Tornado Categories & Ratings

Tornado Categories
Tornadoes are grouped in 3 general categories:

Weak
  • 88% of all tornadoes
  • Less than 5% of tornado fatalities
  • Lifetime 1 to 10 minutes
  • Winds less than 110 mph
Strong
  • 11% of all tornadoes
  • 30% of all fatalities
  • Lifetime 20 minutes or longer
  • Winds 110 to 205 mph
Violent
  • Less than 1% of all tornadoes
  • 70% of all fatalities
  • Lifetime can exceed 1 hour
  • Winds greater than 205 mph
Radar depiction of a classic supercell containing a violent tornado
Tornado Ratings
The original Fujita Scale was published in 1971. The scale was a set of wind estimates based on damage. Although the Fujita Scale itself ranges up to F12, the strongest possible tornadoes are in the first 6 categories F0 to F5 (originally estimated to be between 261 to 318 mph).

The scale's value was first used extensively during the survey of every tornado of the 1974 Super Outbreak. It became the mainstay in the U.S. for meteorologists, scientists, and engineers studying climatology and effects of tornadoes on structures. The Fujita Scale was also the basis for entering data into the central database containing records of every U.S. tornado after 1950.

Enhanced Fujita Scale
Observations following the violent tornadoes in Jarrel, Texas, in 1997 and Oklahoma City / Moore, Oklahoma, in 1999, pointed to the possibility that the Fujita Scale wind category estimates might be too high. After 4 years, through the joint efforts of the Wind Science and Engineering Research Center at Texas Tech University, meteorologists, civil engineers and the National Weather Service, the Enhanced Fujita Scale was developed, replacing the original scale in 2007 and improving the ranking process.