From NOT A LOT OF PEOPLE KNOW THAT
By Paul Homewood
https://www.spc.noaa.gov/wcm/#data
NOAA’s Storm Prediction Center (SPC) has now published the full data for US tornadoes last year.
First a recap though. Over the years, the ability to observe and measure tornadoes has increased out of all proportion to the situation 50 or so years ago. This is what NOAA said in 2015:
Historical Records and Trends
One of the main difficulties with tornado records is that a tornado, or evidence of a tornado must have been observed. Unlike rainfall or temperature, which may be measured by a fixed instrument, tornadoes are short-lived and very unpredictable. If a tornado occurs in a place with few or no people, it is not likely to be documented. Many significant tornadoes may not make it into the historical record since Tornado Alley was very sparsely populated during the 20th century.
Much early work on tornado climatology in the United States was done by John Park Finley in his book Tornadoes, published in 1887. While some of Finley’s safety guidelines have since been refuted as dangerous practices, the book remains a seminal work in tornado research. The University of Oklahoma created a PDF copy of the book and made it accessible at John Finley’s Tornadoes.
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.
NOAA have now deleted this highly inconvenient document, and instead publish this highly misleading graph every year, implying that tornadoes are more frequent than in the past:
https://www.ncei.noaa.gov/access/monitoring/monthly-report/tornadoes/202213
As the 2015 document shows though, the total of EF-1s and over has changed little over the years. More significantly though the number of strong to violent tornadoes has fallen sharply over time.
Although NOAA stopped updating those two graphs after 2014, the SPC data confirms this trend has continued since:
https://www.spc.noaa.gov/wcm/#data
There have been no EF-5 tornadoes at all for ten years now, since the Moore tornado in 2013; this is the longest period on record.
There is also a strong argument that many EF-1 tornadoes were also missed prior to the roll out of Doppler. As the chart below shows, Ef-1s now account for around 75% of all tornadoes (excl EF-0s), up from 60% or so:
https://www.spc.noaa.gov/wcm/#data
Logically there are only possible explanations for this:
1) Tornadoes are getting weaker on average
2) Many EF-1s went unrecorded in the past, and consequently the total number of tornadoes was understated.
Assuming the second assumption is true, this is what the trend excluding EF-1s looks like:
Neither scenarios fit the NOAA agenda of course, which is why they never mention it now.
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