Behind the Forecast: How tornadoes are rated

Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.

Science Behind the Forecast: Tornado Ratings

LOUISVILLE, Ky. (WAVE) - Tornadoes are some of the most destructive storms on the planet. They can range from just a few yards to more than a mile wide. Some may be nearly stationary while others can travel at higher than highway speeds. A tornado's size isn't necessarily indicative of its strength. In their aftermath, the National Weather Service's (NWS) meteorologists are tasked is to rate these potentially deadly and devastating storms.

Tornadoes are classified based on their estimated wind speed and the damage they cause.

Weak EF0, EF1 Wind speeds of 65 to 110 mph
Strong EF2, EF3 Wind speeds of 111 to 165 mph
Violent EF4, EF5 Wind speeds of 166 to 200 mph or more
March 2, 2012 in Henryville, Indiana is a day that is hard for residents to forget after a tornado devastated the area and destroyed part of the community’s high school.
March 2, 2012 in Henryville, Indiana is a day that is hard for residents to forget after a tornado devastated the area and destroyed part of the community’s high school. (Source: Henryville High School)

For more than 30 years before 2007, the F-Scale, created by Dr. Theodore (Ted) Fujita, was used worldwide to estimate a tornado’s strength and wind speed. The Enhanced F-Scale (EF Scale) is now used to rate tornadoes. The Enhanced Fujita (EF) Scale was created by a group of meteorologists and engineers assembled by the Wind Science and Engineering Research Center at Texas Tech University. The EF Scale uses estimates of three-second gusts at the point where the damage occurred. The estimates can vary with height and exposure to the elements. Keep in mind that the three-second wind gusts are different from the standard measurements taken by weather stations; those use a directly measured “one-minute-mile” speed.

EF Number
3 Second Gust (mph)
0 65 to 85
1 86 to 110
2 111 to 135
3 136 to 165
4 166 to 200
5 Over 200

The EF Scale has a more accurate range of wind speeds compared to the F-Scale, according to the National Weather Service.

Original F Scale Enhanced F Scale
Rating 3 Second Gust Speed (mph) Rating 3 Second Gust Speed (mph)
F 0 45-78 EF 0 65-85
F 1 79-117 EF 1 86-110
F 2 118-161 EF 2 111-135
F 3 162-209 EF 3 136-165
F 4 210-261 EF 4 166-200
F 5 262-317 EF 5 Over 200

The actual wind speeds in most tornadoes are not known, and the wind needed to do similar-looking damage can vary greatly, even from building to building, according to the National Weather Service. Due to this, wind speeds on the EF Scale are acquired from engineering guidelines and are only estimates. The NWS is the only federal agency that can provide an official tornado rating.

On a damage survey, meteorologists must uncover where the tornado initially touched down, its width, strength and where it lifted. They must also determine whether the damage was caused by a tornado or straight-line winds. The NWS says that a survey team is typically equipped with a GPS unit, a cell phone, a laptop with damage survey software, a digital camera, an atlas or gazetteer, and a notebook. While damage is usually surveyed by the ground, sometimes an aerial survey is conducted.

Copyright 2020 WAVE 3 News. All rights reserved.