash flooding caused authorities to close many roads across Calumet County.  The Village of Hilbert sustained the worst flooding, with approximately 100 homes impacted. A flooded creek washed out a section of asphalt on Cemetery Road near Forest Junction and ripped away the culvert.  One motorist was injured while attempting to cross the missing section of road during the predawn hours.  The driver was hospitalized and the front wheels were torn from the vehicle.

Flash Flood in MANITOWOC, WISCONSIN
From 03-MAY-12 03:42:00 to 03-MAY-12 08:00:00 (CST-6)
Location: MAPLE GROVE
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flash flooding shut down access to the Town of Rockwood.  Three homes sustained basement damage from the flood.

Heavy Rain in OUTAGAMIE, WISCONSIN
From 03-MAY-12 08:00:00 to 03-MAY-12 08:50:00 (CST-6)
Location: GREENVILLE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Heavy rainfall from thunderstorms that moved through southern Outagamie County produced urban flooding in the Appleton and Grand Chute areas.

Lightning in WINNEBAGO, WISCONSIN
From 03-MAY-12 03:30:00 to 03-MAY-12 03:30:00 (CST-6)
Location: FISK
Property damage: 750.00K
Crop damage: 0.00K
Reported by: Newspaper

Lightning stuck an electrical box, starting a barn fire that destroyed the barn and a recreational vehicle, and killed 13 show horses.

Hail in OUTAGAMIE, WISCONSIN
From 03-MAY-12 08:35:00 to 03-MAY-12 08:35:00 (CST-6)
Location: APPLETON
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Penny size hail and heavy rain fell in the Town of Grand Chute, northwest of Appleton.

Hail in BROWN, WISCONSIN
From 03-MAY-12 05:15:00 to 03-MAY-12 05:15:00 (CST-6)
Location: HOWARD
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Nickel size hail fell in the Village of Howard.

Hail in WAUSHARA, WISCONSIN
From 03-MAY-12 07:20:00 to 03-MAY-12 07:20:00 (CST-6)
Location: HANCOCK
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Nickel size hail fell on the south side of Hancock.