Hail in Williamson County, Illinois

Giant hail occurred in a swath of Williamson County along Illinois Route 13. The swath of large hail began near the Marion/Williamson County airport, just east and southeast of Crainville. Hail slightly larger than baseballs pounded the area in the immediate vicinity of the Marion/Williamson County Regional Airport. Hail damage was reported to planes at the airport, including broken windows. Numerous vehicles were damaged by hail from quarter size to golf-ball size. Hail damage occurred at the baseball stadium near Interstate 57 at Route 13. There was major damage to multiple vehicles at a car dealership on Route 13 between the Marion airport and the downtown Marion area. The large hail swath continued into the north side of the city of Marion, where hail the size of golf balls occurred.

Isolated severe thunderstorm cells formed explosively during the late afternoon hours. The storms rapidly intensified into destructive hailstorms, producing golf ball to baseball size hail for sustained periods of time. During the evening, damaging winds became the main hazard as a bowing line of storms moved east-southeast across the Mount Vernon area. The storms formed in an extremely unstable air mass south of an outflow boundary that was generated from earlier storms well to the north. Strong daytime heating and high dew points in the mid 70's yielded mixed-layer capes around 5000 j/kg. Wind shear was adequate for organized storm structures. Effective shear values averaged around 30 knots.