Tornadoes are getting wider and touching down longer and they have been coming in bigger clusters, resulting in a dramatic increase in destructive power. US tornadoes have averaged an annual increase of destructive power by 5.5%, since 1994, Dr. James Elsner of Florida State University said in a talk at a meeting of the American Geophysical Union.
While the number of violent EF4 and EF5 tornadoes has remained roughly constant in the U.S. during the time period studied, longer tornado paths is the key reason for the increase in tornado power.
Violent tornadoes increase on days with larger outbreaks, in recent years the increase in the number of days with large clusters of tornadoes suggests a larger threat of damaging tornadoes.
Less than four percent of tornadoes are rated EF3 or worse, on a day with 16 to 31 tornadoes, while days with more than 63 tornadoes, eight percent of the tornadoes are rated EF3 or worse.