The United States has the largest number of tornadoes of any country in the world. More than 1000 tornadoes are reported each year on average across the country. The public has the notion that tornadoes cause more fatalities than most other weather events. However, during a recent 30 year span (1971-2000), more people have drowned in floods (an average of 127 per year) and killed by lightning (an annual average of 73) than by tornadoes (a yearly average of 69 fatalities).
Tornado statistics have been compiled in various states for more than a century. However, statistics from the entire country are only reliable since 1950, when the predecessor to the National Weather Service's Storm Prediction Center (SPC) at Norman, OK began research into tornadoes. This center routinely posts an updated SPC Monthly Tornado Statistics list of the total number of tornadoes and tornado fatalities for the last several years. Identifying the number of tornadoes is not an easy task. Preliminary statistics (PREL) are based upon numbers that have been obtained from the Local Storm Reports submitted by the National Weather Service Offices within hours after a tornado has been reported. A list of final or "actual" statistics (ACT) concerning the number of reported tornadoes is prepared following the checking and verification of more detailed information. The final numbers may vary considerably from the preliminary list, and typically are lower since some multiple preliminary reports of the same tornado are eliminated in the final count. A killer tornado is, by definition, a tornado that has caused at least one fatality.
Inspection of the most recent list (valid through last Thursday, 12 November 2009) reveals that during the first eleven months of 2009, roughly 1250 tornadoes have been reported across the United States. For the year to date, 22 people have lost their lives in 10 killer tornadoes. With one month remaining, the preliminary number of tornadoes and the number of fatalities in 2009 are both below the average numbers reported during the last three years.
A record number of tornadoes (1819) were reported in 2004, surpassing the 1424 tornadoes in 1998. In contrast, only 656 tornadoes were reported in 1987. For comparison, last year (2008) had 1691 tornadoes. After years of relatively few tornado-related deaths, 1998 also saw the largest number of fatalities (130) since 1974 when 366 people lost their lives during a year that had a memorable tornado outbreak on 3-4 April. A relatively large number of fatalities (95) also occurred during the following year (1999), with roughly half (48 fatalities) occurring as 6 killer tornadoes moved through central Oklahoma near Oklahoma City on the evening of 3 May 1999. Four of these tornadoes were rated F-4 on the Fujita Scale, and one was an incredible F-5 tornado.
The number of fatalities decreased in 2000 and 2001 (40 fatalities each year), before increasing in 2002 (55 fatalities), then decreasing slightly in 2003 (54 fatalities) and by even more in 2004 (36 fatalities). Numbers increased slightly in 2005 (38 fatalities), then much more in 2006 (67 fatalities), 2007 (81 fatalities) and 2008 (126 deaths).
The National Climatic Data Center has provided a climatology of U.S. tornadoes, to include maps that show the number of tornadoes by state and other statistics. The Storm Prediction Center has an interactive website entitled Online Severe Weather Climate that includes the number of tornadoes along with other severe weather statistics within the National Weather Service's radar coverage areas during the last three decades.
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Prepared by Edward J. Hopkins, Ph.D., email
hopkins@meteor.wisc.edu
© Copyright, 2009, The American Meteorological Society.