This graph shows the annual total of F3/EF3 to F5/EF5 tornadoes in the U.S. since 1950 (data from the Storm Prediction Center)
The EF (Enhanced Fujita) Scale to measure the velocity of winds in a tornado replaced the F (Fujita) Scale in 2007. The number of tornadoes reported since 1950 has increased substantially. There are 3 reasons for this. First, tornadoes in 1950 often went across unpopulated or sparsely populated areas. These areas are not populated and people see them. Second, there is a much better system in place for reporting tornadoes. Finally (since the movie “Twister”), there are now 100 cars (storm-chasers) following every dark cloud. This presents a problem. In the El Reno Tornado of 2013 there were 8 fatalities. All the fatalities were in vehicles and 4 of the fatalites were people “chasing” the tornado.
The reason that the Storm Prediction Center logs a record of EF3 – EF5 tornadoes (strong to violent) is that these storms would have been logged in 1950 and the record of these tornadoes seems very good over a relatively long period of time. Note that there were more EF3 to EF5 tornadoes in the 1960s-1970s than during recent years. We don’t have a shouting out loud answer to why. We still get BIG tornadoes (El Reno OK) and we still get big years (2011), but overall the trend of strong to violent tornadoes has trended down. I personally think this is cyclical and that this calm period will eventually end.
This year has been an overall quiet year for severe weather, but severe weather and tornadoes should pick up with the pattern changing a bit…the first area to see an increase in severe weather will be KS/OK where this has been the quietest year to date ever recorded. They should see their first tornadoes in the coming week.