The 1974 Super Outbreak

The 1974 Super Outbreak was the second-largest tornado outbreak on record for a single 24-hour period, just behind the 2011 Super Outbreak. It was also the most violent tornado outbreak ever recorded, with 30 F4/F5 tornadoes confirmed. From April 3–4, 1974, there were 148 tornadoes confirmed in 13 U.S. states and the Canadian province of Ontario.[nb 1] In the United States, tornadoes struck Illinois, Indiana, Michigan, Ohio, Kentucky, Tennessee, Alabama, Mississippi, Georgia, North Carolina, Virginia, West Virginia, and New York. The outbreak caused roughly $843 million USD (equivalent to $5.21 billion in 2023) in damage, with more than $600 million (equivalent to $3.71 billion in 2023) occurring in the United States. The outbreak extensively damaged approximately 900 sq mi (2,331 km2) along a total combined path length of 2,600 mi (4,184 km).[2][3] At one point, as many as 15 separate tornadoes were occurring simultaneously.[2][4]

The 1974 Super Outbreak was the first tornado outbreak in recorded history to produce more than 100 tornadoes in under a 24-hour period, a feat that was not repeated globally until the 1981 United Kingdom tornado outbreak[5] and in the United States until the 2011 Super Outbreak. In 2023, tornado expert Thomas P. Grazulis created the outbreak intensity score (OIS) as a way to rank various tornado outbreaks. The 1974 Super Outbreak received an OIS of 578, making it the worst and most violent tornado outbreak in recorded history.[6]