The "Tri-State tornado" event of 18 March 1925, with an official death toll of 695 people, generally is accepted as the deadliest single tornado in United States recorded history.? The officially accepted damage path is 352 km (219 mi) long.? The entire damage path was not surveyed by the Weather Bureau in 1925 to determine if it truly was continuous, and the nature of the tornado event and the storm that produced it are not well known.? Therefore, as much new data as possible have been gathered about this event in all three states along and near the purported damage path.? Detailed information about the locations where damage was reported and the type of damage (recorded as "damage points") was obtained from: interviews and driving surveys with first- and secondhand eyewitnesses, many local 1925 and later newspapers, local books, and photographs and other materials found in local libraries and genealogy centers. ? After plotting all damage points, a potential damage path of 378 km (235 mi) was indicated.? However, 32 gaps ≥1.6 km (1 mi) appeared between consecutive damage points.? This paper presents all the damage points, and indicates which of the gaps might be "real" (i.e., where one tornado ended and another tornado developed), as well as those gaps more likely to have been a continuous tornado. ?We speculate that path segments at the beginning of the potential damage path in eastern Shannon County, MO, and at the end of the potential path in central Pike County, IN, were both likely from separate tornadoes. ?In the very rural and hilly terrain of southeast Missouri, there were areas with a minimum of human development and no known witnesses to the tornado (parts of Reynolds, Iron and Madison Counties). This led to several relatively long damage path gaps >3.2 km (2 mi). ?The existence of relatively long?gaps prevents confidence in the continuity of the first section of the path.? Beginning in central Madison County, MO, and continuing to Pike County, IN, a distance of 280 km (174 mi), there are no gaps >3.2 km (2 mi), more strongly suggesting that the tornado was likely continuous for that path segment.? Because of having the highest density of damage reports and the most eyewitness reports, the part of the main damage path that is 243 km (151?mi) long from central Bollinger County, MO to the west edge of Pike County, IN can be considered likely a continuous path.? The tornado event was associated with what began as a classic supercell in Missouri, transitioning to high-precipitation mode in Illinois and Indiana.? Witnesses saw a wedge tornado along most of the damage path and a large multivortex tornado in some areas.? At two places in Illinois, a satellite tornado may have appeared at about the same time as the primary tornado was passing nearby. ?Another previously unreported tornado with a 32-km (20-mi) damage path occurred in Washington and Jackson Counties, IN, whose path and trajectory suggests that it may also have been produced by the same supercell.? This new tornado started about 75 min later and about 105 km (65 mi) east-northeast of the apparent end of the Tri-State tornado damage path in Pike County, IN.
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