EF1 tornado in Williamson County, Illinois

This tornado skipped along the path, bringing down large tree limbs from Crab Orchard Lake to Interstate 57 a few miles north of Marion. Most of the tornado track was EF-0, except for an uprooted tree or two west of Interstate 57 near Whiteash. Peak winds were estimated near 95 mph.

Isolated supercell thunderstorms moved into southern Illinois during the evening hours. The storms developed ahead of a cold front in a destabilizing air mass characterized by dew points in the lower to mid 60's. The most intense supercell storm awaited the approach of a mid-level impulse from Oklahoma, which was downstream from the primary shortwave trough over the southern Plains. The supercell produced two long-track strong tornadoes, the first of which originated in Perry County, Missouri and tracked almost 50 miles before dissipating. The second strong tornado formed in the Wabash Valley and crossed into southwest Indiana. A southwesterly low-level jet increased substantially during the evening, creating favorable conditions for tornadoes.