Buzz
An F5 tornado approached Oklahoma City on May 3, 1999. Image courtesy of NSSL NOAA via Flickr | CC BY-ND 2.0
Tornadoes are a frightening reality in the United States. The country sits in the most tornado-prone area in the world. Even though more than a thousand tornadoes occur annually, accurately measuring the winds in a typical tornado remains nearly impossible.
A brilliant meteorologist, Tetsuya “Ted” Fujita, found a way to overcome this challenge by developing an innovative method to estimate the wind speeds of tornadoes based on the destruction they leave behind, leading to the creation of the Fujita Scale. Below are 10 important facts about the Fujita Scale, which helps us gain a clearer understanding of the most powerful storms nature can unleash.
1. FROM ZERO TO FIVE
Dennis Mersereau
Both the original Fujita Scale (1973–2007) and the current Enhanced Fujita Scale assess tornadoes on a scale from zero to five, with five representing the most catastrophic tornadoes. While the images of vast, mile-wide twisters ripping through Oklahoma are etched in our memories, most tornadoes are relatively small and weak, falling at the lower end of the scale. Of the 60,114 tornadoes recorded from 1950 to 2015, 80 percent were rated as F0 or F1 on the old scale, or EF-0 or EF-1 on the new scale. This is in stark contrast to the 60 F5 or EF-5 tornadoes recorded since 1950.
2. THE SURVEY SAYS …
Meteorologists determine tornado ratings by conducting surveys of the damage caused, both from the ground and from the air, to assess the width and length of the tornado’s path. They also examine the debris patterns to confirm the presence of a tornado (as opposed to straight-line winds) and inspect the damage to homes, businesses, and vegetation to estimate the strength of the tornado’s winds at specific points along its route.
3. THE SCALE WAS “ENHANCED” IN 2007.
For over 35 years, the National Weather Service used the original Fujita scale (and even retroactively rated tornadoes back to 1950), but meteorologists and engineers discovered that it often overestimated the strength of tornadoes. The new Enhanced Fujita Scale accounts for the quality of buildings when determining ratings, which makes a significant difference. A tornado that destroyed a house built in 1940 likely had weaker winds than one that took down a similar house built in 2015. Including construction standards allows meteorologists to better assess a tornado's true strength.
4. ENGINEERING PLAYS A CRUCIAL ROLE IN THESE RATINGS.
The Enhanced Fujita Scale is not just about meteorology; it's also a matter of engineering. Meteorologists and engineers collaborated to determine how strong winds must be to cause various levels of damage. They use 28 different categories to evaluate damage to everything from trees and barns to solid structures like schools or prisons. For instance, a tornado that causes the walls of a retail store like Walmart to collapse would likely be rated EF-3, with winds reaching nearly 140 mph.
If a tornado were to hit a hospital and cause total structural deformation, the wind speeds would likely exceed 200 mph, classifying it as an EF-5. This occurred in Joplin, Missouri in May 2011 when a massive, mile-wide tornado struck the St. John’s Regional Medical Center, severely damaging the nine-story hospital and its foundation. Almost 160 people were killed in the Joplin area as a result.
5. THE SCALE IS ONLY USED TO ASSESS DAMAGE.
An EF-5 tornado knocked over these street signs in Moore, Oklahoma, in May 2013. Image credit: US Air Force via Flickr
The Enhanced Fujita Scale only evaluates the damage left behind by tornadoes. A massive tornado that devastates open fields in Kansas could still receive an EF-0 rating, even if its winds were significantly stronger—if it didn’t damage structures or trees, there would be no way to accurately assess its strength.
6. FINDING EF-5 DAMAGE IS EXTREMELY CHALLENGING.
Meteorologists often face difficulty identifying damage severe enough to classify a tornado as an EF-5. There are very few structures capable of surviving winds close to 200 mph, and the evidence of such winds can easily be buried beneath layers of debris.
7. SOME RATINGS SPARK DEBATE.
The rating assigned to a powerful tornado can sometimes spark debates over whether it was stronger or weaker than originally thought. Many of these disagreements arise because EF-5 damage is so incredibly difficult to detect.
The largest tornado ever recorded touched down in El Reno, Oklahoma, in May 2013. This 2.5-mile-wide behemoth sparked one of the most hotly debated ratings in recent history. A nearby mobile Doppler radar recorded winds inside the tornado reaching nearly 300 mph. Initially, these measurements were used to assign the tornado an EF-5 rating. However, despite the high winds, the National Weather Service later revised the tornado’s rating to EF-3 because it didn’t cause any EF-5 level damage.
8. THERE IS NO EF-6.
After a devastating tornado, there’s often debate about whether we should introduce an EF-6 category to account for the absolute worst tornadoes. Much like the Saffir-Simpson Scale used to classify hurricanes, the Enhanced Fujita Scale currently lacks an upper limit. The destruction caused by an EF-5 tornado is so total and catastrophic that there is no need for a higher rating.
9. TWO DEADLY DAYS, HUNDREDS OF TORNADOES
An aerial view of the destruction caused by the EF-5 tornado that passed through Hackleburg, Alabama, on April 27, 2011. Image credit: NWS Birmingham
One catastrophic tornado is terrifying enough, but there have been instances where multiple destructive tornadoes have struck simultaneously. Two specific days in modern history stand out. The first was the Super Outbreak of April 3, 1974, which saw 148 tornadoes ravage the Midwest, including 23 rated F4 and seven rated F5.
The second major outbreak occurred on April 27, 2011, when an unprecedented 219 tornadoes—among them 11 EF-4s and four EF-5s—ripped through the Southeast in a single day, claiming the lives of over 300 people and injuring thousands.
10. FUJITA'S RESEARCH INTO SEVERE WEATHER EXTENDED FAR BEYOND TORNADOES.
If you've ever flown during severe weather, Fujita’s research helped ensure your safety. Beyond his work on the tornado scale and other studies, Fujita’s investigations into microbursts were pivotal in enhancing aviation safety. Microbursts are sudden, intense downward gusts from thunderstorms, and have been the cause of some of the deadliest plane crashes in U.S. history. Fujita’s findings were instrumental in the development of technology that enables aviation experts to detect and avoid these hazardous events.
