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"Dixie Alley" is a colloquial term sometimes used for areas of the southern United States which are particularly vulnerable to strong to violent tornadoes. [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 by National Severe Storms Forecast Center (NSSFC) Director Allen Pearson after witnessing a tornado outbreak which included more than 9 long-track, violent tornadoes that killed 121 on February 21–22, 1971. [2] The specific characteristics of the Southeast led to VORTEX-SE, a field project studying tornadogenesis, diagnosis and forecasting, in addition to social science implications, and examines both supercellular tornadoes and those resulting from quasi-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 lower Mississippi Valley. [7] It stretches from eastern Texas and Arkansas across Louisiana, Mississippi, Tennessee, Alabama, Georgia, and mid to western Kentucky to upstate South Carolina and western North Carolina; the area reaches as far north as southeast Missouri. [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 (excluding Texas). 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 of manufactured homes in the US, where 63% of the overall tornado-related fatalities occur. [10] According to the National Climatic Data Center (NCDC), for the period January 1, 1950 – October 31, 2006, Alabama and Kansas received the largest amount of F5 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 hilly topography 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 often high precipitation supercells due to an increase of moisture from proximity to the nearby Gulf 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 storm spotters and chasers, law enforcement, and the public. [10] [13] Increases of warmth and instability in conjunction with strong wind 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 focused tornado 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 the 2008 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 traditional Tornado Alley, especially areas from north-central Texas toward the Houston, Texas area, and relatively-higher tornado frequency and impacts in parts of the Mid-South, especially eastern Arkansas, the greater Memphis, Tennessee area and northern Mississippi – all areas near the heart of Dixie Alley (see especially Figure 4). [16]
Variations in climate patterns and teleconnections, such as the El 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 numerous tornado outbreaks throughout history, including very intense outbreaks and those of very large spatial and temporal extent. Notorious outbreaks affecting the region include: the Great Natchez Tornado, the 1884 Enigma tornado outbreak, the April 1924 tornado outbreak, the 1932 Deep South tornado outbreak, the 1936 Tupelo–Gainesville tornado outbreak, the April 1957 Southeastern tornado outbreak, the 1984 Carolinas tornado outbreak, and the November 1992 tornado outbreak. The 1974 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 the tornado 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 the 2011 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] The Easter 2020 Tornado Outbreak also happened in Dixie Alley. It spawned over 100 tornadoes and has a spot in the top most tornadoes in 24 hours in an outbreak.
A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward the surface of the Earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 180 kilometers per hour, are about 80 meters across, and travel several kilometers before dissipating. The most extreme tornadoes can attain wind speeds of more than 480 kilometers per hour (300 mph), are more than 3 kilometers (2 mi) in diameter, and stay on the ground for more than 100 km (62 mi).
A supercell is a thunderstorm characterized by the presence of a mesocyclone, a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms, supercells are the overall least common and have the potential to be the most severe. Supercells are often isolated from other thunderstorms, and can dominate the local weather up to 32 kilometres (20 mi) away. They tend to last 2–4 hours.
A mesocyclone is a meso-gamma mesoscale region of rotation (vortex), typically around 2 to 6 mi in diameter, most often noticed on radar within thunderstorms. In the northern hemisphere it is usually located in the right rear flank of a supercell, or often on the eastern, or leading, flank of a high-precipitation variety of supercell. The area overlaid by a mesocyclone’s circulation may be several miles (km) wide, but substantially larger than any tornado that may develop within it, and it is within mesocyclones that intense tornadoes form.
The 1974 Super Outbreak was the second-largest tornado outbreak on record for a single 24-hour period, just behind the 2011 Super Outbreak. It was also the most violent tornado outbreak ever recorded, with 30 violent tornadoes confirmed. From April 3–4, 1974, there were 148 tornadoes confirmed in 13 U.S. states and the Canadian province of Ontario. In the United States, tornadoes struck Illinois, Indiana, Michigan, Ohio, Kentucky, Tennessee, Alabama, Mississippi, Georgia, North Carolina, Virginia, West Virginia, and New York. The outbreak caused roughly $843 million USD in damage, with more than $600 million occurring in the United States. The outbreak extensively damaged approximately 900 sq mi (2,331 km2) along a total combined path length of 2,600 mi (4,184 km). At one point, as many as 15 separate tornadoes were occurring simultaneously.
From May 2 to 8, 1999, a large tornado outbreak took place across much of the Central and parts of the Eastern United States, as well as southern Canada. During this week-long event, 152 tornadoes touched down in these areas. The most dramatic events unfolded during the afternoon of May 3 through the early morning hours of May 4 when more than half of these storms occurred. Oklahoma experienced its largest tornado outbreak on record, with 70 confirmed. The most notable of these was the F5 Bridge Creek–Moore tornado which devastated Oklahoma City and suburban communities. The tornado killed 36 people and injured 583 others; losses amounted to $1 billion, making it the first billion-dollar tornado in history. Overall, 50 people lost their lives during the outbreak and damage amounted to $1.4 billion. For these reasons, the outbreak is known in Oklahoma as the May 3rd outbreak or the Oklahoma tornado outbreak of 1999.
