Much like Hurricanes, tornadoes have a classification system based on the intensity of the tornado. This scale is commonly known as the enhanced fujita scale (or EF-scale). Using a 0 to 5 scale, the EF scale ranks tornadoes based on their estimated wind speed. EF-0 being the weakest with minor damage, and EF-5 being the most severe damage.
However, you might be confused on how the tornadoes get their ratings. When did this system start? Why does it only go up to 5? Who started the scale? Why is there an F and an EF scale? All of these questions will be answered in this special blog post, diving into the history of the Fujita Scale, we can see where many of these answers come from.
TORNADO RATINGS PRIOR TO 1950
Until the 19th century, tornadoes were a phenomenon little thought of in the world. Sure, they happened in Europe and the east coast of the United States, but seldom thought of other as acts of God. It was not until settlement in the Great Plains in the 1840s onward brought settlers into contact with the violence of tornadoes on a more regular basis. The first real motion to study tornadoes came in the 1880s with a man named John Park Finley, who ventured to the Plains between 1880-1884 studying and classifying tornadoes. His research brought the United States into its first understanding of how tornadoes formed.
As quickly as this transformation was made, all progress into tornado research was placed to a screeching halt. With the advent of the US Weather Bureau in 1890 (the precursor to the National Weather Service), many felt discussing and forecasting tornadoes would only lead to panic among the public. Thus, from the mid-1890s onward, the word "tornado" was banned from public use. No tornado warnings, no tornado forecasts, and certainly no tornado ratings.
This ban was challenged on March 25, 1948, when two meteorologists at Tinker Air Force Base in Oklahoma City defied the Bureau. A tornado struck the base on March 20, and conditions appeared eerily similar just five days later. The two men, Robert Miller and Ernest Fawbush, decided to issue the first Tornado Warning for the base. Sure enough, just a few hours later a tornado tore across the base. The two men had founded the modern tornado warning system.
Even as tornado forecasting was becoming commonplace, rating tornadoes remained outside the new realm. As tornadoes continued to happen in the 1950s, the public wanted answers behind tornadoes as well as a way to classify them. Enter into the picture Dr. Tetsuya Theodore Fujita.
THE MAN BEHIND THE SCALE: THE LIFE OF DR. TED FUJITA
Born in Japan in 1920, Ted Fujita as he is more commonly known developed an interest in science from an early age. Going to college in the 1940s, Fujita lived through the war in Japan, surveying the remains of Nagasaki after the second nuke destroyed the city in August 1945. He soon got his masters degree in Japan in "weather science", and began correspondence with a professor from the University of Chicago Horace Byers. Byers was impressed, and eventually Fujita visited him in 1953. By the mid-1950s, Fujita now had a solid career as a meteorologist where he made strides in tornado environment research.
On June 20, 1957, a violent tornado struck Fargo, ND. Fujita went to the city to study the path of the tornado, and using over 150 photographs sent in from witnesses he was able to construct a detailed map of the tornado. Fujita also identified features common with tornadoes such as the "wall cloud". His work on the Fargo tornado cemented him as a tornado researcher in the eyes of the Weather Bureau, and he began studying tornadoes through the 1960s.
On April 11, 1965, a rash of tornadoes swept over the Midwest. 35 tornadoes tore through states like Michigan, Indiana, and Ohio in the "Palm Sunday Outbreak". Over the next few weeks, Fujita took aerial surveys of the tornado tracks and identified many features of these tornadoes. His major question when flying overhead was the discrepancies in damage he saw between tornadoes, where some caused minor damage while others wiped out whole towns. It was this outbreak which provided the impetus for his research into devising a scale to rank tornado damage.
In 1971, Fujita unveiled his new scale for tornado ratings. Originally, his scale went up through F-6 but was later revised to be a 0-5 scale. At first, his scale caused some controversy among meteorologists due to structural issues. However, the scale eventually caught on. By the later 1970s, most meteorologists were ranking tornadoes using the fujita scale. Today, it is the staple of tornado ratings.
April 3-4, 1974, has been given the moniker the "Super Outbreak", as over 100 tornadoes swept through Illinois, Indiana, Ohio, Kentucky, Tennessee, and Alabama. Until 2011, this was the most intense tornado outbreak on record. Fujita spent weeks flying over the tornado tracks, and provided details of each of the 150+ tornadoes which occurred on this day.
