EF4 tornado in Williamson County, Illinois

A violent EF-4 tornado with peak winds of 190 mph impacted southern Williamson County, IL, during the early evening hours of Friday, May 16, 2025. The tornado began near the intersection of Spillway Road and Grassy Road doing mainly tree damage. As it moved eastward, the tornado intensified as it approached I-57. The tornado strengthened to EF-3 levels, where it removed the roofs of several homes of the staff of the U.S. Penitentiary just south of the main prison complex. The tornado debarked, and reduced to stubs, numerous trees adjacent to I-57. Multiple videos of this tornado were taken around the time it crossed I-57. The tornado continued at EF-3 strength as it damaged homes along IL-37 and north of Hudgens Road. The tornado reached peak intensity after crossing Market Road and into a subdivision just east of Andrew Road and north of Quarter Horse Road. Four homes on Kyler Court and Leslie Court sustained EF-3 damage. In addition, a newer two-story home with standard construction was completely swept off its foundation at the end of Kyler Court, which supported a rating of EF-4 with peak winds of 190 mph. The wooded area just east of Kyler Court saw extreme stubbing and some debarking of trees. The tornado continued eastward, destroying or severely damaging several homes at EF-2 or EF-3 strength on Wards Mill Road. Additional homes were destroyed at EF-3 damage levels a couple miles to the east on Highway 166. After crossing Highway 166, the tornado turned to the east-southeast and began to weaken, eventually lifting near the intersection of Mauseyville Road and Tyler Bridge Road. There were no fatalities, but seven people sustained non-life-threatening injuries.

A 500mb shortwave trough moved across the Upper Midwest with height falls across the Quad State during the afternoon and evening of the 16th. The exit region of a strong (125kt) upper level jet was positioned across the area as well. Low-level winds strengthened during the afternoon to 50kts at 850mb. Following the early AM convection, ample sunshine allowed for a very unstable airmass to develop with CAPE of 3000-4000J/kg with deep layer shear of 65-70kts. Late afternoon, STP peaked at 9 near the Wabash/Ohio River confluence with effective SRH of 300-400m2/s2. Mid-level lapse rates peaked at 8-8.5C/km for much of the Quad State with significant hail parameter of 3-5 mid-afternoon and DCAPE peaking at 1200-1500J/kg. Initial storm formation was discrete with very large hail and tornadoes, with storms becoming more linear later in the evening with the approach of a cold front.

Damage reports were widespread near and south of IL-13 in Southern Illinois. An especially powerful supercell produced a violent tornado south of Marion with peak winds estimated at 190mph, the strongest in the Quad State region since the December 10, 2021 Western Kentucky tornado. The worst of the damage was between Andrew Rd and Wards Mill Rd with the EF-4 damage point a home swept off its foundation on Kyler Ct. This supercell would continue on to produce two more tornadoes (in Southeastern Saline and Southern Gallatin Counties) before crossing into Northwestern Kentucky. Large hail was commonplace with the afternoon supercells, with the largest reports being multiple baseball size hail reports in Pulaski County.