A line of thunderstorms developed north of a warm front that was slowly moving from south to north across Wisconsin.  The line of storms moved east across northern Wisconsin during the morning, producing penny to nickel size hail in Vilas County and Oneida County.  More storms developed during the afternoon as a pair of upper level disturbances passed over the state.  These storms produced large hail, wind damage, flooding rains and a tornado.
Severe storms with heavy rains, hail, high winds, and a tornado, moved across the Fox Valley and Green Bay late in the afternoon.  Highs winds blew down trees and damaged buildings at several locations.  Hail over an inch in diameter fell in Green Bay and De Pere.  Intense rains caused flooding in Green Bay.
In addition, thunderstorm winds produced a seiche on the northern shore of Lake Winnebago.  Water rose into the yards of several shoreline homes.

Hail in BROWN, WISCONSIN
From 20-AUG-10 14:32:00 to 20-AUG-10 14:32:00 (CST-6)
Location: BELLEVUE
Magnitude: 1.00 
Reported by: Trained Spotter

Hail up to quarter size fell in Bellevue.

Hail in BROWN, WISCONSIN
From 20-AUG-10 14:37:00 to 20-AUG-10 14:37:00 (CST-6)
Location: GREEN BAY
Magnitude: 1.00 
Reported by: Trained Spotter

Quarter size hail fell on the east side of Green Bay.

Hail in BROWN, WISCONSIN
From 20-AUG-10 14:38:00 to 20-AUG-10 14:38:00 (CST-6)
Location: GREEN BAY
Magnitude: 1.00 
Reported by: Amateur Radio

Quarter size hail fell, and was bouncing on the ground, at Lambeau Field in Green Bay.

Hail in CALUMET, WISCONSIN
From 20-AUG-10 15:00:00 to 20-AUG-10 15:00:00 (CST-6)
Location: DARBOY
Magnitude: 0.88 
Reported by: Trained Spotter

Nickel size hail fell at Darboy in Calumet County.

Hail in OUTAGAMIE, WISCONSIN
From 20-AUG-10 15:07:00 to 20-AUG-10 15:07:00 (CST-6)
Location: KAUKAUNA
Magnitude: 0.88 
Reported by: Trained Spotter

Hail described as grape size fell in Kaukauna.

Thunderstorm Wind in WINNEBAGO, WISCONSIN
From 20-AUG-10 14:50:00 to 20-AUG-10 14:50:00 (CST-6)
Location: NEENAH
Magnitude: 56.00 EG
Reported by: Public

Thunderstorm winds gusting to 65 mph downed trees in Neenah.

Thunderstorm Wind in BROWN, WISCONSIN
From 20-AUG-10 15:20:00 to 20-AUG-10 15:20:00 (CST-6)
Location: GREENLEAF
Magnitude: 74.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Numerous trees were uprooted and snapped in the city of Greenleaf by downburst winds from a severe thunderstorm.  A farm outbuilding was destroyed and 10 calf hutches were thrown 50 to 150 yards, killing the calves inside.

Tornado in BROWN, WISCONSIN
From 20-AUG-10 15:20:00 to 20-AUG-10 15:22:00 (CST-6)
Location: GREENLEAF
Tornado F-scale: EF1
Property damage: 100.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

The tornado touched down 2 miles southeast of Greenleaf, where several trees were snapped and uprooted.  The tornado then destroyed a relatively new barn constructed of metal wall panels and roof (DI 1, DOD 5,6).  Pieces of the wall and roof panels were strewn over 100 yards from the site.  About 50 to 100 yards on either side of the damaged barn small outbuildings and trees were untouched.  The tornado continued east-northeast to another farm and heavily damaged a metal building which contained hay bales.  Large parts of the metal roof were thrown over 200 yards.  Numerous trees along the path were snapped or uprooted.  Estimated maximum winds were 90 mph.
The tornado dissipated just north of the Holland State Wildlife Area.

Thunderstorm Wind in KEWAUNEE, WISCONSIN
From 20-AUG-10 15:40:00 to 20-AUG-10 15:40:00 (CST-6)
Location: ROSIERE
Magnitude: 56.00 EG
Reported by: Amateur Radio

Thunderstorm winds to 65 mph threw a large hay bale into a road, ripped about 20 percent of the shingles from a roof and knocked down a light pole.

Seiche in WINNEBAGO, WISCONSIN
From 20-AUG-10 17:15:00 to 20-AUG-10 17:45:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds produced a seiche on the northern shore of Lake Winnebago.  Water rose into the yards of shoreline homes.

