NOAA’s Misleading Tornado Graph

By Paul Homewood

http://www.ncdc.noaa.gov/sotc/tornadoes/201513

Time for my annual moan!

The graph above comes from NOAA’s Annual Tornado Report for 2015. (They also have monthly reports which show similar charts).

Looking at the report, you would understandably believe that tornadoes have been getting steadily more common over the years, and that it presumably must be something to do with global warming.

But as we already know, it is nothing of the sort. The increase in tornado numbers is simply a function of changing reporting practices and technology. NOAA themselves explain all this as follows:

Today, nearly all of the United States is reasonably well populated, or at least covered by NOAA’s Doppler weather radars. Even if a tornado is not actually observed, modern damage assessments by National Weather Service personnel can discern if a tornado caused the damage, and if so, how strong the tornado may have been. This disparity between tornado records of the past and current records contributes a great deal of uncertainty regarding questions about the long-term behavior or patterns of tornado occurrence. Improved tornado observation practices have led to an increase in the number of reported weaker tornadoes, and in recent years EF-0 tornadoes have become more prevelant in the total number of reported tornadoes. In addition, even today many smaller tornadoes still may go undocumented in places with low populations or inconsistent communication facilities.

With increased National Doppler radar coverage, increasing population, and greater attention to tornado reporting, there has been an increase in the number of tornado reports over the past several decades. This can create a misleading appearance of an increasing trend in tornado frequency. To better understand the variability and trend in tornado frequency in the United States, the total number of EF-1 and stronger, as well as strong to violent tornadoes (EF-3 to EF-5 category on the Enhanced Fujita scale) can be analyzed. These tornadoes would have likely been reported even during the decades before Doppler radar use became widespread and practices resulted in increasing tornado reports. The bar charts below indicate there has been little trend in the frequency of the stronger tornadoes over the past 55 years.

http://www.ncdc.noaa.gov/climate-information/extreme-events/us-tornado-climatology/trends

The problem is that explanation is tucked away in the Historical Records and Trends section, which the vast majority of people don’t know about, and would not know where to find if they did.

Indeed, we also know that in reality tornadoes have been getting less common, particularly the stronger ones.

The question this leaves is why do NOAA persist in highlighting a graph, at the very top of the Annual Report, which they know to be totally and grossly misleading?

If you want evidence that NOAA has become overtly politicised, then look no further.