A warm front lifted into southern Wisconsin ahead of slow-moving low pressure in Iowa. Moderate wind shear with 0-6km shear values of 35 to 45 knots and mixed layer (ML) CAPE in the 1500 to 2500J/kg range in place over the region combined with enhanced lift from an upper disturbance rotating through the base of an approaching upper trough to produce strong to severe supercell thunderstorms during the afternoon into the evening of June 21st. The storms produced two EF1 tornadoes in the vicinity of the nearly-stationary warm front that tracked along the border between Fond Du Lac County and Green Lake County. The severe thunderstorms also produced large hail and damaging wind gusts, including a 2-mile wide microburst across sections of Waukesha County that damaged homes, barns and felled thousands of trees and numerous power lines. In addition, the thunderstorms fed off a moisture-rich air mass moving into the region, with precipitable water values around 1.8 inch, that also produced heavy rainfall and flash flooding in portions of Waukesha and Milwaukee counties.

Thunderstorm Wind in WAUKESHA, WISCONSIN
From 21-JUN-11 13:54:00 to 21-JUN-11 13:54:00 (CST-6)
Location: EAGLE
Magnitude: 69.00 MG
Reported by: Trained Spotter

Thunderstorm Wind in WAUKESHA, WISCONSIN
From 21-JUN-11 13:50:00 to 21-JUN-11 14:13:00 (CST-6)
Location: EAGLE
Magnitude: 96.00 EG
Property damage: 276.00K
Reported by: Law Enforcement

A 2-mile wide swath of damage was caused by a microburst associated with a bowing line of severe thunderstorms that tracked from southwest to northeast across a large portion of Waukesha County. Wind gusts estimated up to between 100 to 110 mph (87 to 96 knots) dropped thousands of trees, damaged homes and barns and blew down power lines that left 10,000 customers without power in Waukesha County. One person was injured by airborne tree debris near the Pewaukee and Delafield town borders. A semi-trailer truck was blown over on Interstate-94 in Waukesha County, while two other high-profile vehicles were nearly blown over by the strong winds, but concrete construction barriers saved the vehicles from being completely blown over.

Thunderstorm Wind in WAUKESHA, WISCONSIN
From 21-JUN-11 19:54:00 to 21-JUN-11 20:13:00 (CST-6)
Location: MUKWONAGO
Magnitude: 61.00 EG
Reported by: Trained Spotter

Part of a line of severe thunderstorms with damaging wind gusts up to 70 mph (60 knots) that blew down numerous trees moved through northeast and eastern Waukesha County during the middle afternoon of June 21st.

Thunderstorm Wind in WASHINGTON, WISCONSIN
From 21-JUN-11 20:33:00 to 21-JUN-11 20:33:00 (CST-6)
Location: HOLY HILL
Magnitude: 56.00 EG
Property damage: 75.00K
Reported by: Trained Spotter

Part of a line of severe thunderstorms with damaging wind gusts estimated up to 64 mph (56 knots) that blew down numerous trees and power lines moved through southern Washington County during the middle afternoon of June 21st. The powerful wind gusts blew a tree down on a house and knocked down a barn near Holy Hill.

Tornado in FOND DU LAC, WISCONSIN
From 21-JUN-11 14:21:00 to 21-JUN-11 14:31:00 (CST-6)
Location: ALTO
Tornado F-scale: EF1
Property damage: 30.00K
Reported by: NWS Storm Survey

This EF1 tornado touched down about 4.4 miles west-southwest of the town of Alto in Fond Du Lac County, on Marshview Road, about one-third of a mile north of Lake Maria Road, and tracked about 2.6 miles to the north-northwest before crossing into Green Lake County, about 3.7 miles south-southwest of Fairwater, at County Road S approximately 1/4 mile east of Schure Road. This tornado exhibited three separate damage tracks within the path, suggesting three separate vortices formed and dissipated during the life span of the tornado. The average path width was 75 yards, with a maximum path width of 105 yards. The tornado blew over trees and flattened a pole shed. The EF1 rating was determined by using DI 21(MBS) DOD5 LB to EXP with estimated winds speeds of 105 mph. The exact starting point was 43.77112/-88.88480 and the exact ending point was 43.78370/-88.88558.

Flash Flood in MILWAUKEE, WISCONSIN
From 21-JUN-11 19:30:00 to 21-JUN-11 23:00:00 (CST-6)
Location: FRANKLIN
Flood cause: Heavy Rain
Property damage: 0.50K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy downpours of rain, associated with a line of strong to severe thunderstorms that crossed southern Wisconsin during the afternoon and evening hours of June 21st, dropped between 1.5 inches and 2 inches of rain over a 1 hour to a 1 1/2 hour time period. The heavy rain caused flash flooding that covered some roads with 1 to 2 feet of water. One lane of Highway 100 in Franklin was closed due to the high water, with a vehicle stalled in water on National Avenue and the Root River Parkway in West Allis.