Thunderstorm Wind in MANITOWOC, WISCONSIN
From 20-AUG-10 17:00:00 to 20-AUG-10 17:00:00 (CST-6)
Location: MANITOWOC
Magnitude: 52.00 EG
Reported by: Public

Thunderstorm wind gusts to 60 mph downed trees and tree limbs in the City of Manitowoc.  Trees were also downed in other parts of Manitowoc County.

Thunderstorm Wind in WINNEBAGO, WISCONSIN
From 20-AUG-10 17:00:00 to 20-AUG-10 17:00:00 (CST-6)
Location: OSHKOSH
Magnitude: 56.00 EG
Reported by: Trained Spotter

Numerous large tree branches and several trees were blown down by winds from a severe thunderstorm.

Seiche in CALUMET, WISCONSIN
From 20-AUG-10 17:15:00 to 20-AUG-10 17:45:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds produced a seiche on the northern shore of Lake Winnebago, affecting the Town of Harrison.  Water rose into the yards of shoreline homes.

Hail in ONEIDA, WISCONSIN
From 20-AUG-10 06:15:00 to 20-AUG-10 06:15:00 (CST-6)
Location: HAZELHURST
Magnitude: 0.88 
Reported by: Post Office

Nickel size hail fell at Hazelhurst.

Thunderstorm Wind in CALUMET, WISCONSIN
From 20-AUG-10 17:15:00 to 20-AUG-10 17:15:00 (CST-6)
Location: DARBOY
Magnitude: 52.00 EG
Reported by: Trained Spotter

Large limbs broke off trees and landed on three vehicles at a local business causing damage to all three.

Hail in ONEIDA, WISCONSIN
From 20-AUG-10 06:25:00 to 20-AUG-10 06:25:00 (CST-6)
Location: LAKE TOMAHAWK
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Penny size hail fell accompanied by torrential rain at Lake Tomahawk.

Hail in VILAS, WISCONSIN
From 20-AUG-10 09:59:00 to 20-AUG-10 09:59:00 (CST-6)
Location: LAND O LAKES
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Quarter size hail fell at Bent's Camp Resort on Mamie Lake.

Hail in BROWN, WISCONSIN
From 20-AUG-10 14:25:00 to 20-AUG-10 14:25:00 (CST-6)
Location: ALLOUEZ
Magnitude: 1.50 
Reported by: NWS Employee

Hail from penny size to ping pong ball size fell in the city of De Pere.

Thunderstorm Wind in BROWN, WISCONSIN
From 20-AUG-10 15:18:00 to 20-AUG-10 15:18:00 (CST-6)
Location: BELLEVUE
Magnitude: 54.00 MG
Reported by: Amateur Radio

A thunderstorm wind gust of 62 mph was measured at Bellevue.

Thunderstorm Wind in WINNEBAGO, WISCONSIN
From 20-AUG-10 17:40:00 to 20-AUG-10 17:40:00 (CST-6)
Location: NEENAH
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A tree and several large limbs were blown over by thunderstorm winds at Riverside Park during a concert.  Four people were taken to a hospital with non-life threatening injuries.

Thunderstorm Wind in OUTAGAMIE, WISCONSIN
From 20-AUG-10 17:26:00 to 20-AUG-10 17:26:00 (CST-6)
Location: GREENVILLE
Magnitude: 52.00 EG
Reported by: Amateur Radio

Thunderstorm winds to 60 mph downed a few trees and tree limbs in Greenville.

Thunderstorm Wind in WAUPACA, WISCONSIN
From 20-AUG-10 14:13:00 to 20-AUG-10 14:13:00 (CST-6)
Location: NEW LONDON
Magnitude: 78.00 EG
Property damage: 100.00K
Reported by: Emergency Manager

Thunderstorm winds downed more than 1,000 trees throughout New London.  A 28 foot trailer was blown onto its side and a section of the roof of the Sara Lee plant was damaged.  At least 2 homes sustained damage from fallen trees.

Flash Flood in BROWN, WISCONSIN
From 20-AUG-10 15:15:00 to 20-AUG-10 16:15:00 (CST-6)
Location: GREEN BAY
Flood cause: Heavy Rain
Property damage: 8.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Thunderstorms produced torrential rains in Green Bay.  Lombardi Avenue was closed between Oneida Street and Holmgren Way due to 3 feet of water and stalled cars on the road.  Storm and isolated sanitary sewer backups occurred in this area, causing some damage to basements.  In just 10 minutes 0.88 inch of rain fell at Austin Straubel Airport, 0.54 inch of that fell in just 4 minutes.