Because they are experts in tornadoes and realize that weak frame structures, like barns, offer very little protection from powerful tornadoes.
Although historically rare, tornadoes with an EF5 or F5 rating cause catastrophic damage to the communities they affect. The NOAA Storm Prediction Center reports that 59 tornadoes have been classified as EF5 or F5, or less than one per year on average.
After its 1971 introduction, this was given the name Fujita Scale, or F Scale. According to the scale, tornadoes ranged in intensity from F0 to F5, with F5 being the most powerful with estimated winds of 261 to 318 mph.
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