The 1974 Super Outbreak was one of the most intense tornado outbreaks on record, occurring on April 3–4, 1974, across much of the United States. It was one of the deadliest tornado outbreaks in U.S. history. It was also the most violent tornado outbreak ever recorded, with 30 violent (F4 or F5 rated) tornadoes confirmed. On April 3–4, there were 149 tornadoes confirmed in 13 U.S. states and the Canadian province of Ontario. In the United States, the tornadoes struck Illinois, Indiana, Michigan, Ohio, Kentucky, Tennessee, Alabama, Mississippi, Georgia, North Carolina, Virginia, West Virginia, and New York. The outbreak caused roughly $600 million USD (equivalent to $3.92 billion in 2025) in damage. The outbreak extensively damaged approximately 900 mi2 (2,331 km2) along a total combined path length of 2,600 mi (4,184 km). At one point, as many as 15 separate tornadoes were occurring simultaneously.
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 and in the United States until the 2011 Super Outbreak, the largest outbreak on record by number of tornadoes in a 24-hour period. 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 most intense tornado outbreak in recorded history.
Meteorological synopsis
A powerful springtime low pressure system developed across the North American Interior Plains on April 1. While moving into the Mississippi and Ohio Valley areas, a surge of unusually moist air intensified the storm further, while there were sharp temperature contrasts between both sides of the system. Officials at NOAA and in the National Weather Service forecast offices were expecting a severe weather outbreak on April 3, but not to the extent that ultimately occurred. Several F2 and F3 tornadoes had struck portions of the Ohio Valley and the South in a separate, earlier outbreak on April 1 and 2, which included three killer tornadoes in Kentucky, Alabama, and Tennessee. The town of Campbellsburg, northeast of Louisville, was hard-hit in this earlier outbreak, with a large portion of the town destroyed by an F3. Between the two outbreaks, an additional tornado was reported in Indiana in the early morning of April 3, several hours before the official start of the outbreak. On Wednesday, April 3, severe weather watches already were issued from the morning from south of the Great Lakes, while in portions of the Upper Midwest, snow was reported, with heavy rain falling across central Michigan and much of Ontario.
April 3
Morning setup and convection
By 12:00 UTC on April 3, a large-scale trough extended over most of the contiguous United States, with several modest shortwaves rotating around the broad base of the trough. The mid-latitude low-pressure center over Kansas continued to deepen to 980 mb (28.94 inHg), and wind speeds at the 850-mb level increased to 50 kn (58 mph) (25.7 m/s (93 km/h)) over portions of Louisiana, Mississippi, and Alabama. Due to significant moisture advection, destabilization rapidly proceeded apace; the warm front near the Gulf Coast dissipated and then redeveloped northward over the Ohio River valley. Consequently, CAPE levels in the region rose to 1,000 J/kg. However, a warm temperature plume in the elevated mixed layer kept thunderstorms from initiating at the surface. Meanwhile, a large mesoscale convective system (MCS) that had developed overnight in Arkansas continued to strengthen due to strong environmental lapse rates. Later in the day, strong daytime heating caused instability to further rise. By 18:00 UTC, CAPE values in excess of 2,500 J/kg were present over the lower Ohio and the Mississippi Valley. As wind speeds in the troposphere increased, Large-scale lifting overspread the warm sector. At the same time, the forward-propagating MCS spread into the Tennessee and Ohio valleys, where it evolved into the first of three main convection bands that produced tornadoes. This first convective band moved rapidly northeast, at times reaching speeds of about 60 kn (69 mph) (30.9 m/s (111 km/h)). However, thunderstorm activity, for the moment, remained mostly elevated in nature.
