A cold front moving through the region was the focus for development of a broken line of thunderstorms ahead of the front during the afternoon and evening.  The combination of ascent with a short wave impulse passing over the region, daytime heating, low-level moisture inflow on a 40 knot west southwest low-level jet, and steep low to mid-level lapse rates produced severe thunderstorms with large hail and damaging wind gusts.  Additionally, the storms produced a brief, EF0 tornado in Rock County, southeast of Janesville.

Tornado in ROCK, WISCONSIN
From 21-SEP-10 15:00:00 to 21-SEP-10 15:01:00 (CST-6)
Location: PRAIRIE AIRPORT
Tornado F-scale: EF0
Property damage: 1.00K
Reported by: Amateur Radio

An isolated thunderstorm cell ahead of a broken line of strong to severe thunderstorms, generated a brief, weak tornado.  A damage survey conducted by Midwest Severe Storm Tracking and Response Center verified this brief, EF0 tornado around 4.2 miles southeast of Southern Wisconsin Regional Airport (KJVL).  The tornado path began just southeast of the intersection of CTH G and Walton Lane, and moved east-northeast less than 1/2 mile before dissipating east of Franklin Street.  The tornado broke off 6 to 8 inch tree limbs and twisted and broke off shrubs at the ground.  It also bent, and then knocked over, a 20-foot antenna that had been stabilized by guy wires.  The EF rating was determined by DI27 (TH) DOD2, with estimated wind speeds of 70 to 75 mph.  The exact start location is Lat. 42.56200 Lon. -89.01098.  The exact end location is Lat 42.56322 Lon -89.00297.
Average path width was 15 yards.  The damage amount was estimated.

Hail in GREEN, WISCONSIN
From 21-SEP-10 15:00:00 to 21-SEP-10 15:08:00 (CST-6)
Location: BRODHEAD
Magnitude: 1.00 
Reported by: Public

Hail in WALWORTH, WISCONSIN
From 21-SEP-10 15:50:00 to 21-SEP-10 15:50:00 (CST-6)
Location: ALLEN GROVE
Magnitude: 1.00 
Reported by: Law Enforcement

Hail in MILWAUKEE, WISCONSIN
From 21-SEP-10 16:33:00 to 21-SEP-10 16:33:00 (CST-6)
Location: FRANKLIN
Magnitude: 1.00 
Reported by: Amateur Radio

Hail in KENOSHA, WISCONSIN
From 21-SEP-10 16:40:00 to 21-SEP-10 16:40:00 (CST-6)
Location: BRISTOL
Magnitude: 1.75 
Reported by: Law Enforcement

Thunderstorm Wind in RACINE, WISCONSIN
From 21-SEP-10 16:40:00 to 21-SEP-10 16:40:00 (CST-6)
Location: WIND LAKE
Magnitude: 52.00 EG
Reported by: Law Enforcement

Law enforcement reported a thunderstorm wind gust estimated at 52 knots (60 mph).

Thunderstorm Wind in RACINE, WISCONSIN
From 21-SEP-10 16:45:00 to 21-SEP-10 16:45:00 (CST-6)
Location: CALEDONIA
Magnitude: 52.00 EG
Reported by: Law Enforcement

An amateur radio operator reported a thunderstorm wind gust estimated at 52 knots (60 mph).

Hail in WALWORTH, WISCONSIN
From 21-SEP-10 16:09:00 to 21-SEP-10 16:09:00 (CST-6)
Location: EAST TROY
Magnitude: 1.00 
Reported by: Trained Spotter

Hail in RACINE, WISCONSIN
From 21-SEP-10 16:47:00 to 21-SEP-10 16:47:00 (CST-6)
Location: CALEDONIA
Magnitude: 1.00 
Reported by: Law Enforcement

Thunderstorm Wind in ROCK, WISCONSIN
From 21-SEP-10 15:25:00 to 21-SEP-10 15:25:00 (CST-6)
Location: BELOIT
Magnitude: 52.00 EG
Reported by: Law Enforcement

Law enforcement officials reported several trees were blown down by thunderstorm wind gusts estimated at 52 knots (60 mph).

Thunderstorm Wind in KENOSHA, WISCONSIN
From 21-SEP-10 17:02:00 to 21-SEP-10 17:02:00 (CST-6)
Location: SILVER LAKE
Magnitude: 52.00 EG
Reported by: Law Enforcement

Law enforcement officials reported several trees were blown down by thunderstorm wind gusts estimated at 52 knots (60 mph).

Hail in ROCK, WISCONSIN
From 21-SEP-10 15:30:00 to 21-SEP-10 15:30:00 (CST-6)
Location: (JVL)ROCK CO ARPT JA
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in ROCK, WISCONSIN
From 21-SEP-10 15:34:00 to 21-SEP-10 15:34:00 (CST-6)
Location: BELOIT
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in WALWORTH, WISCONSIN
From 21-SEP-10 15:57:00 to 21-SEP-10 15:57:00 (CST-6)
Location: DARIEN
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Hail in WALWORTH, WISCONSIN
From 21-SEP-10 15:58:00 to 21-SEP-10 15:58:00 (CST-6)
Location: DELAVAN LAKE
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in RACINE, WISCONSIN
From 21-SEP-10 16:32:00 to 21-SEP-10 16:32:00 (CST-6)
Location: ROCHESTER
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement