There were 148 tornadoes that occurred in a 24 hour period from 1:00 PM EST April 3rd to 1:00 PM EST on April 4 th. The combined path length of all tornadoes during this period was approximately 2500 miles with 315+ fatalities, over 5000 injuries, and an estimated $600+ million loss (in 1974 dollars). Not only was the eastern US devastated by tornadoes, but high winds and very large hail accompanied many thunderstorms that day. The worst tornado outbreak of the 20th century hit Indiana hardest on April 3, 1974.
One of the most destructive tornadoes (including the longest path length) of any tornado during the outbreak was the Monticello Indiana Tornado. The Monticello Tornado was spawned by an intense supercell thunderstorm. The same thunderstorm produced a series of 9 tornadoes across Illinois and Indiana, known as the Monticello tornado family. Tornadoes included in the Monticello tornado family were: Owaneco, Pierson, Tolono, Homer Lake, and Bismarck in Illinois with Rainsville, Otterbein (originally classified as part of the Monticello tornado track), Monticello, and Plato in Indiana (tornadoes 7-14 in the figure below). The Monticello tornado family was responsible for 18 deaths across Illinois and Indiana, several injuries, and an enormous amount of damage in excess of $100 million (1974 dollars).
The Monticello tornado was originally rated as having an impressive 121 mile path length from southeast Benton County to La Grange County (IN). However, further analysis and research by Dr. Ted Fujita indicated that this was not the case and the Monticello tornado was officially reclassified as two separate tornadoes. Dr. Fujita discovered that a strong “twisting” downdraft from the parent thunderstorm (most likely the thunderstorm’s rear flank downdraft) disrupted the storm’s inflow, subsequently allowing the initial tornado to dissipate. As soon as the first tornado dissipated, another touched down almost immediately and nearly along the same path. So, to the casual observer it appeared as a single tornado track. In reality, as the first of the tornado lifted, the second touched down, just west of Brookston. The reclassification of the tornado still documents the Monticello Tornado as having a 109 mile path length with a path width of up to a half mile, retaining the title as the longest track tornado during the Super Outbreak of 1974.
Information for the post comes the National Weather Service Northern Indiana Forecast Office.