After diverging into a study of downbursts and microbursts, which was causing aviation accidents, Fujita continued his study of tornadoes. Fujita continued to study tornadoes as they came, the last major one he studied being the Plainfield, IL F-5. Ted Fujita died in 1998 at the age of 78 at his home in Chicago.
THE FUJITA SCALE
By using the damage which occurred after the fact, Fujita devised a method to use that damage to estimate the wind speeds that could cause damage like that. His classifications went thus:
F-0 - Light Damage (40 - 72mph): F-0 tornadoes are the most common, and often cause minor damage. Examples of F-0 damage include tree branches snapped, windows blown out, shingles removed from roofs, and sheds are significantly damaged.
F-1 - Moderate Damage (73 - 112mph): Behind F-0 tornadoes, F-1 are also weak and relatively common tornadoes. Examples of F-1 damage may include garage doors being blown in, siding torn off homes, mobile homes flipped or moved, trees and power poles snapped, and minor roof damage to homes. Cars can also be flipped in an F-1 tornado.
F-2 - Significant Damage (113 - 157mph): F-2 tornadoes and up are classified as "strong tornadoes" as the damage they can do is significant. Examples of F-2 damage include roofs removed from homes, interiors of homes damaged, cars tossed, mobile homes destroyed, damage to well-built structures.
F-3 - Severe Damage (158 - 206mph): F-3 tornadoes are classified as "strong tornadoes". Examples of F-3 damage includes roof and outside walls of homes blown away, leaving interior walls left; two-story homes lose their second floor; trees are uprooted; metal buildings sustain heavy damage; cars tossed far from where they originally were; and large vechicles such as tractors lifted.
F-4 - Devastating Damage (207 - 260mph): F-4 and F-5 tornadoes are classified as "violent tornadoes" for the high degree of damage they can cause. In an F-4, trees are debarked, cars not only thrown but mangled, homes swept away to their foundations, and small buildings are completely destroyed.
F-5 - Incredible Damage (260+ mph): F-5 tornadoes are extremely rare, but can cause unfathomable devastation. Frame homes are swept away, leaving only foundations remaining. Cars are mangled and tossed hundreds of yards away. Well-built metal buildings are completely destroyed. Ground is scoured from dirt and concrete.
THE ENHANCED FUJITA SCALE
Into the 2000s, it became clear a revision to the original Fujita scale was needed. In the early 2000s, a team of meteorologists and structural engineers gathered together to create a new scale which improves on Fujita's original scale. The result was the "Enhanced Fujita Scale", or known as the "EF-scale". The EF scale was unveiled and put into operation in 2007, and that is the scale we use today. Therefore, the difference between F and EF is more timing and minor wind differences.
Those wind differences are:
F-0 (40 - 72mph) —> EF-0 (65 - 85mph)
F-1 (73 - 112mph) —> EF-1 (86 - 110mph)
F-2 (113 - 157mph) —> EF-2 (111-135mph)
F-3 (158-206mph) —> EF-3 (136-165mph)
F-4 (207-260mph) —> EF-4 (166-200mph)
F-5 (261+mph) —> EF-5 (201+mph)
This was made to better reflect wind speed estimates on damage done to buildings, as this one used structural engineers to help with building designs. The other major change of the EF scale was to add more "damage indicators", or objects that can be damaged in a tornado, such as trees, crops, and other structures.
THE FUTURE OF THE FUJITA SCALE
While popular, the Enhanced Fujita scale has some shortcomings and brings controversy occasionally. Since the EF scale is rated on damage only, it needs to impact things that can be significantly damaged. If a tornado producing winds of over 200mph only impacts fields and farmland, there can only be so much damage done to crops, and that tornado is likely to be underrated. It also does not take into account wind speeds from radar data, as radar looks above the ground and not at the surface.
An example of a controversial rating of a tornado came with the El Reno, Oklahoma tornado on May 31, 2013. The tornado was the widest on record at 2.6 miles, beating out the Hallam NE tornado from 2004. Mobile doppler radars measured wind speeds approaching 300mph inside the tornado. However, the tornado mostly stayed over rural farmland, and thus not causing damage. So while measured wind speeds were well within the EF-5 range, the official rating of the tornado sits at EF-3.
As recent tornadoes such as Mayfield, Kentucky has shown, the EF scale might need further revision. At the typing of this blog post, the top minds in damage surveying are discussing another revision of the EF-scale. This new revision will add in more damage indicators such as water towers and churches, and revise tree data even further. This new scale is expected to be unveiled in the coming years.
