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"Dixie Alley" is a colloquial term sometimes used for areas of thesouthern United States which are particularly vulnerable tostrong to violenttornadoes.[1] Some argue this is distinct from the better known "Tornado Alley" and that it has a high frequency of strong, long-track tornadoes that move at higher speeds.[citation needed] The term was coined byNational Severe Storms Forecast Center (NSSFC) DirectorAllen Pearson after witnessing a tornado outbreak which included more than 9 long-track, violent tornadoes that killed 121 onFebruary 21–22, 1971.[2] The specific characteristics of the Southeast led toVORTEX-SE, a field project studyingtornadogenesis, diagnosis and forecasting, in addition to social science implications, and examines bothsupercellular tornadoes and those resulting fromquasi-linear convective system (QLCS) thunderstorm structures.[3][4] This was followed a few years later by another major field project, PERiLS, focusing on QLCS tornadoes.[5][6]
Dixie Alley includes much of the area of the lowerMississippi Valley.[7] It stretches from easternTexas andArkansas acrossLouisiana,Mississippi,Tennessee,Alabama,Georgia, and mid to westernKentucky to upstateSouth Carolina and westernNorth Carolina; the area reaches as far north as southeastMissouri.[8] Another source places all of Arkansas within Dixie Alley.[9]
Although tornadoes are less frequent in these states than they are in the southern Plains[citation needed], the southeastern states have had more tornado-related deaths than any of the Plains states (excludingTexas). This is partly due to the fact that there are relatively high numbers of strong/violent long tracked tornadoes and higher population density of this region, as well as the Southern United States having the highest percentage ofmanufactured homes in the US, where 63% of the overall tornado-related fatalities occur.[10] According to theNational Climatic Data Center (NCDC), for the period January 1, 1950 – October 31, 2006, Alabama andKansas received the largest number ofF5 tornadoes. Complicating matters is that tornadoes are rarely visible in this area, as they are more likely to be rain-wrapped, embedded in shafts of heavy rain, and that the hillytopography and heavily forested landscape makes them difficult to see.[10]
Dixie Alley is part of a region of enhanced tornadic activity extending between the Appalachian and Rocky Mountains,[11] but tornadoes and outbreaks in the Dixie Alley region exhibit some statistically distinguishable characteristics from the more well known Tornado Alley.[12] Tornadic storms in Dixie Alley are most oftenhigh precipitation supercells due to an increase of moisture from proximity to the nearbyGulf of Mexico. The Dixie Alley tornadoes accompanying the HP supercells are often partially or fully wrapped in rain, impairing the visibility of the tornadoes to stormspotters andchasers, law enforcement, and the public.[10][13] Increases of warmth andinstability in conjunction with strongwind shear in the Dixie Alley region impacts the times when tornadoes form. In the traditional Tornado Alley, tornadoes most often form from the mid afternoon to early evening. Dixie Alley's instability can be maintained long after sunset due to being adjacent to the Gulf, increasing the frequency of intense nighttime and early morning tornadoes.[10] There is also a less focusedtornado season which tends to be most active in early spring and late autumn but can continue throughout the winter and into late spring, which can lead to complacency among residents of the region. The region often is subject to tornadoes much earlier than the general national peak from May and June, usually from February to Mid-April,[14] and several notorious outbreaks have struck during the late winter and early spring and also in late fall.[10] The complacency situation was noted after the2008 Super Tuesday tornado outbreak in February 2008 that hit the Dixie Alley killing 57 people, many people indicated that they had underestimated the threat of severe weather on that day since it was well before the peak of tornado season.[10]
A 2018 study found in the U.S. an overall eastward shift of tornado frequency and impacts – toward Dixie Alley.[15] The study found relatively-lower tornado frequency and impacts in parts of the traditionalTornado Alley, especially areas from north-central Texas toward the Houston, Texas area, and relatively-higher tornado frequency and impacts in parts of theMid-South, especially eastern Arkansas, the greaterMemphis, Tennessee area, Western Kentucky, and northern Mississippi – all areas near the heart of Dixie Alley (see especially Figure 4).[16]
Variations inclimate patterns andteleconnections, such as theEl Niño–Southern Oscillation (ENSO) can also have significant impacts on tornadic activity in the region from year to year.Climate change is also expected to affect tornado activity in the region.[17][18]
Dixie Alley has been subject to numeroustornado outbreaks throughout history, including very intense outbreaks and those of very large spatial and temporal extent. Notorious outbreaks affecting the region include: theGreat Natchez Tornado, the1884 Enigma tornado outbreak, theApril 1924 tornado outbreak, the1932 Deep South tornado outbreak, the1936 Tupelo–Gainesville tornado outbreak, theApril 1957 Southeastern tornado outbreak, the1984 Carolinas tornado outbreak, and theNovember 1992 tornado outbreak. The1974 Super Outbreak also hit the area very hard, producing multiple F5 tornadoes in Alabama, and F4 tornadoes in North Georgia and the Appalachian southwest of North Carolina. More recently the region was hit by the 2008 Super Tuesday tornado outbreak followed by thetornado outbreak of April 14–16, 2011, the deadliest since the 2008 outbreak.[10] Two weeks after the April 14–16 event, Dixie Alley was the epicenter of the2011 Super Outbreak, which was the largest tornado outbreak ever recorded, as well as the fourth-deadliest outbreak in United States history, with over 300 people dead.[19] TheEaster 2020 Tornado Outbreak also happened in Dixie Alley. It spawned over 100 tornadoes and has a spot inthe top most tornadoes in 24 hours in an outbreak.
