Severe thunderstorms developed across northeast Wisconsin as a weak surface boundary encountered an unstable air mass.  The storms produced winds estimated as high as 100 mph and hail to golf ball size, causing millions of dollars in damage, power outages to thousands and injuring one person.

Thunderstorm Wind in MARATHON, WISCONSIN
From 20-JUL-10 15:20:00 to 20-JUL-10 15:20:00 (CST-6)
Location: TAEGESVILLE
Magnitude: 83.00 EG
Reported by: Amateur Radio

Over 200 pine trees were snapped or uprooted just east of Little Chicago by a powerful downburst.  Some of the trees and part of a grain storage unit were blown onto a nearby road.

Thunderstorm Wind in MARATHON, WISCONSIN
From 20-JUL-10 15:40:00 to 20-JUL-10 15:40:00 (CST-6)
Location: WAUSAU
Magnitude: 56.00 EG
Reported by: Trained Spotter

Thunderstorm winds downed 1 to 2 foot diameter trees at Northcentral Technical College in Wausau.

Thunderstorm Wind in SHAWANO, WISCONSIN
From 20-JUL-10 16:17:00 to 20-JUL-10 16:17:00 (CST-6)
Location: WITTENBERG
Magnitude: 78.00 EG
Property damage: 50.00K
Reported by: Emergency Manager

Thunderstorm winds downed or snapped numerous trees and downed power lines throughout Wittenburg.  The Wittenberg-Birnamwood High School had about 75 feet of its rubber membrane roof and underlying foam insulation peeled from the west side of the gymnasium.  Several large pine trees along the south side of the school were uprooted.  A camper trailer was blown from its support pad and rolled about 40 feet before resting on its roof.  Two of the three pools at the water treatment plant had portions of their plastic thermal covers blown off.  Downed trees blocked State Highway 45 causing authorities to close the road for several hours.  More than 140 homes were damaged, but damage to most of the homes was minor.

Thunderstorm Wind in SHAWANO, WISCONSIN
From 20-JUL-10 16:57:00 to 20-JUL-10 16:57:00 (CST-6)
Location: BELLE PLAINE
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorm winds downed a tree which struck a woman in the town of Belle Plaine.  The injury was non-life threatening.

Hail in OUTAGAMIE, WISCONSIN
From 20-JUL-10 18:28:00 to 20-JUL-10 18:28:00 (CST-6)
Location: APPLETON
Magnitude: 1.75 
Property damage: 6.20M
Reported by: Insurance Company

Golf ball size hail near Appleton damaged nearly 1,000 vehicles and at least 200 homes.  Many of the homes sustained significant damage as the hail damaged roofs and siding.

Hail in WINNEBAGO, WISCONSIN
From 20-JUL-10 18:32:00 to 20-JUL-10 18:32:00 (CST-6)
Location: MENASHA
Magnitude: 1.75 
Property damage: 9.00M
Reported by: Insurance Company

Hail, up to golf ball size, damaged hundreds of vehicles and more than 200 homes in northeast Winnebago County.  The wind-driven hail caused significant damage to roofs and siding.

Hail in CALUMET, WISCONSIN
From 20-JUL-10 18:29:00 to 20-JUL-10 18:29:00 (CST-6)
Location: DARBOY
Magnitude: 1.25 
Property damage: 300.00K
Reported by: Insurance Company

Half dollar size hail and strong winds caused damage to 150 homes near Darboy.  The homes sustained at least minor damage to roofs and siding.

Hail in MARATHON, WISCONSIN
From 20-JUL-10 15:16:00 to 20-JUL-10 15:16:00 (CST-6)
Location: LITTLE CHICAGO
Magnitude: 1.00 
Reported by: Public

Quarter size hail fell at a restaurant near Little Chicago.

Hail in MARATHON, WISCONSIN
From 20-JUL-10 15:30:00 to 20-JUL-10 15:30:00 (CST-6)
Location: (AUW)WAUSAW MUNI ARP
Magnitude: 0.88 
Reported by: Public

Nickel size hail fell at Wausau.

Hail in MARATHON, WISCONSIN
From 20-JUL-10 15:42:00 to 20-JUL-10 15:42:00 (CST-6)
Location: WAUSAU
Magnitude: 1.00 
Reported by: Trained Spotter

Quarter size hail fell in downtown Wausau.

