EF2 tornado in Union County, Illinois

The tornado crossed the Mississippi River from Cape Girardeau County into northwestern Union County. After exiting cropland in the Mississippi River floodplain, the tornado tracked through the Shawnee National Forest. The damage path extended just north of Bald Knob, then directly across Alto Pass. Thousands of trees were snapped or uprooted, and several houses were damaged. The houses that were damaged suffered primarily partial roof loss. The houses were located in Alto Pass, where EF-2 damage occurred. Numerous barns and grain bins were destroyed. Many power lines were blown down. Peak winds were estimated near 115 mph. The average path width was 250 yards. The tornado path crossed into Giant City State Park and into the southeast corner of Jackson County.

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.