A tornado epidemic at the end of the season hit Illinois on Saturday, down at least 18 confirmed tornadoes and hurt more than two dozen people in the Prairie state. The surprise swarm of twisters marked the second plus Hit Illinois during a single calendar day recorded in December. The storm forecasting center had issued a "slight" risk of bad weather that morning, warning that "the development of afternoon thunderstorms in the area seems likely, with [wind] Shear … favor the discrete structures of supercell storms. Supercell thunderstorms are the most dangerous form, with tornado precursors rising upward currents. Two storms of monsters dispersed, one in west central Illinois and the other about 120 km east. The giant storms were flanked by small supercells on either side, their flying saucer-like clouds traveling hundreds of miles through the countryside northwest of St. Louis. The western cluster dropped a total of nine short tornadoes along the banks of the Illinois River from Beardstown to Havana. The same storm resulted in a photo shoot for a daredevil mallard hunt In Fulton County: Further east, a second band of damage was observed between Springfield and Bloomington, west of Effingham County. At least one person was injured by a tornado at Mason while their mobile home was tossed at 110 mph. The strongest tornado of the day probably hit Taylorville, which was sometimes half a mile wide, as it entered the city of 11,000. According to Fox Illinois, 26 people were taken to the Taylorville Memorial Hospital after being injured by a tornado. Six remain in critical condition. The windstorm also severely damaged 100 homes. Despite the unusual time of the year, the storm was well predicted – leaving residents plenty of time to escape. The lack of mortality is a story of success, reflecting the 41-minute lead time assigned by the National Weather Service in Lincoln prior to the tornado. The office chose to issue a rare "tornado emergency," warning of a "large tornado and confirmed destruction" in the direction of Taylorville. Despite the huge damage, the twister has not been evaluated yet, with storm surveys continuing throughout the region. However, it is possible that winds can reach 130 mph.
Three-dimensional radar scan of the Taylorville tornado, Saturday. (GR2 adapted by the author) From a meteorological point of view, the supercell had a manual structure with a corkscrew-shaped updraft rising to six miles high. Saturday storms developed in an environment characterized by insufficient solar heating but abundant shear and spin energy. It meant that everything that was shot would quickly rotate. Time-lapse video of the storm in Taylorville shows it well, with beautiful streaks on the rotating cloud carved cylindrically. Meanwhile, Taylorville had a chance of flurries Monday afternoon. December tornadoes are not uncommon. The United States actually has a second, albeit less impressive, peak of tornado activity in the middle or late fall. Cold air waves mark the shock of the seasons, announcing the arrival of a mass of winter air in the upper atmosphere. But Saturday's episode was at the next level. December tornadoes appear to be on the rise, although limited data are not known with certainty. Although the trend seems to reveal a noticeable increase in tornado activity in December since the beginning of accounting in 1950, it is feared that many tornadoes prior to 2000 have not been reported / accounted for due lack of cell phones, cameras and social media.
(Data from TornadoHistoryProject.com)