Afternoon supercells
By 16:30 UTC, the large MCS began to splinter into two sections: the southern part slowed, lagging into southeast Tennessee, while the northern part accelerated, reaching Pennsylvania by 19:30 UTC. The split was related to several factors, including a band of subsidence over eastern Kentucky and western West Virginia; local downslope winds over the Appalachians; and an inversion over the same area. These factors allowed the northern part of the MCS to accelerate due to efficient ducting, while the southern part slowed as the boundary layer warmed and moistened. Numerous surface-based supercells began to develop in the southern area, beginning with one that produced an F3 tornado at about 16:30 UTC near Cleveland, Tennessee. Meanwhile, a new band of scattered thunderstorms developed at 15:00 UTC over eastern Arkansas and Missouri; over the next four hours, this band became the focus for several intense supercells, starting in eastern Illinois and southern Indiana. In the wake of the MCS, backing low-level winds, rapid diurnal destabilization, and perhaps cool, mid-level advection had occurred over the warm sector, weakening the convective inhibition (CINH) layer, and favorable wind profiles bolstered helicity to over 230 m2/s²—a combination of factors conducive to tornadogenesis. Consequently, the storms increased in intensity and coverage as they moved into Illinois, Indiana, and northern Kentucky, producing several tornadoes, including the first F5 tornado of the day, at 19:20 UTC, near Depauw, Indiana. Several of the storms to form between 19:20 and 20:20 UTC became significant, long-lived supercells, producing many strong or violent tornadoes, including three F5s at Depauw; Xenia, Ohio; and Brandenburg, Kentucky. These storms formed the second of three convective bands to generate tornadoes.
While violent tornado activity increased over the warm sector, a third band of convection developed at about 16:00 UTC and extended from near St. Louis into west-central Illinois. Based upon real-time satellite imagery and model data, differential positive vorticity advection coincided with the left exit region of an upper-level jet streak which reached wind speeds of up to 130 kn (150 mph) (66.9 m/s (241 km/h)), thereby enhancing thunderstorm growth. Storms grew rapidly in height and extent, producing baseball-sized hail by 17:20 UTC in Illinois and, shortly thereafter, in St. Louis, Missouri, which reported a very severe thunderstorm early in the afternoon that, while not producing a tornado, was the costliest storm to hit the city up to that time. By 19:50 UTC, supercells producing F3 tornadoes hit the Decatur and Normal areas in Illinois. As thunderstorms moved into the warmer, moister air mass over eastern Illinois and Indiana, they produced longer-lived tornadoes—one of which began near Otterbein and ended near Valentine in Indiana, a distance of 121 miles (195 km).
Continued activity
Meanwhile, by 00:00 UTC the southern half of the first convective band became indistinguishable from new convection that had formed farther south over Alabama and Tennessee in connection with convective band two. In this area, increasing west-southwesterly wind shear at all levels of the troposphere, juxtaposed over near-parallel outflow boundaries, allowed successive supercells, all producing strong, long-tracked tornadoes, to develop unconstrained by their outflow in a broad region from eastern Mississippi to southern Tennessee. These storms, forming after 23:00 UTC, produced some of the most powerful tornadoes of the outbreak, including a large and long-tracked F4 that struck the western and central portions of Alabama, tracking for just over 110 miles (180 km), two F5s that both slammed into Tanner, causing extensive fatalities, an extremely potent F5 that devastated Guin in Alabama, and multiple violent, deadly tornadoes that affected and caused fatalities in Tennessee.
April 4
Michigan was not hit as hard as neighboring states or Windsor, although one deadly tornado hit near Coldwater and Hillsdale, killing people in mobile homes; however, thunderstorm downpours caused flash floods, and north of the warm front in the Upper Peninsula, heavy snowfall was reported. Activity in the south moved towards the Appalachians overnight and produced the final tornadoes across the southeast during the morning of April 4. A series of studies by Dr. Tetsuya T. Fujita in 1974–75—which were later cited in a 2004 survey by Risk Management Solutions—found that three-quarters of all tornadoes in the 1974 Super Outbreak were produced by 30 'families' of tornadoes—multiple tornadoes spawned in succession by a single thunderstorm cell. The majority of these were long-lived and long-tracked individual supercells.
