The images below provide a summary of the tornado climatology of the southeastern U.S. (mouse over each image for a description; click for a larger version). Some of the key aspects of these images are described here:
- The average annual tornado frequency in the southeastern U.S. is highest in Florida; however, most of the tornadoes are weak (F/EF-0 to F/EF-1) and spawned by tropical cyclones. Strong (F/EF-2 to F/EF-3) and violent (F/EF-4 to F/EF-5) tornadoes occur most frequently across Alabama, Mississippi, Arkansas, and Louisiana and are responsible for the vast majority of tornado-related casualties. (Tables 1-4)
- Most tornadoes and tornado-related casualties occur during meteorological spring (March to May), with a peak in April, particularly among strong and violent tornadoes. There is also a secondary peak in tornado frequency in November, as well as a secondary peak in casualties in February. (Table 5, Figures 9-14)
- Tornadoes occur most frequently in the late afternoon and early evening hours; however, many killer tornadoes occur during the overnight hours when tornadoes are difficult to see and people are asleep. (Figures 6-8)
- There has been upward trend in the frequency of weak tornadoes since the middle of the 20th century. This is likely due to improvements in radar technology, communication, storm surveys, and storm spotter training, as well as an expanding population, infrastructure, and spotter network. Conversely, there is no discernable trend in either the frequency of or fatalities associated with strong and violent tornadoes over the same period. (Figures 1-5)
How unusual was 2011? The calendar year 2011 saw a remarkable number of tornadoes across the U.S., particularly across the southeastern region (Figure 15). Official data were recently released by NOAA’s Storm Prediction Center, allowing the events of the past year to be placed in a historical context. The tables at the bottom of this page provide a statistical summary of the tornadoes from 2011 across the southeastern U.S.; some key aspects of these tables are described here:
- There were 492 tornadoes of EF-1 intensity and greater recorded across the southeastern U.S. in 2011. The previous annual record number of tornadoes (since 1954) was set in 2008 with 378. (Table 10)
- 2011 ranked as the deadliest tornado year across the southeastern U.S. with 356 fatalities, eclipsing the previous record of 240 fatalities set back in 1974. (Table 10)
- April 2011 ranked as the most active tornado month on record across six southeastern states, including Alabama, Arkansas, Kentucky, Mississippi, Tennessee, and North Carolina. April 2011 was also the deadliest tornado month on record across Alabama and Georgia. (Tables 8-9)
- Most of the tornadoes and tornado-related fatalities in 2011 occurred as part of the “Super Outbreak” from April 25th to the 28th. On April 27th alone, there were 144 tornadoes of EF-1 intensity and greater and 298 fatalities across the southeastern U.S. Both of these numbers eclipse their previous records, which were set back on April 3 during the infamous 1974 “Super Outbreak”. (Tables 6-7)
- F/EF-5 tornadoes are extremely rare across the southeastern U.S.; from 1954 to 2010, only nine such tornadoes had been recorded across the region, the most recent occurring in 1998. Remarkably, four tornadoes in April 2011 reached EF-5 intensity across the region, killing a total of 123 people. (Table 11)
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