Tornado Scales



Tornado observed by the VORTEX-99 team on May 3, 1999, in central Oklahoma.
Click on image for full size (152K JPEG)
Figure courtesy of NOAA
Suppose someone put two boxes in front of you, one small and one large. The boxes are sealed tightly and you can't see what's in them. You wouldn't know which box would be heavier because you don't know what's in them. You might think the large box would be heavy and the small box light. But what if the large box was empty and the small box contained rocks. Then that would be a surprise!

Tornadoes are a little bit like those boxes. You can't tell how strong a tornado is by looking at its size! Big tornadoes might be strong or weak.

So scientists group tornadoes based on the damage they cause. That is, they group them after they are gone, not before. This scale is called the Enhanced Fujita Scale and it has been used since 2007.

For more information- The Enhanced Fujita Scale - NOAA's Storm Prediction Center

Earth's Weather

Tornadoes Section

Tornado Scales



Tornado observed by the VORTEX-99 team on May 3, 1999, in central Oklahoma. Note the tube-like condensation funnel, attached to the rotating cloud base, surrounded by a translucent dust cloud.
Click on image for full size (152K JPEG)
Figure courtesy of NOAA
Before 1971, there was no way for scientists to rank tornadoes by their strength. How big the tornado looked had no bearing on how strong it actually was. In 1971, Professor Fujita came up with a system to rank tornadoes according to how much damage they cause. This was called the Fujita Scale.

As of February 1, 2007, a new scale for rating the strength of tornadoes is being used. It is called the Enhanced Fujita Scale.

The Enhanced Fujita Scale or EF Scale has six categories from zero to five, with EF5 being the highest degree of damage. The Scale was used the first time as three separate tornadoes took place in central Florida early on February 2, 2007. These tornadoes destroyed many houses and businesses and killed at least 21 people. And these tornadoes were only rated EF3 tornadoes!

Scientists have to figure out how strong a tornado was after it hits. Because the scale is based on the damage caused by it, they can't predict how strong a tornado would be before it happens.

For more information- The Enhanced Fujita Scale - NOAA's Storm Prediction Center

Earth's Weather

Tornadoes Section

Tornado Scales



Tornado observed by the VORTEX-99 team on May 3, 1999, in central Oklahoma. Note the tube-like condensation funnel, attached to the rotating cloud base, surrounded by a translucent dust cloud.
Click on image for full size (152K JPEG)
Figure courtesy of NOAA
Before 1971, there was no way to categorize tornadoes by their strength. Without a standard system to rank tornadoes, there was no way to keep an accurate storm record; everybody had their own idea of how strong the storm was. In 1971, T. Theodore Fujita, a professor at the University of Chicago, came up with a system that equated wind speed with tornado damage. This original Fujita tornado scale had six categories from F0 to F5.

A new scale for rating the strength of tornadoes became operational on February 1, 2007 and it is called the Enhanced Fujita Scale.

The Enhanced Fujita Scale or EF Scale has six categories from zero to five, with EF5 being the highest degree of damage. The Scale was used the first time as three separate tornadoes took place in central Florida early on February 2, 2007. These tornadoes destroyed many houses and businesses and killed at least 21 people. And these tornadoes were only rated EF3 tornadoes.

The first time the EF5 measurement was recorded was in the Greensburg, KS tornado that occurred on May 4, 2007. The tornado was estimated to be 1.7 miles in width and traveled for over 22 miles. Its winds reached 205 mph. The city of Greensburg was virtually destroyed and 12 people lost their lives that day. Tornado sirens were sounded in Greensburg twenty minutes before the tornado hit, certainly saving countless lives. Still, much better tornado forecasting is needed to give even earlier warnings.

Scientists have to figure out how strong a tornado was after it is over. Because the scale is based on the damage caused by it, they can't predict how strong a tornado would be before it strikes.

For more information- The Enhanced Fujita Scale - NOAA's Storm Prediction Center

Earth's Weather

Tornadoes Section


Last modified May 8, 2008 by Jennifer Bergman.
The source of this material is Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporation for Atmospheric Research (UCAR). © The Regents of the University of Michigan. Windows to the Universe® is a registered trademark of UCAR. All Rights Reserved. Site policies and disclaimer