EF1 tornado in Johnson County, Illinois

The tornado crossed into Johnson County from Massac County in the vicinity of Interstate 24. A barn was destroyed just before where the tornado crossed Interstate 24. Significant tree damage was observed near the community of Ganntown, where trees were snapped and uprooted and a home had minor damage. The metal roof of the house was damaged. On the west side of Grantsburg, a 20-by-50 foot pole barn was destroyed, and swirls were seen in tall grass. Near the end of the damage path in the Shawnee National Forest, over 100 trees were snapped or uprooted. Peak winds were estimated near 100 mph. The average path width was 150 yards.

Numerous strong to severe thunderstorms occurred in the warm sector of a low pressure system over central Missouri. The air mass in the warm sector was very unstable, with afternoon mixed-layer cape values in the 2500 to 4000 j/kg range. A 65 to 75 knot mid level jet was located across Arkansas, with the nose of the jet moving into western Kentucky. This feature enhanced the lift and strong deep-layer shear already in place, creating an environment very favorable for supercells and tornadoes. A 40 to 55 knot low level jet across eastern Arkansas moved into western Kentucky during the evening, resulting in isolated tornadoes and widespread damaging winds.