The “Super Outbreak of April 3-4, 1974” occurred across portions of the Midwest, Lower Mississippi Valley, and Southeast. In what was the worst tornado outbreak of the 20th century, there were 148 tornadoes over the course of just 18 hours, over half of which were classified as significant/strong at F2 strength or higher.
Many comparisons have been made between this outbreak and the April 25-28, 2011 outbreak which featured 358 tornadoes. Although the more recent outbreak featured many more tornadoes, they occurred over a longer time period in an age of better tornado detection, and the worst was confined to a smaller area compared to April 3-4, 1974.
Perhaps the most staggering fact from the 1974 outbreak was the amount of F4 and F5 tornadoes; an incredible 30 (23 F4s and 7 F5s). The 1974 outbreak featured 30 violent tornadoes in less than one day when the national average is only about 7 per year.
The chart above displays a comparison of the most intense tornadoes (F/EF3 or higher) between the 1974 and 2011 outbreaks. In all of these categories, 1974 prevails with ease. Tony Lyza provided a more detailed numerical breakdown comparing the number of significant tornadoes between the 1974 and 2011 outbreaks in a post last year.
The April 1974 outbreak has been reviewed, discussed, and analyzed ad nauseum throughout the meteorological community over the years: from the meteorological set-up, to climatological comparisons, to NOAA and National Weather Service reviews.
This article looks at the April 1974 outbreak from a different, visual perspective. I use maps to first look at the event from the past, then present the same information with a fresh face using some thought-provoking interactions and overlays.
The First Super Outbreak Map Ever Made
The first map ever made of the April 3-4, 1974 event was done by the renowned Ted Fujita when he was affiliated with the University of Chicago. He personally surveyed most of the tornado paths and produced this hand-drawn map with impressive detail and acuity.
Popular Maps of the Event
As already mentioned, meteorologists have been studying this event for close to 40 years. Below are maps from NOAA and the Tornado History Project that are popular resources and available to the public. Both maps are great visual representations of the event, as they symbolize the individual tornado tracks rated according to the Fujita Scale.
Both maps above provide a good reference of the spatial distribution of the tornadoes as well as distribution of the different tornado strengths. The greatest concentration of tornadoes occurred over portions of Indiana, Ohio, Kentucky, and Tennessee.
All seven F5 tornadoes occurred on the 3rd, and Alabama was the state that experienced the highest number of F5 tornadoes that day; three out of seven. The other F5 tornadoes occurred throughout Kentucky, Indiana, and Ohio. Here is the final confirmed tornado count and breakdown according to Fujita categories:
And here is a chart showing the distribution of tornadoes by state; 13 states total. Tennessee experienced the most tornadoes out of any other state, with 37.
The first map interaction involves overlaying the tornado tracks symbolized according to the my color scheme above (see legend) on top of Ted Fujita’s original tracks. Adding the color information helps enhance Fujita’s hand-drawn tracks while still maintaining the historical map feel.
Here is a zoomed in version of the same map:
A second map interaction of interest investigates a “what if this happened tomorrow?” scenario. In other words, given the current population distribution and the urban sprawl around major population centers what areas would be hardest hit if this same outbreak happened today?
The map below involved overlaying urban areas according to the 2010 Census on top of Ted Fujita’s original track map.
While U.S. population has not necessary exploded since 1974, urban sprawl has undoubtedly become more prevalent. By looking at the map, it is easy to see which urban areas would be devastated if this outbreak occurred today.
On the northern edge of the outbreak Decatur, Illinois and the suburbs of Cincinnati, Ohio are hit hard. On the eastern edge of the outbreak area Roanoke, Virginia, a city which has significantly expanded both in size and population since 1974, would experience major damage from the tornado that struck the town in the early hours of the 4th.
Moving south across Kentucky, the northern suburbs of Louisville and southern suburbs of Lexington are impacted; these areas of Kentucky were hit hard by the March 2nd, 2012 outbreak. Moving south still, the suburbs of Nashville are devastated by multiple tornadoes. Finally, at the southern edge, Hunstville, Alabama would likely sustain catastrophic damage from one of the long-track F5 tornadoes.
Here’s a zoomed in version of the map to better see some of the urban areas:
For at least certain benchmarks, the Super Outbreak of April 3-4, 1974 remains as THE tornado outbreak that all other tornado outbreaks are compared to. April 25-28, 2011 was compared to 1974 in terms of the atmospheric set-up (both occurred in a La Nina pattern) and also compared in the number, spatial distribution, and intensity of the tornadoes.
Given the ferocity and destruction associated with these large-scale tornado outbreaks, tornado researchers wonder if these events will remain as once-in-a-generation events, or if they will happen more (or less) frequently. In a country that experiences 75% of the world’s tornadoes each year, it is well worth reviewing these big outbreaks on their anniversaries.
NWS Survey report: http://www.april31974.com/TornOut.pdf
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