Confirmed tornadoes
- Note: An F3 tornado was confirmed in Ontario.
This tornado outbreak produced the most violent (F4 and F5) tornadoes ever observed in a single tornado outbreak. There were seven F5 tornadoes and 23 F4 tornadoes. More than 100 tornadoes associated with 33 tornado families. The first tornado of the outbreak is disputed, with some sources indicating an isolated F2 in Indiana at 13:30 UTC while Fujita marked the outbreak's onset at 18:10 UTC with an F0 in Illinois. As the storm system moved east where daytime heating had made the air more unstable, the tornadoes grew more intense. A tornado that struck near Monticello, Indiana, was an F4 and had a path length of 121 miles (195 km), the longest path length of any tornado for this outbreak. A total of 19 people were killed in this tornado. The first F5 tornado of the day struck the city of Depauw, Indiana, at 3:20 pm EDT. It killed 6 and injured 86 others along its 65-mile path, leveling and sweeping away homes in Depauw and Daisy Hill.
Seven F5 tornadoes were observed—one each in Indiana, Ohio, and Kentucky, three in Alabama, and the final one which crossed through parts of Indiana, Ohio, and Kentucky. Thirty-one people were killed in Brandenburg, Kentucky, and 28 died in Guin, Alabama. An F3 tornado also occurred in Windsor, Ontario, Canada, killing nine and injuring 30 others there, all of them at the former Windsor Curling Club.
There were 18 hours of nearly continuous tornado activity that ended in Caldwell County, North Carolina, at about 7:00 am on April 4. A total of 319 were killed in 148 tornadoes from April 3 through April 4 and 5,484 were injured.
The 1974 Super Outbreak occurred at the end of a very strong, nearly record-setting La Niña event. The 1973–74 La Niña was just as strong as the 1998–99 La Niña. Despite the apparent connection between La Niña and two of the largest tornado outbreaks in United States history, no definitive linkage exists between La Niña and this outbreak or tornado activity in general. Some tornado myths were soundly debunked (not necessarily for the first time) by tornado activity during the outbreak.
The most prolific and longest-lasting tornado family of the outbreak tracked from central Illinois and the entirety of northern Indiana from 2:47 p.m. to 6:59 p.m. (UTC−05:00), a span of 4 hours and 12 minutes. Eight tornadoes touched down, including the longest-tracked single tornado of the outbreak: the 121 mi (195 km) F4 Monticello tornado. However, that tornado may itself have been composed of three individual F4 tornadoes.
Depauw–Martinsburg–Daisy Hill, Indiana
This was the first in a series of five consecutive violent tornadoes produced by a single supercell from southern Indiana into extreme northern Kentucky and then southwestern Ohio. It was also the first F5 tornado out of the seven during the outbreak. The tornado initially touched down south of Huffman around 2:16 p.m. CDT and moved along an east-northeast to northeast path. One person died near the origin point when their mobile home was destroyed. Southeast of Branchville, one person died and another was injured while sheltering in a ditch. The bus they were previously in was thrown 50 ft (15 m) into the ditch and crushed them. In Crawford County, the tornado grew to over 1 mi (1.6 km). It skirted by several smaller communities but completely destroyed many rural farms. It struck southeastern portions of Depauw, killing one person. While moving through Depauw, no condensation funnel was observed with the tornado despite its intensity and remained that way as it moved into Martinsburg. Another person was killed east of Palmyra. In Washington County, the tornado moved directly through Martinsburg, destroying 38 out of 48 homes in the town. The Indianapolis News described the town as "for all practical purposes is no longer there". Numerous trees were completely stripped of their branches and debarked. The tornado soon struck Daisy Hill where several homes were completely swept away. It ultimately dissipated near New Liberty around 3:25 p.m. CDT after traveling 62 mi (100 km).