Here’s how a tornado’s strength is measured

NASHVILLE, Tenn. (WSMV) - The strength of a tornado is based on what is called the Enhanced Fujita Scale, a years-old way of classifying how intense a tornado was based on damage and wind speeds, among many other factors.

The Fujita (F) Scale was originally developed in 1971 by Dr. Tetsuya Theodore Fujita to estimate tornado wind speeds based on damage left behind by a tornado. In 2007, the well-known tornado measuring system was tweaked with some improvements by a forum of nationally renowned meteorologists and wind engineers and became what we now know as the Enhanced Fujita (EF) Scale.

According to the National Weather Service, the EF Scale takes into account more variables than the original F Scale did when assigning a wind speed rating to a tornado. The EF Scale incorporates 28 damage indicators (DIs) such as building type, structures, and trees. For each damage indicator, there are 8 degrees of damage (DOD) ranging from the beginning of visible damage to complete destruction of the damage indicator. The original F Scale did not take these details into account.

The Storm Prediction Center has a brief description of the Enhanced Fujita Scale:

EF-0: Light damage. Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over.

EF-1: Moderate damage. Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken.

EF-2: Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off the ground.

EF-3: Severe damage. Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance.

EF-4: Devastating damage. Well-constructed houses and whole frame houses completely leveled; cars thrown and small missiles generated.

EF-5: Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 109 yards; high-rise buildings have significant structural deformation; incredible phenomena will occur.

After a major storm that produces a tornado, the National Weather Service sends out a team of meteorologists from the local forecast office to survey and assess the damage in the impacted areas. After gathering photos and documenting their finding, they release an official report to the public. This could take a matter of hours, but depending on how extensive the damage was, it could take several days. They release their data based on the measurements from the Enhanced Fujita scale.