Isolated supercell thunderstorms developed during the late afternoon over Livingston and McLean counties and tracked northeast toward the Chicago metro through the early evening.  There were two separate and brief EF-0 tornado touchdowns in Livingston County:  one near Cornell and the other north of Chenoa. No damage was observed with these brief touchdowns.  The supercell thunderstorm that produced a brief EF-0 tornado near Cornell maintained persistent rotation as it tracked across Grundy County, with numerous photos of a very low wall cloud, and reports of possible brief funnel clouds at times near Kinsman and Mazon.
A line of strong to severe storms producing torrential rainfall moved in behind the supercell thunderstorms, producing sporadic wind damage in portions of northern Illinois and also flash flooding in portions of Rockford.  Two additional EF-0 tornadoes associated with rotation embedded within the line of storms were confirmed:  the first from extreme southeast Naperville to far eastern Woodridge, and the second a brief path through Downers Grove.
The 2.87 of rain that fell at Rockford Airport on August 18th set a new record for the date, breaking the previous record set in 2005.

Thunderstorm Wind in WILL, ILLINOIS
From 18-AUG-15 19:05:00 to 18-AUG-15 19:05:00 (CST-6)
Location: BARBERS CORNERS
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Several 2-4 inch branches down and an 18-20 inch tree top snapped off in Green Valley Forest Preserve.

Tornado in DU PAGE, ILLINOIS
From 18-AUG-15 19:06:00 to 18-AUG-15 19:07:00 (CST-6)
Location: DOWNERS GROVE
Tornado F-scale: EF0
Property damage: 50.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A brief EF-0 tornado touched down in DuPage county in Downers Grove. Maximum winds were estimated at 70 mph, with a path length of 0.25 miles and path width of 50-75 yards.  A few hardwood trees snapped, one snapped a power pole and caused minor garage damage.  Also a car parked underneath pole was crushed.

Tornado in LIVINGSTON, ILLINOIS
From 18-AUG-15 15:32:00 to 18-AUG-15 15:33:00 (CST-6)
Location: CORNELL
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A brief touchdown was reported by law enforcement.  No damage occurred.

Tornado in DU PAGE, ILLINOIS
From 18-AUG-15 18:57:00 to 18-AUG-15 19:00:00 (CST-6)
Location: WOODRIDGE
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

This is a continuation of a tornado that began in Will County. A tornado touched down in extreme southeast Naperville, and several hardwood trees were snapped or damaged and a softwood tree uprooted. Maximum winds were estimated at 80 mph.

Tornado in LIVINGSTON, ILLINOIS
From 18-AUG-15 16:05:00 to 18-AUG-15 16:06:00 (CST-6)
Location: OCOYA
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter observed tornado just west of I-55. No damage occurred.

Thunderstorm Wind in GRUNDY, ILLINOIS
From 18-AUG-15 18:30:00 to 18-AUG-15 18:32:00 (CST-6)
Location: CENTRAL CITY
Magnitude: 65.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Social Media

Roof off of garage in Central City neighborhood just north of Braceville. Small tree limbs and power lines down in the area.  Also, Gardner Fire Department estimated 60 mph winds.

Tornado in WILL, ILLINOIS
From 18-AUG-15 18:55:00 to 18-AUG-15 18:57:00 (CST-6)
Location: (1C5) BOLINGBROOK CLOW AIRPORT
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A tornado touched down in extreme southeast Naperville, and several hardwood trees were snapped or damaged and a softwood tree uprooted. Maximum winds were estimated at 80 mph. This tornado continued into DuPage county.

Flash Flood in WINNEBAGO, ILLINOIS
From 18-AUG-15 18:03:00 to 19-AUG-15 01:00:00 (CST-6)
Location: CAMP GRANT
Flood cause: Heavy Rain
Property damage: 300.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Numerous reports of high water and drainage issues across the northeast and southeast portions of Rockford.  Cars were stranded in standing water. Areas hit were the intersections of Sandy Hollow and Alpine, as well as streets north of 9th Avenue between 11th and 15th Streets, Churchill Park and the intersection of State and Perryville.  Numerous reports of flooded basements.