An organized severe weather outbreak affected southern Illinois with numerous damaging wind gusts and isolated large hail. Most of the damaging winds were south of the Marion-Carbondale area. The storms formed along and south of a stalled front that was over southern Illinois and southern Indiana. By the afternoon hours, large amounts of moisture and instability were present, along with plenty of deep-layer wind shear. As a mid-level disturbance lifted out of the Southern Plains, multiple storm clusters and bowing segments formed across Missouri and southern Illinois in a very favorable environment for severe thunderstorms. Dew points were in the lower 70's in many locations in the afternoon, coupled with surface cape values of 3000-4000 j/kg. Boundaries left over from early morning storms also played a role in the placement of afternoon thunderstorm development. Multiple rounds of severe thunderstorms impacted the Middle Mississippi Valley on the first day of the Memorial Day holiday weekend. There were two or three bowing lines of thunderstorms that impacted the region with damaging winds. Individual cells and clusters also developed early on in the event, producing mainly large hail. Multiple rounds of storms over the same locations also resulted in a few flooding issues.

Thunderstorm Wind in MASSAC, ILLINOIS
From 27-MAY-17 15:11:00 to 27-MAY-17 15:26:00 (CST-6)
Location: BOAZ
Magnitude: 70.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A swath of damaging winds crossed northern and central Massac County. Wind speeds estimated up to 80 mph broke utility poles, snapped numerous trees, and blew down a barn. On the western side of the county, power poles were snapped near the intersection of Highway 169 and County Road 12. On the eastern side of the county, a barn was blown down east of Highway 145 near County Road 2. Some of the most concentrated damage was in the New Columbia area, where numerous trees were snapped and uprooted. Shingles were blown off a house on the northwest side of New Columbia. Large tree limbs were blown down on U.S. Highway 45 north of Mermet.

Thunderstorm Wind in JOHNSON, ILLINOIS
From 27-MAY-17 15:15:00 to 27-MAY-17 15:15:00 (CST-6)
Location: TUNNEL HILL
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A few trees were down.

Thunderstorm Wind in POPE, ILLINOIS
From 27-MAY-17 15:28:00 to 27-MAY-17 15:28:00 (CST-6)
Location: TEMPLE HILL
Magnitude: 61.00 EG
Property damage: 6.00K
Crop damage: 0.00K
Reported by: Social Media

Some trees were snapped or uprooted.

Thunderstorm Wind in UNION, ILLINOIS
From 27-MAY-17 16:50:00 to 27-MAY-17 17:00:00 (CST-6)
Location: JONESBORO
Magnitude: 70.00 EG
Property damage: 60.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Widespread wind damage was reported across Jonesboro, including a collapsed garage due to a tree falling on it. Numerous power poles were snapped across town. Numerous trees and power lines were down across the west side of Jonesboro. Some of the trees were up to five feet in diameter. In Anna, a large tree and numerous limbs were down.

Hail in WHITE, ILLINOIS
From 27-MAY-17 14:28:00 to 27-MAY-17 14:28:00 (CST-6)
Location: CROSSVILLE
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in PULASKI, ILLINOIS
From 27-MAY-17 16:59:00 to 27-MAY-17 16:59:00 (CST-6)
Location: ULLIN
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A trained spotter estimated the wind gusted to 70 mph.

Hail in HAMILTON, ILLINOIS
From 27-MAY-17 13:42:00 to 27-MAY-17 13:53:00 (CST-6)
Location: MC LEANSBORO
Magnitude: 1.75 
Reported by: Trained Spotter

A swath of large hail from quarter to golf-ball size crossed the Mcleansboro area in association with a severe thunderstorm cell.

Thunderstorm Wind in JACKSON, ILLINOIS
From 27-MAY-17 14:25:00 to 27-MAY-17 14:40:00 (CST-6)
Location: MURPHYSBORO
Magnitude: 56.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Some tree damage occurred in the Murphysboro to Carbondale corridor. A tree was blown down on the west side of the city of Murphysboro. In Carbondale, there were at least a couple of snapped or uprooted trees.

Thunderstorm Wind in JEFFERSON, ILLINOIS
From 27-MAY-17 14:46:00 to 27-MAY-17 14:46:00 (CST-6)
Location: MT VERNON
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Numerous trees and limbs were blown down on the southwest edge of Mt. Vernon. A large limb landed on a home. Most of the tree damage was along and just north of Route 148.

Thunderstorm Wind in WILLIAMSON, ILLINOIS
From 27-MAY-17 15:05:00 to 27-MAY-17 15:05:00 (CST-6)
Location: CREAL SPGS
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous trees were blown down across the far southern part of the county near Creal Springs.

Thunderstorm Wind in JOHNSON, ILLINOIS
From 27-MAY-17 15:04:00 to 27-MAY-17 15:19:00 (CST-6)
Location: CYPRESS
Magnitude: 61.00 EG
Property damage: 40.00K
Crop damage: 0.00K
Reported by: Public

Numerous trees were blown down in the county, especially the southern half of the county. Several trees were blown down on U.S. Route 45, blocking the road completely. Large tree limbs were down in the yard of a residence in Vienna, and four medium to large trees were down at a neighboring residence. Ten to fifteen shingles were blown off a house at Vienna. A few miles west of Vienna, trees were blown over a roadway. Other tree damage occurred between Vienna and Cypress. Within one-half mile of the Massac County line on U.S. Highway 45, large tree limbs were broken, and about a dozen shingles were blown off of a roof.