Hail in SHAWANO, WISCONSIN
From 20-JUL-10 16:30:00 to 20-JUL-10 16:30:00 (CST-6)
Location: TILLEDA
Magnitude: 1.75 
Reported by: Law Enforcement

Golf ball size hail fell at State Highway 29 and Old 29 Road.

Thunderstorm Wind in WAUPACA, WISCONSIN
From 20-JUL-10 17:50:00 to 20-JUL-10 17:50:00 (CST-6)
Location: NEW LONDON
Magnitude: 70.00 EG
Reported by: Trained Spotter

Thunderstorm wind gusts to 80 mph downed numerous trees and power lines, making State Highway 54 from Northport to New London nearly impassible.

Thunderstorm Wind in WAUPACA, WISCONSIN
From 20-JUL-10 17:52:00 to 20-JUL-10 17:52:00 (CST-6)
Location: NEW LONDON
Magnitude: 56.00 MG
Reported by: Trained Spotter

A spotter measured a thunderstorm wind gust of 65 mph at New London.

Hail in WAUPACA, WISCONSIN
From 20-JUL-10 16:56:00 to 20-JUL-10 16:56:00 (CST-6)
Location: CLINTONVILLE
Magnitude: 1.50 
Reported by: Trained Spotter

Ping pong ball size hail fell at the intersection of Duwe Road and Kratzke Road near Clintonville.

Hail in OUTAGAMIE, WISCONSIN
From 20-JUL-10 15:40:00 to 20-JUL-10 15:40:00 (CST-6)
Location: GREENVILLE
Magnitude: 1.75 
Reported by: Trained Spotter

Golf ball size hail fell near Greenville.

Hail in OUTAGAMIE, WISCONSIN
From 20-JUL-10 18:05:00 to 20-JUL-10 18:05:00 (CST-6)
Location: GREENVILLE
Magnitude: 1.75 
Reported by: Trained Spotter

Golf ball size hail fell near Greenville.

Hail in OUTAGAMIE, WISCONSIN
From 20-JUL-10 18:15:00 to 20-JUL-10 18:15:00 (CST-6)
Location: DARBOY
Magnitude: 1.00 
Reported by: NWS Employee

Quarter size hail fell near Appleton at the intersection of U.S. Highway 441 and Calumet Street.

Hail in WINNEBAGO, WISCONSIN
From 20-JUL-10 18:20:00 to 20-JUL-10 18:20:00 (CST-6)
Location: MENASHA
Magnitude: 1.75 
Reported by: Trained Spotter

Golf ball size hail near Menasha caused extensive damage to the roof and siding of a house.

Hail in WINNEBAGO, WISCONSIN
From 20-JUL-10 18:24:00 to 20-JUL-10 18:24:00 (CST-6)
Location: MENASHA
Magnitude: 1.25 
Reported by: Trained Spotter

Quarter to half dollar size hail fell near Menasha.

Hail in CALUMET, WISCONSIN
From 20-JUL-10 18:45:00 to 20-JUL-10 18:45:00 (CST-6)
Location: STOCKBRIDGE
Magnitude: 1.00 
Reported by: Trained Spotter

Quarter size hail fell near Stockbridge.

Thunderstorm Wind in CALUMET, WISCONSIN
From 20-JUL-10 19:10:00 to 20-JUL-10 19:10:00 (CST-6)
Location: CHILTON
Magnitude: 61.00 EG
Reported by: Trained Spotter

Thunderstorm wind gusts to 70 mph tossed a carport 100 feet, dropping it onto a road in Chilton.

Thunderstorm Wind in CALUMET, WISCONSIN
From 20-JUL-10 19:30:00 to 20-JUL-10 19:30:00 (CST-6)
Location: DARBOY
Magnitude: 52.00 EG
Reported by: Emergency Manager

Thunderstorm winds to 60 mph downed trees and power lines south of U.S. Highway 10 near Darboy.

Thunderstorm Wind in CALUMET, WISCONSIN
From 20-JUL-10 18:32:00 to 20-JUL-10 18:32:00 (CST-6)
Location: HIGH CLIFF
Magnitude: 54.00 MG
Reported by: Public

A thunderstorm gust of 62 mph was measured at Sherwood.

Hail in CALUMET, WISCONSIN
From 20-JUL-10 18:32:00 to 20-JUL-10 18:32:00 (CST-6)
Location: HIGH CLIFF
Magnitude: 1.75 
Reported by: Public

Golf ball size hail fell at Sherwood.

