Preliminary Tornado Report for 2012: a low year

Guest post by Paul Homewood

Although tornado numbers still need to be confirmed for November/December, NOAA have issued their report for 2012.

It has been abundantly clear for several months that the year would be one of the quietest on record. I was therefore more than a little surprised to see this graph NOAA put right at the top of their page.

http://www.ncdc.noaa.gov/sotc/tornadoes/2012/13

Although they rather grudgingly comment that “tornado activity during 2012 was below average”, the impression is clearly given that tornado numbers in recent years, and even 2012, are much higher than in earlier decades. And, of course, many readers will simply look at the graph, read the first paragraph, and walk away with that very impression.

This impression would be most definitely a wrong one. Let me explain.

The above graph is based on total number of tornadoes reported, everything from the weak EF-0 ones right up to killer EF-5’s. As NOAA themselves acknowledge elsewhere, on their excellent “Tornado Climatology” website:-

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 NWS 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 the number of EF-0 and EF-1 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 true variability and trend in tornado frequency in the U.S., the total number of strong to violent tornadoes (EF3 to EF5 category on the Enhanced Fujita scale) can be analyzed. These are the tornadoes that would have likely been reported even during the decades before Doppler radar use became widespread and practices resulted in increasing tornado reports. The bar chart below indicates there has been little trend in the frequency of the strongest tornadoes over the past 55 years.

[For instance, Doppler radar was phased in from 1992-97]

Their graph only runs to 2011, but the preliminary total of EF-3+ for 2012 is 33, as illustrated in my graph below.

Out of the 43 years since 1970, there have been 15 with less EF-3+ tornadoes, so it is not exactly an uncommon occurrence. In terms of total tornadoes, the Storm Prediction Centre project that 2012 will be the quietest year since at least 2005 .

My own analysis suggests a total of about 920 total tornadoes, including 350 EF-1 or stronger. If the latter figure is right, this would leave 2012 as the 3rd quietest year for EF1+ tornadoes since 1970. Only 1987, with 316, and 2002, with 311, had fewer.

The November and December numbers will not be confirmed till March, when I will do the usual full analysis, including a look at whether early season tornadoes are on the increase.

After Thought

I cannot finish without revisiting my opening comments.

For NOAA to present the graph that they have at the very start of their report is, in my opinion, not only grossly misleading, but deliberately so.

They cannot claim ignorance, as they themselves already have already admitted that such comparisons are invalid.

Given the misleading data recently issued by other bodies, such as the UK Met Office, it is hard to avoid the conclusion that NOAA deliberately took the decision to publish this particular graph, rather than the more relevant strong tornadoes version, in order to promote their message that “extreme weather” is increasing.

For the second time this week, I am forced to ask the question –  “ Is this really what “science” has come down to?”

References

1) Analysis of 2012 data is from NOAA’s Storm Events Database

http://www.ncdc.noaa.gov/stormeven

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Addendum by Anthony:

January 9th, 2013 marked a milestone in U.S. tornado history. That day marked the longest stretch of days without a tornado death. It will go down in recorded history as the longest streak with no tornado deaths: 197 days and as of this writing, 201 days and is still climbing.