Flash Flood in WAUKESHA, WISCONSIN
From 21-JUN-11 19:15:00 to 21-JUN-11 23:00:00 (CST-6)
Location: MARCY
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy downpours of rain, associated with a line of strong to severe thunderstorms that crossed southern Wisconsin during the afternoon and evening hours of June 21st, dropped between 1.5 inches and 2 inches of rain over a 1 to 2 hour time period. The heavy rains caused flash flooding that covered some roads with 1 to 2 feet of water. Law enforcement officials reported the intersection of Lily Road and Burleigh Road in Brookfield, was closed, as were many other roads in the surrounding area, due to the high water covering the roadways. Some basement flooding was also reported.

Thunderstorm Wind in WALWORTH, WISCONSIN
From 21-JUN-11 19:50:00 to 21-JUN-11 19:50:00 (CST-6)
Location: EAST TROY
Magnitude: 52.00 EG
Reported by: Trained Spotter

A trained spotter reported large tree branches knocked down by thunderstorm wind gusts estimated to be as high as 60 mph (52 knots).

Hail in RACINE, WISCONSIN
From 21-JUN-11 18:03:00 to 21-JUN-11 18:03:00 (CST-6)
Location: BURLINGTON
Magnitude: 1.25 
Reported by: Trained Spotter

A trained spotter reported large hail, estimated to be 1.25 inches in diameter, that fell near a Y.M.C.A. camp east of Burlington.

Thunderstorm Wind in GREEN LAKE, WISCONSIN
From 21-JUN-11 14:28:00 to 21-JUN-11 14:28:00 (CST-6)
Location: MARKESAN
Magnitude: 50.00 EG
Reported by: Emergency Manager

The Green Lake County Emergency Manager reported trees blown down, most likely from the forward flank downdraft from the tornadic thunderstorm that moved through the extreme eastern sections of the county.

Hail in DANE, WISCONSIN
From 21-JUN-11 18:27:00 to 21-JUN-11 18:27:00 (CST-6)
Location: SUN PRAIRIE
Magnitude: 1.00 
Reported by: Trained Spotter

Tornado in GREEN LAKE, WISCONSIN
From 21-JUN-11 14:31:00 to 21-JUN-11 14:33:00 (CST-6)
Location: MARKESAN
Tornado F-scale: EF1
Property damage: 5.00K
Reported by: NWS Storm Survey

This EF1 tornado crossed into Green Lake County from Fond Du Lac County, about 4.9 miles east-southeast of Markesan, at County Road S approximately 1/4 mile east of Schure Road, and traveled a little over 2 miles to the north-northwest before dissipating approximately 3.7 miles east of Markesan, about 1200 feet northwest of the intersection of Utley Road and County Trunk Highway Q. The average path width was 75 yards, with a maximum path width of 105 yards. The tornado blew over trees and blew a door and a side panel off a pole shed. Roof shingles were also blown off of several buildings, with one home having minor roof, gutter and awning damage. The EF1 rating was determined by using DI 27(TH) DOD4 LB toward EXP with estimated winds speeds of 100 mph. The exact starting point was 43.78370/-88.88558 and the exact ending point was 43.79798/-88.91194.

Tornado in GREEN LAKE, WISCONSIN
From 21-JUN-11 14:38:00 to 21-JUN-11 14:40:00 (CST-6)
Location: GREEN LAKE
Tornado F-scale: EF1
Property damage: 2.00K
Reported by: NWS Storm Survey

This EF1 tornado entered into Green Lake County from Fond Du Lac County at Searl Road/ County Line Road about 2000 feet north of Carter Road into Green Lake County.  The average path width was 60 yards, with a maximum path width of 100 yards. The tornado uprooted trees and tore away metal panels off the roof of a pole shed. The EF1 rating was determined by using DI 21(MBS) DOD 3 EXP with estimated winds speeds of 95 mph. The exact starting point was 43.70275/-88.88517 and the exact ending point was 43.72962/-88.90737.

Tornado in FOND DU LAC, WISCONSIN
From 21-JUN-11 14:36:00 to 21-JUN-11 14:38:00 (CST-6)
Location: FAIRWATER
Tornado F-scale: EF1
Property damage: 15.00K
Reported by: NWS Storm Survey

This EF1 tornado touched down approximately 2.3 miles of northwest of Fairwater, about 200 feet southeast of the intersection of Watson Road and Searl Road/County Line Road, and traveled nearly parallel to County Line Road for almost a mile to the north-northwest before crossing County Line Road about 2000 feet north of Carter Road into Green Lake County.  The average path width was 60 yards, with a maximum path width of 100 yards. The tornado uprooted trees and tore away a wall and part of the roof of a barn. The EF1 rating was determined by using DI 1(SBO) DOD4 EXP toward UB with estimated winds speeds of 95 mph. The exact starting point was 43.66761/-88.86583 and the exact ending point was 43.70275/-88.88517.

Funnel Cloud in GREEN LAKE, WISCONSIN
From 21-JUN-11 15:14:00 to 21-JUN-11 15:14:00 (CST-6)
Location: BERLIN
Reported by: Emergency Manager

Thunderstorm Wind in JEFFERSON, WISCONSIN
From 21-JUN-11 13:45:00 to 21-JUN-11 13:45:00 (CST-6)
Location: PALMYRA
Magnitude: 56.00 EG
Reported by: NWS Employee

A National Weather Service employee reported 12 inch and larger tree limbs blown down by thunderstorm wind gusts estimated at 65 mph (56 knots).