This image is courtesy of NOAA of the 199 F5 tornado that leveled the southwest suburbs of of Oklahoma City. EF scale established in February 2007.
The National Weather Service, working with experts skilled in engineering, developed an ehancement to document the historical damage category of the original Fujita (F) scale. It was not a surprisie to learn that Dr. Ted Fujita had anticpated a need to go beyond his original reserach work of the tornado intensity scale first used in 1971. His extensive field work was ground breaking on documenting the severity of tornado damage.
You may be interested in learning that the original tornado scale also included an assignment of what was called a P scale, referenced after Dr. Alan Pearson who was chief of the Storm Prediction Center at the time the F scale was implemented. The P scale was associated with the path and width of the tornado track.
NOAA meteorologists, working for the National Weather Service, are often accompanied by research experts from universities with departments of meteorology during assessments following strong, EF3 or greater tornadoes. A close inspection of the structure, not unlike a crime scene investigation, is conducted to determine strurctural integrity of a destroyed building. Cars airborne from a twister, wrapped around a tree, can be an indicator of winds of 200 mph or greater.
See more on the enhanced Fujita scale. There are a number of indicators used to make a final determination of the tornadoes intensity. in the case of the Oklahoma City tornado, the Severe Storm Laboratory had a Doppler on Wheels postioned to measure winds of greater than 300 mph in the Doppler velocity data.