Remembering the 1974 "Super Outbreak" 37 Years Later
by Jason Berry/ Lead Meteorologist
Update: April 3, 7:06pm ET
The worst tornado outbreak of the 20th century occurred 37 years ago to-date. Dubbed the "Super Outbreak," 148 tornadoes touch downed between 1:00 PM EST April 3rd and 4th, resulting in 315+ fatalities, over 5,000 injuries and an estimated $600+ million loss (in 1974 dollars). The combined path length of all the tornadoes was approximately 2,500 miles across 13 states in the Eastern U.S., marking the longest on record for a 24-hour period.
The outbreak was set in motion by a powerful spring time low pressure system, which had developed in the interior Plains two days earlier on April 1. To the east of this system, warm-moist air from the Gulf of Mexico was fed north by a strong warm front and low-level jet. Meanwhile, strong upper level winds associated with the jet stream drove cold, Canadian air south behind a sharp cold front. The contrasting temperatures associated with the two air masses served as the initial ingredients for strong thunderstorms late in the day April 3.
By the afternoon hours, clusters of rotating thunderstorms known as supercells were rapidly developing in the warm unstable environment ahead of the cold front. The worst of the outbreak occurred across the Ohio Valley between 4:30pm and 6:30pm Eastern Daylight Time, producing four of the six violent tornadoes.
The first F-5 of the day occurred in Xenia, Ohio near Cincinnati, producing winds over 260 mph on the Fujita Scale (now Enhanced Fujita Scale). The twister killed 34 people, injuring 1,150 more. In all, about one fourth of the city was destroyed, leaving 10,000 residents homeless.
Further to the north, a supercell thunderstorm produced a series of 9 tornadoes across Illinois and Indiana, including an F-4 near Monticello, Indiana. The twister was one of the longest and most destructive of the outbreak, killing 16 people and injuring another 400 across Northern Indiana. Damage from the Monticello tornado was estimated over 100 million dollars (420 million in today's dollars).
In the aftermath, Dr. Ted Fujita spent days assessing damage paths from several of the larger tornadoes. In doing so, he discovered that strong "twisting" from a parent thunderstorm's downdraft disrupted storm inflow. This allowed the initial tornado to dissipate, and another to immediately touch down approximately along the same path. This proved case for the Monticello tornado, where not one but two tornadoes contributed to the 121 mile damage path from southeast Benton to La Grange Counties.
To-date, the Super Outbreak remains the most severe convective weather episode on record in the continental United States. No other event has come close in both longevity and extent.
Rotating supercells associated with the 1974 "Super Outbreak" spawned several violent tornadoes, including the F-5 (pictured above) in Xenia, Ohio. Warm-moist air from the Gulf of Mexico and a strong upper level jet (below) helped initiate the outbreak. Courtesey: NOAA/ National Weather Service
Tornadoes touch downed in 13 states (below), marking the longest on record for a 24-hour period in the continental U.S. Courtesey: NOAA/ National Weather Service
