EF2 tornado in Williamson County, Illinois

The tornado was spawned by the same supercell that produced an EF-2 tornado in Union and extreme southeast Jackson Counties. The tornado touched down in the Crab Orchard National Wildlife Refuge, just southeast of Little Grassy Lake. The tornado moved east-northeast across Interstate 57, passing south of Marion. A large metal warehouse building was heavily damaged. Numerous homes sustained mainly minor roof damage. Hundreds of trees were snapped or uprooted, and many power lines were blown down. Several barns and outbuildings were destroyed or heavily damaged. The peak EF-2 intensity estimate was based on damage southeast of Marion, near the location where the tornado crossed Highway 166. Peak winds were estimated near 120 mph. The average path width was 250 yards.

A squall line with embedded sustained supercells crossed southern Illinois. The embedded supercells raced east-northeast at 60 to 70 mph, while the line moved southeast at a slower rate. The storms strengthened as they encountered richer low-level moisture, with surface dew points around 60 degrees spreading rapidly north-northeastward up the Mississippi Valley. Intense low to mid-level wind fields maintained the intensity of tornadic storms despite weak instability due to lack of solar heating. A south-southwesterly low level jet from 60 to 70 knots veered to west-southwest around 75 knots at 500 mb.