A slow moving cold front sagged south across northern Illinois during the evening of May 3rd.  Isolated severe thunderstorms initially developed over northern Illinois then became more widespread overnight as thunderstorms continued to develop upstream and train along the frontal boundary.

Hail in WILL, ILLINOIS
From 03-MAY-12 17:02:00 to 03-MAY-12 17:04:00 (CST-6)
Location: PLAINFIELD
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Hail in COOK, ILLINOIS
From 03-MAY-12 17:35:00 to 03-MAY-12 17:40:00 (CST-6)
Location: NILES
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Multiple reports of half dollar size hail were received between Niles and Morton Grove.

Hail in COOK, ILLINOIS
From 03-MAY-12 17:52:00 to 03-MAY-12 17:54:00 (CST-6)
Location: EVANSTON
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in COOK, ILLINOIS
From 03-MAY-12 18:12:00 to 03-MAY-12 18:18:00 (CST-6)
Location: DES PLAINES
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Multiple reports of quarter size hail were received between Des Plaines and Park Ridge, including a report near the intersection of Touhy Avenue and River Road.

Hail in COOK, ILLINOIS
From 03-MAY-12 18:18:00 to 03-MAY-12 18:23:00 (CST-6)
Location: NORRIDGE
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Multiple reports of hail up to the size of nickels were received between Norwood Park and Niles, including a report near the intersection of Touhy Avenue and Caldwell Avenue.

Hail in COOK, ILLINOIS
From 03-MAY-12 19:05:00 to 03-MAY-12 19:07:00 (CST-6)
Location: WEST GLENVIEW
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Dime to penny size hail was reported near the intersection of Golf Road and Shermer Road.

Hail in COOK, ILLINOIS
From 03-MAY-12 19:15:00 to 03-MAY-12 19:20:00 (CST-6)
Location: NILES
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in COOK, ILLINOIS
From 03-MAY-12 19:38:00 to 03-MAY-12 19:58:00 (CST-6)
Location: DUNNING
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous large hail reports were received from the near-north side of Chicago.  The largest report was of golfball size hail near the intersection of Milwaukee Avenue and Addison Street. Quarter to ping-pong ball size hail was reported near Harwood Heights, Portage Park, Old Irving Park, and just east of North Park.

Hail in COOK, ILLINOIS
From 03-MAY-12 20:02:00 to 03-MAY-12 20:05:00 (CST-6)
Location: AVONDALE
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Up to quarter size hail was reported from the intersection of Wilson Avenue and Broadway Street south to Wrigleyville.

Hail in COOK, ILLINOIS
From 03-MAY-12 20:54:00 to 03-MAY-12 20:59:00 (CST-6)
Location: OAK LAWN
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Multiple reports of hail to the size of quarters were received from Oak Lawn.

Hail in COOK, ILLINOIS
From 03-MAY-12 21:50:00 to 03-MAY-12 21:52:00 (CST-6)
Location: WORTH
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in LIVINGSTON, ILLINOIS
From 03-MAY-12 23:58:00 to 03-MAY-12 23:58:00 (CST-6)
Location: LONG PT
Magnitude: 60.00 EG
Crop damage: 0.00K
Reported by: Law Enforcement

Multiple utility poles and wires were blown down along with a few trees.

Thunderstorm Wind in LIVINGSTON, ILLINOIS
From 04-MAY-12 00:07:00 to 04-MAY-12 00:07:00 (CST-6)
Location: CORNELL
Magnitude: 60.00 EG
Crop damage: 0.00K
Reported by: Law Enforcement

Scattered wind damage was reported across Cornell, including a few trees and utility poles that were blown down.

Thunderstorm Wind in LIVINGSTON, ILLINOIS
From 04-MAY-12 00:15:00 to 04-MAY-12 00:15:00 (CST-6)
Location: ROWE
Magnitude: 56.00 MG
Crop damage: 0.00K
Reported by: Law Enforcement

A few trees and multiple utility poles were blown down in Pontiac.  A wind gust to 64 mph was measured at the airport.

Flash Flood in COOK, ILLINOIS
From 03-MAY-12 19:20:00 to 03-MAY-12 20:30:00 (CST-6)
Location: WEST GLENVIEW
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Dempster Street was flooded between Waukegan Road and Ozark Street.

Flash Flood in COOK, ILLINOIS
From 03-MAY-12 19:30:00 to 03-MAY-12 21:30:00 (CST-6)
Location: SKOKIE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

The intersection of Howard Street and Western Avenue was closed due to flooding.

Flash Flood in COOK, ILLINOIS
From 03-MAY-12 22:30:00 to 04-MAY-12 02:00:00 (CST-6)
Location: OAK LAWN
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Torrential rain fell across portions of southern Cook County causing roadways to be closed due to flooding.  Kedzie Avenue was flooded between 87th Street and 103rd Street.  Cicero Avenue was also closed near 103rd Street.  A report from a mile south-southwest of Oak Lawn indicated that 2.70 inches of rain fell in just an hour with a storm total of 3.20 inches.  Another report from 3 miles southwest of Midway Airport indicated that 0.85 inches of rain fell in 15 minutes.

Flash Flood in COOK, ILLINOIS
From 03-MAY-12 21:08:00 to 04-MAY-12 02:00:00 (CST-6)
Location: ENGLEWOOD
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Martin Luther King Drive between 51st Street and 55th Street and portions of Garfield Boulevard were impassable due to flash flooding.

Flash Flood in COOK, ILLINOIS
From 03-MAY-12 21:11:00 to 04-MAY-12 02:00:00 (CST-6)
Location: BROOKFIELD
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Ogden Avenue was impassable between Joliet Avenue and Lawndale Avenue.