With killer tornadoes in half a dozen states in the last month, information about the effective force of each tornado has been thrown around, but few people use the terms properly and fewer still know what they mean.
The Fujita scale was first proposed in 1971 and suggested a rating system for tornadoes and hurricanes based on the wind strength and damage done by the tornado. Since the evaluation of damage cannot begin while the tornado is on the ground, it is improper to discuss a tornado as an F-anything in the midst of the storm.
After a super outbreak of tornadoes around Oklahoma City in 1997, the National Weather Service argued that the wind strength estimates for Fujita scale needed to be revised, resulting in the adoption of the Enhance Fujita Scale, or EF rating of storms.
For clarity, both the largest of the tornadoes to hit Alabama on April 27 and the May 22 tornado in Joplin, Mo., were believed to be EF-4 tornadoes. However, the Severe Storms Center reviews data from the events long after they happen and may change a storms classification based on debris patterns and other information collected over months.
For example, on Nov. 19, 1991, a storm hit Marion, Ill., that was initially classified as a microburst, a sudden downburst of straight-line winds. Six months later, the Storm Prediction Center had reclassified it to an EF-3 tornado.
According to the NWS, the EF scale functions from 0 to 5 and while in theory an F-6 tornado could have been possible under the original Fujita scale, the enhanced scale considers an EF-5 representative of total destruction. Since nothing goes beyond total destruction, a tornado greater than an EF-5 cannot exist.
Based on the EF scale, an EF-0 event represents winds of less than about 75 mph and would damage roofs and tree limbs. An EF-5 tornado would have winds in excess of 261 mph and include total or near total destruction of all types of construction.
Tornado terminology is often used incorrectly, but the most important thing to understand is that the classification will always come after the fact. Until the storm is over, the tornado has no EF rating at all.
Lucinda Gunnin cut her teeth as a reporter covering Illinois government as an intern in the statehouse pressroom. She now brings 20 years experience and insight to covering news.
