The first round of severe thunderstorms to affect southern Illinois occurred during the late morning hours. Most of the severe weather was in the form of large hail during this episode. The first storm became severe just south of Mount Vernon and tracked east along the Hamilton/Wayne County border. Other severe storms developed across the Marion and Herrin areas, producing copious amounts of large hail in Herrin. There was wind damage in Carterville and the Cambria area of Williamson County, where trees and power lines were down. Roads were blocked by fallen trees in Carterville and just south of Cambria. Five to six houses were struck by falling trees, mainly on the west side of Carterville. Major damage occurred to some of the houses. At John A. Logan College near Carterville, numerous trees and limbs were down, destroying fencing and a light pole. These severe storms then moved east and consolidated into a supercell in southern Saline County, just south of Harrisburg. As the supercell crossed Hardin County, a 12-mile long swath of wind damage occurred. The wind damage was primarily in the Shawnee National Forest, resulting in little structural damage until the storm reached Cave-In-Rock, a small town on the Ohio River. At Cave-In-Rock, there were trees down, including at least ten on structures. At the Cave-In-Rock State Park campground near the Ohio River, tents were blown away, and about 20 trees and many more limbs were blown down. Torrential downpours caused street flooding in Cave-In-Rock, and water seeped into the post office and a cafe.

Hail in HARDIN, ILLINOIS
From 26-MAY-04 10:50:00 to 26-MAY-04 11:00:00 (CST)
Location: KARBERS RIDGE
Magnitude: 1.25 
Reported by: GENERAL PUBLIC

Hail in JACKSON, ILLINOIS
From 26-MAY-04 09:19:00 to 26-MAY-04 09:19:00 (CST)
Location: CARBONDALE
Magnitude: 1.00 
Reported by: TRAINED SPOTTER

Hail in JEFFERSON, ILLINOIS
From 26-MAY-04 08:50:00 to 26-MAY-04 08:56:00 (CST)
Location: MT VERNON
Magnitude: 0.88 
Reported by: TRAINED SPOTTER

Hail in HAMILTON, ILLINOIS
From 26-MAY-04 09:06:00 to 26-MAY-04 09:20:00 (CST)
Location: DAHLGREN
Magnitude: 1.75 
Reported by: TRAINED SPOTTER

Heavy Rain in HARDIN, ILLINOIS
From 26-MAY-04 10:52:00 to 26-MAY-04 11:30:00 (CST)
Location: CAVE IN ROCK
Reported by: NEWSPAPER

Thunderstorm Wind in WILLIAMSON, ILLINOIS
From 26-MAY-04 09:50:00 to 26-MAY-04 10:00:00 (CST)
Location: CAMBRIA
Magnitude: 60 EG
Property damage: 75K
Reported by: EMERGENCY MANAGER

Hail in WILLIAMSON, ILLINOIS
From 26-MAY-04 10:08:00 to 26-MAY-04 10:15:00 (CST)
Location: MARION
Magnitude: 1.00 
Reported by: TRAINED SPOTTER

Hail in WILLIAMSON, ILLINOIS
From 26-MAY-04 09:37:00 to 26-MAY-04 09:37:00 (CST)
Location: HERRIN
Magnitude: 1.75 
Reported by: TRAINED SPOTTER

Hail in WILLIAMSON, ILLINOIS
From 26-MAY-04 09:34:00 to 26-MAY-04 09:34:00 (CST)
Location: CRAB ORCHARD
Magnitude: 1.00 
Reported by: EMERGENCY MANAGER

Hail in SALINE, ILLINOIS
From 26-MAY-04 10:15:00 to 26-MAY-04 10:20:00 (CST)
Location: CARRIERS MILLS
Magnitude: 1.00 
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in HARDIN, ILLINOIS
From 26-MAY-04 10:45:00 to 26-MAY-04 11:00:00 (CST)
Location: KARBERS RIDGE
Magnitude: 65 EG
Property damage: 80K
Reported by: NWS STORM SURVEY