Thunderstorm Wind in OUTAGAMIE, WISCONSIN
From 20-JUL-10 18:01:00 to 20-JUL-10 18:01:00 (CST-6)
Location: HORTONVILLE
Magnitude: 70.00 EG
Reported by: NWS Storm Survey

Thunderstorm downburst winds uprooted or snapped about 65 trees on the northeast side of Hortonville and damaged a shed and playground equipment.

Thunderstorm Wind in OUTAGAMIE, WISCONSIN
From 20-JUL-10 18:15:00 to 20-JUL-10 18:15:00 (CST-6)
Location: APPLETON
Magnitude: 56.00 EG
Reported by: Emergency Manager

Thunderstorm winds downed numerous trees and damaged 3 to 4 homes in the Grand Chute area.

Hail in OUTAGAMIE, WISCONSIN
From 20-JUL-10 18:15:00 to 20-JUL-10 18:15:00 (CST-6)
Location: APPLETON
Magnitude: 1.00 
Reported by: NWS Employee

Quarter size hail fell in the Applegate subdivision.

Thunderstorm Wind in SHAWANO, WISCONSIN
From 20-JUL-10 16:10:00 to 20-JUL-10 16:10:00 (CST-6)
Location: BIRNAMWOOD
Magnitude: 78.00 EG
Reported by: Trained Spotter

Thunderstorm winds downed trees in Birnamwood and tore the roof from a telephone building.

Thunderstorm Wind in MARATHON, WISCONSIN
From 20-JUL-10 16:10:00 to 20-JUL-10 16:10:00 (CST-6)
Location: ROZELLVILLE
Magnitude: 52.00 EG
Reported by: Amateur Radio

Thunderstorm winds estimated at 60 mph were reported by an amateur radio operator at the intersection of County Highways C and M.

Thunderstorm Wind in PORTAGE, WISCONSIN
From 20-JUL-10 17:17:00 to 20-JUL-10 17:17:00 (CST-6)
Location: NELSONVILLE
Magnitude: 52.00 EG
Reported by: Trained Spotter

Thunderstorm winds downed several one-foot diameter trees north of Amherst.

Hail in PORTAGE, WISCONSIN
From 20-JUL-10 17:07:00 to 20-JUL-10 17:17:00 (CST-6)
Location: NELSONVILLE
Magnitude: 0.75 
Reported by: Trained Spotter

Penny size hail fell for ten minutes north of Amherst.

Thunderstorm Wind in OUTAGAMIE, WISCONSIN
From 20-JUL-10 18:05:00 to 20-JUL-10 18:05:00 (CST-6)
Location: GREENVILLE
Magnitude: 52.00 MG
Reported by: Trained Spotter

A thunderstorm wind gust of 60 mph was measured at Greenville.

Thunderstorm Wind in OUTAGAMIE, WISCONSIN
From 20-JUL-10 18:15:00 to 20-JUL-10 18:15:00 (CST-6)
Location: APPLETON
Magnitude: 56.00 EG
Reported by: NWS Employee

Thunderstorm winds caused widespread tree damage in the Applegate subdivision.

Lightning in MARATHON, WISCONSIN
From 20-JUL-10 16:45:00 to 20-JUL-10 16:45:00 (CST-6)
Location: ROZELLVILLE
Property damage: 4.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Lightning struck a house near Stratford causing roof and electrical damage.

Thunderstorm Wind in MARATHON, WISCONSIN
From 20-JUL-10 16:30:00 to 20-JUL-10 16:30:00 (CST-6)
Location: INGERSOLL
Magnitude: 52.00 EG
Reported by: Trained Spotter

Thunderstorm winds downed large trees on County Highway II near State Highway 49.

Thunderstorm Wind in MARATHON, WISCONSIN
From 20-JUL-10 16:10:00 to 20-JUL-10 16:10:00 (CST-6)
Location: INGERSOLL
Magnitude: 74.00 EG
Property damage: 211.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Downburst winds from a thunderstorm caused a barn to collapse, killing or severely injuring 50 head of milking cattle.  Part of the milking parlor also collapsed.  A flat-bed trailer with irrigation piping was moved about 20 feet, with some of the piping blown over an adjacent residence and into a stand of pine trees.  Less than a mile to the east the metal roof of a 25 foot by 25 foot shed was blown about 30 yards into an adjacent corn field.