The significant tornado in New Castle/Moore, Oklahoma this week has spurred a lot of discussion about violent tornadoes and their impact to the central United States. Some people, including Bill Nye, have noted stronger tornadoes are just a fact of life which will need to be dealt with as our environment “changes”.
History does not agree.
Looking back at the most violent tornadoes in US history classified as EF-5 (formerly F-5 tornadoes on the Fujita scale), there have been some pretty busy decades. The problem, in terms of short-term memory, is that they did not occur very frequently in more recent times.
This graphic shows the paths of EF-5 tornadoes over the last 60 plus years. Before looking at the data by year, it’s interesting to note the seasonal occurrences of these destructive tornadoes. Most of the EF-5 tornadoes in Oklahoma almost exclusively occurred in the month of May:
These strongest tornadoes cluster in the southeast earlier in the season, and tend to shift westward as the season progresses. Why? Generally speaking, conditions that drive the formation of these storms are move favorable in the south during the early spring. As the upper level dynamics and low-level moisture fields shift toward the Great Plains in the spring, the strong tornadoes follow along.
Also, notice the attached table showing the number of observed EF-5 tornadoes, by decade, since 1950. The numbers are striking, we had 10 or more EF-5 tornadoes in each decade from 1950-1979, only three in the 80’s, only 2 from 2000-2009, and now 6 entering 2012 (the NWS/SPC database is only complete through 2011 at the time of this post).
Coming into the 2012 season, we have already observed 6 EF-5 rated tornadoes in the current decade.
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Here’s a more detailed table, courtesy of the Storm Prediction Center.
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