□ The Super Outbreak of 1974 was deemed by many as a once in 500 year event. Then the 2011 Super Outbreak tore through the Deep South and suddenly the “once in many lifetimes” outbreak didn’t seem quite so unprecedented. With less than a century’s worth of solid corroborative evidence, the frequency of mega-outbreaks is unknown and potentially dramatically understated.
Looking at the official statistics, the two outbreaks are very comparable. The 2011 outbreak had more tornadoes, yet technology in 1974 was liable to miss some of the briefer touchdowns. The 2011 outbreak probably had more tornadoes overall, but the difference is probably minimal.
Many believe that the 1974 tornado outbreak remains the most violent in history due to the greater number of E/F3, E/F4 and E/F5 tornadoes. In raw numbers, we see the following:
Event: April 3, 1974 April 27, 2011
E/F3 35 20
E/F4 24 11
E/F5 6* 4
*The second tornado that devastated Tanner, Alabama, has since been upgraded to an F5 on most official publications without any detailed explanation. Fujita surveyed the tornado’s path and awarded an F4 rating.
The 1974 outbreak had 65 strong tornadoes, whereas the 2011 outbreak had 35. Taken at face value, the 1974 outbreak appears the most violent of the two. Even so, the 2011 outbreak caused slightly more fatalities (325 vs 319) and had single-tornado death tolls significantly higher than the 1974 outbreak despite advancements in tornado warning and lead time.
One potential variable to explain these inconsistencies is changes in the rating standards. A contemporary EF5 rating is more difficult to attain than an F5 rating 30 years ago. If the 1974 tornado outbreak was evaluated using the Enhanced Fujita Scale, the number of tornadoes given an EF5 rating would undoubtably be less than six. With the Enhanced Fujita Scale, a tornado has to do more than simply sweep a house from its foundation to achieve an EF5 rating. The obliterated home now must be of superior construction – a standard above the “normal” or “typical” construction standard often used to rate F5’s in the 1970’s.
The 1974 outbreak has achieved mythical status through years of telling and retelling. While the outbreak was exceedingly violent, some of its more famous tornadoes were not as uncommonly intense as sometimes portrayed. A good example is the Xenia, Ohio, F5 tornado. Books in the 70’s refer to the Xenia tornado as “the strongest tornado ever recorded,” and online discussions bring forward claims that Prof. Fujita himself “considered rating the Xenia tornado an F6.” This often repeated claim has no basis in reality. Most of the damage caused by the Xenia tornado was in the F2 to F3 range. The only area where homes were swept from their foundations appears to be in the subdivisions on the western edge of town near the I-35. Most of the damage in the city could have been caused by winds under F4 intensity.
The Xenia tornado would probably have received an EF5 rating today based on the damage in Windsor Park, but most of the damage through the center of town was of EF3 intensity. If any tornado in the 1974 outbreak were to be deemed the “most powerful”, the Brandenburg, Kentucky, tornado would be a logical contender as it scoured vegetation from the ground and swept away more than a dozen large, well-built homes.
If the more stringent Enhanced Fujita Scale had been used back in 1974, the number of EF5 tornadoes would likely have been four or less. The Sayler Park and Depauw tornadoes both caused minimal F5 damage to homes of modest construction. Using the EF-Scale, it is almost certain that these two tornadoes would have received an EF4 rating. If the situation was reversed and the 2011 outbreak was analyzed using 1974 standards, it is likely the Tuscaloosa tornado, the Arab tornado and the Ringgold tornado would have been awarded F5 ratings. Other tornadoes in the 2011 outbreak also swept seemingly well-built homes from their foundations in classic F5 fashion including the Shoal Creek tornado, the Cordova tornado and the Dekalb County/Trenton tornado. Overall, comparing the two outbreaks is challenging due to changes in damage scale implementation. As many as seven to ten tornadoes in the 2011 outbreak caused damage indicative of F5 intensity.
Another method to ascertain tornado violence is the death to injury ratio. The notion holds that the more violent the tornado, the greater the fatality rate above-ground. There were approximately 5,400 injuries in the 1974 event, whereas the 2011 outbreak caused more deaths yet fewer than half the injuries. The Tuscaloosa tornado and the Xenia tornado caused a similar number of injuries (approximately 1,000) but the Tuscaloosa tornado killed twice as many people. Even though variations exist (more homes have basements in Ohio and more homes were damaged over a longer path-length in Tuscaloosa), the injury to death ratio indicates that the Tuscaloosa tornado, on average, was more difficult for those above ground to survive. This is even more true for some of the other EF5’s in 2011, particularly the incredibly powerful Phil Campbell tornado, which caused 72 deaths and only 145 injuries. Furthermore, almost all of the 2011 fatalities occurred during daylight hours whereas more than a third of the 1974 deaths occurred at night. An article by Stimers and Paul (2011) noted that tornado fatality rates increase by 56% during the overnight hours.
A possible explanation for the greater number of fatalities in 2011 may be the intensity of the deadliest tornadoes. The strongest tornadoes in the 2011 Super Outbreak were measurably more intense than all but one or two of the 1974 tornadoes, or at least when they impacted populated areas. The four EF5’s in 2011 caused some of the most extreme tornado damage ever photographed. Another variable may be just plain luck. Both outbreaks struck populated areas, but some areas are more vulnerable than others.
Overall, the two outbreaks were very similar. Both had dozens of violent and fast moving tornadoes and both were unprecedented in their respective era. Some argue that the 1974 Super Outbreak remains the most violent on record, but the higher number of fatalities in 2011 and the stricter rating standards utilized by the Enhanced Fujita Scale call such a conclusion into question.