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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. Several reports concerning the tornado and its setting had inaccurate surface analyses and incorrectly stated that the tornado had formed in cold air well west of a surface cyclone. Results are presented from a study of the event using 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. New 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 [from ≈250 degrees at an average speed of ≈59 mph (≈26 m s-1)], moving farther away from the cyclone with time; and d) the storm remained very close to the surface warm front. It is likely that the tornadic supercell remained isolated from other storms throughout its life. There was no singular feature of the meteorological setting that would explain the extreme character of the Tri-State tornado; however, as the supercell and dryline moved rapidly eastward, the northward advance 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, warm front, and dryline for more than three hours was extremely unusual. [ABSTRACT FROM AUTHOR]