EF3 tornado in Jackson County, Illinois

This large tornado entered Jackson County from Randolph County near the community of Rockwood. The tornado originally began near Perryville, Missouri, where it achieved its peak intensity in the EF-4 category. The tornado crossed the entire width of Jackson County, entering the county about two miles from the Mississippi River. The tornado passed just south of Ava, clipped the southern edge of Vergennes, and then passed near the north edge of Elkville before exiting the northeast corner of the county. In Jackson County, the tornado reached a maximum intensity of EF-3 on the south end of Vergennes. Winds estimated near 145 mph destroyed a house. The wood house was not securely anchored to the foundation, and other construction details suggested wind speeds were below the EF-4 category. Elsewhere in Jackson County, the tornado passed through mainly rural farmlands and woods. Thousands of large trees were snapped and uprooted, and dozens of homes and other structures were damaged or destroyed. The tornado remained quite wide, nearly one-third of a mile at times. The average path width in Jackson County was about 600 yards. The tornado continued east-northeast into Franklin County.

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.