Tornadoes are classified using one of two systems, the Enhanced Fujita Scale and the National Weather Service.
The National Weather Service (NWS) has a very general method of categorizing tornadoes as weak, strong or violent. The factors considered include estimated wind speed and the length of time the tornado exists.
Enhanced Fujita Scale
The most commonly used method for classifying tornadoes is the Enhanced Fujita scale, named for the meteorologist who first developed it. It is difficult to accurately determine the wind speed inside a tornado. Therefore, the Enhanced Fujita scale estimates the strength of a tornado based upon the damage it causes instead of attempting to measure the actual wind speed. Storms are rated on a scale of EF-0 through EF-5.
- EF-0—Wind speed between 65 and 85 miles per hour—Minor roof damage, and downed trees and tree limbs.
- EF-1—Wind speed between 86 and 110 miles per hour—Severe roof damage or removal, and damage to mobile homes, exterior doors and windows
- EF-2—Wind speed between 111 and 135 miles per hour—Structural damage to even well-constructed homes and complete destruction of mobile homes. Cars may also be moved and trees uprooted.
- EF-3—Wind speed between 136 and 165 miles per hour—Complete destruction of weak structures and severe damage to well-built homes and larger buildings. Trains may be overturned.
- EF-4—Wind speed between 166 and 200 miles per hour—Complete destruction of homes and larger buildings. Cars and smaller objects become airborne.
- EF-5—Wind speed over 200 miles per hour—Catastrophic damage to all structures. Cars and other objects become missiles.
“National Weather Service Weather Forecast Office.” National Oceanographic and Atmospheric Administration. N.p., n.d. Web. 23 Jan. 2013. <http://www.crh.noaa.gov/lmk/preparedness/tornado_small/classify.php>.
“Enhanced Fujita Scale.” Weather Underground. N.p., n.d. Web. 23 Jan. 2013. <http://www.wunderground.com/resources/severe/fujita_scale.asp?MR=1>.