Major flash flooding struck parts of far southern Illinois. The hardest hit counties were Alexander, Pulaski, and Massac in the southern tip of Illinois. Widespread flash flooding of roads made travel difficult or impossible for several hours during the peak of the heaviest rainfall in the morning. There was a bridge that was washed out in Massac County on a secondary road. Among the most impactful road closures was Interstate 57 in Pulaski County. Illinois Route 3 was closed to most vehicles except large trucks at the underpass on the north side of Cairo. Several water rescues were conducted for people stranded in vehicles in Massac, Pulaski, and Alexander Counties. A number of roads were washed out in several counties. The impacts in the Marion, Carbondale, and Herrin areas consisted of street flooding, as well as some minor flooding of a few structures in flood-prone areas. Widespread rainfall totals ranging from 5 to 9 inches occurred along and south of a line from Carbondale to Marion, including the Cairo and Metropolis areas. The majority of this rain fell within a 10-hour window between midnight and 10 AM. The highest reported rainfall total was 8.68 inches in Ullin (Pulaski County). The co-op site near Cairo received 7.83 of rain.
The historic rainfall event was caused by a persistent thunderstorm complex that continually regenerated as it moved southeast across the region during the early morning hours of the 19th. This complex of thunderstorms was indirectly caused by the complex of severe thunderstorms during the midday hours of the 18th. The complex on the 18th left an outflow boundary from south central Missouri into northeast Arkansas. This boundary lifted back northeast into southeast Missouri during the overnight and early morning hours of July 19th. At the same time, a southwest low-level jet ramped up over the top of the surface boundary. Extremely high moisture levels were present, with precipitable water values up to 2.3 inches. The position of the boundary oriented parallel with the upper-level wind flow provided an ideal setup for training convection over the same areas. The initial storms blew up by 11 PM and continued to channel southeastward across the same areas through the following morning.

Hail in JOHNSON, ILLINOIS
From 19-JUL-23 03:39:00 to 19-JUL-23 03:39:00 (CST-6)
Location: TUNNEL HILL
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in UNION, ILLINOIS
From 19-JUL-23 06:01:00 to 19-JUL-23 06:01:00 (CST-6)
Location: MILL CREEK
Magnitude: 52.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A tree was blown over a road.

Flash Flood in PULASKI, ILLINOIS
From 19-JUL-23 04:00:00 to 19-JUL-23 15:00:00 (CST-6)
Location: MOUND CITY
Flood cause: Heavy Rain
Property damage: 150.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Flash Flood in WILLIAMSON, ILLINOIS
From 19-JUL-23 05:08:00 to 19-JUL-23 09:30:00 (CST-6)
Location: CARTERVILLE
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Public

Flash Flood in JACKSON, ILLINOIS
From 19-JUL-23 06:23:00 to 19-JUL-23 12:00:00 (CST-6)
Location: REEDS
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Public

Flash Flood in MASSAC, ILLINOIS
From 19-JUL-23 06:30:00 to 19-JUL-23 15:00:00 (CST-6)
Location: ROUND KNOB
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Public

Flash Flood in ALEXANDER, ILLINOIS
From 19-JUL-23 06:45:00 to 19-JUL-23 11:00:00 (CST-6)
Location: CAIRO
Flood cause: Heavy Rain
Property damage: 150.00K
Crop damage: 0.00K
Reported by: Broadcast Media