A line of severe thunderstorms developed ahead of a cold front during the late afternoon and evening of May 20th.  These thunderstorms produced hail with several microbursts also occurring, producing damaging winds.

Hail in MCHENRY, ILLINOIS
From 20-MAY-12 15:10:00 to 20-MAY-12 15:11:00 (CST-6)
Location: MARENGO
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in MCHENRY, ILLINOIS
From 20-MAY-12 15:15:00 to 20-MAY-12 15:16:00 (CST-6)
Location: HARTLAND
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Quarter size hail was reported on Alden Road.

Hail in MCHENRY, ILLINOIS
From 20-MAY-12 15:23:00 to 20-MAY-12 15:24:00 (CST-6)
Location: WOODSTOCK ARPT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Quarter size hail was reported at US 14 and Kishwaukee Valley Road.

Hail in DU PAGE, ILLINOIS
From 20-MAY-12 20:00:00 to 20-MAY-12 20:02:00 (CST-6)
Location: WILLOWBROOK
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in LEE, ILLINOIS
From 20-MAY-12 14:55:00 to 20-MAY-12 14:57:00 (CST-6)
Location: PAW PAW
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Thunderstorm Wind in MCHENRY, ILLINOIS
From 20-MAY-12 15:00:00 to 20-MAY-12 15:00:00 (CST-6)
Location: MARENGO
Magnitude: 65.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in LEE, ILLINOIS
From 20-MAY-12 15:01:00 to 20-MAY-12 15:01:00 (CST-6)
Location: PAW PAW
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in MCHENRY, ILLINOIS
From 20-MAY-12 15:10:00 to 20-MAY-12 15:10:00 (CST-6)
Location: MARENGO
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in KANE, ILLINOIS
From 20-MAY-12 16:35:00 to 20-MAY-12 16:39:00 (CST-6)
Location: KANEVILLE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Penny size hail fell near Harter Road and Lasher Road.

Hail in KANE, ILLINOIS
From 20-MAY-12 16:48:00 to 20-MAY-12 16:50:00 (CST-6)
Location: ELBURN
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in GRUNDY, ILLINOIS
From 20-MAY-12 17:04:00 to 20-MAY-12 17:06:00 (CST-6)
Location: MORRIS
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in LIVINGSTON, ILLINOIS
From 20-MAY-12 17:42:00 to 20-MAY-12 17:44:00 (CST-6)
Location: DWIGHT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in KANKAKEE, ILLINOIS
From 20-MAY-12 18:06:00 to 20-MAY-12 18:06:00 (CST-6)
Location: SHERBURNVILLE
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A wind gust to 59 mph was measured near State Line Road and 10500 North.

Hail in GRUNDY, ILLINOIS
From 20-MAY-12 17:08:00 to 20-MAY-12 17:10:00 (CST-6)
Location: MORRIS
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several reports of hail up to the size of quarters came in from Morris, including at the intersections of Union and Route 6, Route 6 and Route 47, as well as McKinley Street and Route 47.