EF4 tornado in Saline County, Illinois

The tornado touched down about a mile north of Carrier Mills, then moved east-northeast through Harrisburg. The violent tornado produced a swath of devastation in south and southeast parts of Harrisburg. In Harrisburg, over 200 homes and about 25 businesses were heavily damaged or destroyed. The damage was in residential neighborhoods in the far south and southeast sections of Harrisburg. The commercial strip along U.S. Highway 45 in the south part of the city was directly impacted. A strip mall on the east side of U.S. Route 45 was destroyed. The tornado struck the Harrisburg medical center and surrounding residences on the southeast side of town. At least ten homes or other buildings were levelled, with several home structures displaced from their foundations. The neighborhood with the levelled homes and fatalities was adjacent to the destroyed strip mall. The tornado proceeded across Illinois Route 13 a few miles east of Harrisburg, destroying a farm house and a business. Hundreds of large trees were snapped or uprooted, along with many downed power lines. Peak winds were estimated near 180 mph based on numerous levelled and displaced homes. The average path width was 275 yards. The tornado continued into Gallatin County shortly after crossing Highway 142.

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.