Tornado observed by the VORTEX-99 team on May 3, 1999, in central Oklahoma.
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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.
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