On the main blog, there's a chart showing the number of strong to violent EF-3, EF-4 and EF-5 tornadoes from 1950 to 2011. According to that chart's caption, "...There is not a decades-long increasing trend in the numbers of these most dangerous of tornadoes..."
Personally, I see a problem with the chart. Mainly, the F scale was introduced in 1971 by Tetsuya Fujita of the University of Chicago.
"...In the United States, tornadoes from 1973 onward were rated soon after occurrence whereas the scale was applied retroactively to tornado reports from 1950 through 1972 for the National Oceanic and Atmospheric Administration (NOAA) National Tornado Database..."
The Fujita scale is effectively a damage scale, and the wind speeds associated with the damage listed aren't rigorously verified.
So, the F-rating of storms prior to '73 were determined long after the storm, and probably long after the damage was repaired/removed. How accurate were the written reports and photographs?
Second, is the Enhanced scale (EF-ratings). The Fujita scale was superseded in 2007 by the Enhanced Fujita Scale in the United States (and is biased to US construction practices).
Once again, in order to match like-to-like, the historic records SHOULD be re-examined to re-rate them to the enhanced scale. Because as the US changed since 1950, so did their construction practices and construction codes.
A building constructed in the 1950's, probably wood framed, may be no match for those built today (treated woods, braces, trusses, etc).
So to say this chart accurately reflects the number of EF-3, EF-4 and EF-5 tornadoes back to 1950 is, IMHO, just a LITTLE off.
Updated: 02:07 AM GMT del 05 Giugno 2011
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