Meteorological Analyses of the Tri-State Tornado Event of March 1925

Abstract

Severe thunderstorms occurred across portions of the central United States on 18 March 1925. The deadly, long-track Tri-State tornado was the most publicized storm event of 18 March and remains the most significant single tornado in the nation’s history. There has been only one formal paper regarding the Tri-State tornado and its meteorological setting. Results are presented from a recent study of the event that was done drawing upon all relevant Weather Bureau data that could be obtained. The storms of 18 March were associated with a rapidly moving, synoptic cyclone that was not unusually intense. There appear to be no outstanding aspects of the meteorological setting that would explain the extreme character of the Tri-State tornado. Surface analyses indicate: a) the tornado was produced by a long-lived supercell that developed very near the center of the cyclone, possibly at the intersection of a warm front and a distinct dryline; b) the south-to-north temperature gradient ahead of the cyclone was very pronounced due to cooling produced by early morning storms and precipitation; c) the tornadic supercell tracked east-northeastward very rapidly at about 60 to 65 mph (~28 ms-1), moving farther away from the cyclone with time; and d) the storm remained very close to the surface warm front. Previous reports concerning the tornado and its setting had inaccurate surface analyses and surface pressures, and incorrectly stated that the tornado had formed in cold air well west of the surface cyclone. As  the supercell and dryline moved rapidly eastward, the northward movement of the warm front kept the tornadic supercell within a very favorable storm environment for several hours. Apparently, this consistent, time and space concatenation of the supercell, the warm front, and the dryline for more than three hours was extremely unusual.