In a blow to those that want to link increased severe weather with global warming/climate change, a new record low has been set according to NOAA tornado data. At the same time, it has been 2750 days (7 years, 6 months, 11 days) since the last major Hurricane (Cat 3 or greater) hit the USA on October 24th 2005 when hurricane Wilma made landfall. Each new day is a new record in this major hurricane drought.

Essay by Harold Brooks, NOAA National Severe Storms Laboratory

Graph: Harold Brooks: NOAA

The 12-month period from May 2012 to April 2013 was remarkable for the absence of tornado activity and tornado impacts in the United States.

We can start by looking at the number of EF1 and stronger tornadoes during that period. A final count is available through January 2013 and we have a pretty good estimate of how many occurred in February through April, although final numbers won’t be available until July. Although the 12 month total may change a little bit with the final data, it’s unlikely to change enough to affect the results here.

From May 2012-April 2013, the estimate is that there were 197 tornadoes rated EF1 or stronger. Where does that stack up historically? Well, we have pretty good data back to 1954. During that time, the previous low for (E)F1 and stronger tornadoes in a 12 consecutive calendar month period was 247, from June 1991-May 1992. The next lowest (ignoring the overlapping periods, such as April 2012-March 2013) was 270 from November 1986-October 1987. The lowest non-overlapping 12 month counts on record from 1954-present, with the starting month, are:

197 May 2012 (preliminary)

247 June 1991

270 November 1986

289 December 2001

298 June 2000

This apparent record was set less than two years after the record for most EF1+ tornadoes in a 12-month period was set, with 1050 from June 2010-May 2011. The time series showing the evolution of the number of (E)F1+ tornadoes since 1954 is below. The number of (E)F1+ tornadoes in the 12 months beginning with the time on the x-axis is plotted for every month starting in January 1954 and ending in May 2012, the most recent point.

ef1plus12

The death toll from May 2012-April 2013 was 7. National Weather Service official statistics go back to January 1950, but we can extend that by using the work of Tom Grazulis from the Tornado Project, who has collected tornado fatality information back into the 17th century. The data are reasonably good back to 1875, but it’s still possible that there are some missed fatalities, particularly as we go back farther in time. So, where does 7 fatalities in 12 consecutive calendar months stack up? Again, here are the lowest totals, going back to 1875, for 12 consecutive months, with the starting month. (For overlapping periods, such as April 2012-March 2013 and May 2012-April 2013, only the lowest period is listed.)

5 September 1899

7 May 2012

8 August 1991

12 November 1909

12 May 1940

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Harold Brooks is a research meteorologist with the NOAA National Severe Storms Laboratory in Norman, Oklahoma. ============================================================= Update: Here is an updated chart showing the hurricane drought stretch. Originally done by Dr. Roger Pielke Jr., I’ve updated it since he is taking a blog break. Reference: NOAA/NCDC US Landfalling hurricanes: http://www.aoml.noaa.gov/hrd/tcfaq/E23.html

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