On the night of May 4, 2007, at approximately 9:45 pm, the rural town of Greensburg, Kansas, was tragically struck by a 2.7 km wide EF5 tornado. The twister caused 11 fatalities and destroyed 95% of the buildings in the town of 1500 people, packing estimated winds as high as 205 mph according to the National Weather Service (NWS). It was the first time that any tornado had been given an EF5 rating on the new Enhanced Fujita Scale since its implementation in February of 2007, and the first tornado to earn an F5 or EF5 rating since the Moore, OK tornado of May 3, 1999. In this month’s article, we’ll examine why the Fujita scale was “Enhanced”, and take a look to see how Greensburg is rebuilding one year after the deadly storm.
The original Fujita scale was pioneered in 1971 by Dr. Ted Fujita, as a means of classifying tornadoes according to the damage they caused. Fujita designed it so that the ranges of wind speed in various F-levels would smoothly connect the Beaufort Scale (a 0 to 12 scale that measures wind speed based on observed ocean conditions) and the Mach number scale (which defines speeds relative to the speed of sound). F0 and F1 corresponded to Beaufort Scale number 8 and 12 respectively, and F11 and F12 corresponded to Mach 0.9 and Mach 1. Though the scale included ratings up through F12, Fujita only intended that F0 through F5 ever be used operationally.
The main challenge came in determining what wind speed a given tornado had based only on the damage it left behind. When Fujita first wrote the scale, very little was known about the level of wind required to cause a particular amount of damage to a building, so the connection between a particular range of wind speeds and associated damage was based mainly on educated guesses. Additionally, the scale did not take into account differences in the quality of construction of various buildings (what looked like F3 damage could have actually been an F1 tornado hitting a poorly-built house), and had no way to evaluate the intensity of tornadoes that failed to hit any structures.
The Enhanced Fujita Scale was the result of the “Fujita Scale Enhancement Project”, conducted between 2000 and 2004 at the Wind Science and Engineering Research Center at Texas Tech University. Its goal was to address the shortcomings of the Fujita Scale and devise an “enhanced” version that would more accurately assess wind speed based on the damage documented in NWS field surveys. In addition to revising the wind thresholds for the various EF0 to EF5 categories, the Enhanced Fujita scale also added new guidelines for different types (and qualities) of structures, including vegetation. The new scale was unveiled by the NWS at the 2006 AMS Annual Meeting in Atlanta, and began operational use in February of 2007.
As we noted above, Greensburg received the dubious distinction of being hit by the first confirmed EF5 tornado. Many cable outlets, including the Weather Channel and the Discovery Channel, commemorated the one-year anniversary of the tragedy by reporting live from Greensburg and airing special documentaries about the storm that devastated the town. But how is Greensburg doing now?
Now, one year later, the town is still in the process of rebuilding. In the wake of the tornado, the Greensburg City Council passed a resolution which requires all buildings to be rebuilt to meet the strictest level of environmental standards as certified by the Leadership in Energy and Environmental Design Green Building Rating System, making Greensburg the first town in the nation to do so. Residents remain optimistic—on their website, the citizens of Greensburg state that “We strongly believe that we will be back, better than ever, and will be a model for rural America."
Story is ©
Nate Snook, 2008