A waterspout is a rotating column of air that occurs over a body of water, usually appearing as a funnel-shaped cloud in contact with the water and a cumuliform cloud. There are two types of waterspout, each formed by distinct mechanisms. The most common type is a weak vortex known as a "fair weather" or "non-tornadic" waterspout. The other less common type is simply a classic tornado occurring over water rather than land, known as a "tornadic", "supercellular", or "mesocyclonic" waterspout, and accurately a "tornado over water". A fair weather waterspout has a five-part life cycle: formation of a dark spot on the water surface; spiral pattern on the water surface; formation of a spray ring; development of a visible condensation funnel; and ultimately, decay. Most waterspouts do not suck up water.
A wall cloud is a large, localized, persistent, and often abrupt lowering of cloud that develops beneath the surrounding base of a cumulonimbus cloud and from which tornadoes sometimes form. It is typically beneath the rain-free base (RFB) portion of a thunderstorm, and indicates the area of the strongest updraft within a storm. Rotating wall clouds are an indication of a mesocyclone in a thunderstorm; most strong tornadoes form from these. Many wall clouds do rotate; however, some do not.
Tornado Alley is a loosely defined location of the central United States and Canada where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to study severe weather in areas of Texas, Louisiana, Oklahoma, Kansas, South Dakota, Iowa, Nebraska, and New York. Tornado climatologists distinguish peaks in activity in certain areas and storm chasers have long recognized the Great Plains tornado belt.
A funnel cloud is a funnel-shaped cloud of condensed water droplets, associated with a rotating column of wind and extending from the base of a cloud but not reaching the ground or a water surface. A funnel cloud is usually visible as a cone-shaped or needle like protuberance from the main cloud base. Funnel clouds form most frequently in association with supercell thunderstorms, and are often, but not always, a visual precursor to tornadoes. Funnel clouds are visual phenomena, but these are not the vortex of wind itself.
Tornadogenesis is the process by which a tornado forms. There are many types of tornadoes and these vary in methods of formation. Despite ongoing scientific study and high-profile research projects such as VORTEX, tornadogenesis is a volatile process and the intricacies of many of the mechanisms of tornado formation are still poorly understood.
Tornadoes have been recorded on all continents except Antarctica. They are most common in the middle latitudes where conditions are often favorable for convective storm development. The United States has the most tornadoes of any country, as well as the strongest and most violent tornadoes. A large portion of these tornadoes form in an area of the central United States popularly known as Tornado Alley. Canada experiences the second most tornadoes. Ontario and the prairie provinces see the highest frequency. Other areas of the world that have frequent tornadoes include significant portions of Europe, South Africa, Philippines, Bangladesh, parts of Argentina, Uruguay, and southern and southeastern Brazil, northern Mexico, eastern and western Australia, New Zealand, and far eastern Asia.
Tornadoes are more common in the United States than in any other country or state. The United States receives more than 1,200 tornadoes annually—four times the amount seen in Europe. Violent tornadoes—those rated EF4 or EF5 on the Enhanced Fujita Scale—occur more often in the United States than in any other country.
The Verification of the Origins of Rotation in Tornadoes Experiment are field experiments that study tornadoes. VORTEX1 was the first time scientists completely researched the entire evolution of a tornado with an array of instrumentation, enabling a greater understanding of the processes involved with tornadogenesis. A violent tornado near Union City, Oklahoma was documented in its entirety by chasers of the Tornado Intercept Project (TIP) in 1973. Their visual observations led to advancement in understanding of tornado structure and life cycles.
This page documents the tornadoes and tornado outbreaks of 2011. Extremely destructive tornadoes form most frequently in the United States, Bangladesh, Brazil and Eastern India, but they can occur almost anywhere under the right conditions. Tornadoes also appear regularly in neighboring southern Canada during the Northern Hemisphere's summer season, and somewhat regularly in Europe, Asia, and Australia.
From April 14–16, 2011, a tornado outbreak, among the largest recorded tornado outbreaks in U.S. history, produced 178 confirmed tornadoes across 16 states, resulting in severe destruction on all three days of the outbreak. A total of 38 people were killed from tornadoes and an additional five people were killed as a result of straight-line winds associated with the storm system. The outbreak of severe weather and tornadoes led to 43 deaths in the Southern United States. This was the largest number of fatalities in an outbreak in the United States since the 2008 Super Tuesday tornado outbreak. It is locally referred to as the "Forgotten Outbreak" in Alabama as it was vastly overshadowed by the 2011 Super Outbreak less than two weeks later.
The 2011 Super Outbreak was the largest, costliest, and one of the deadliest tornado outbreaks ever recorded, taking place in the Southern, Midwestern, and Northeastern United States from April 25 to 28, 2011, leaving catastrophic destruction in its wake. Over 175 tornadoes struck Alabama, Mississippi, and Tennessee, which were the most severely damaged states. Other destructive tornadoes occurred in Arkansas, Georgia, Kentucky, Louisiana, New York, and Virginia, with storms also affecting other states in the Southern and Eastern United States. In total, 360 tornadoes were confirmed by NOAA's National Weather Service (NWS) and Government of Canada's Environment Canada in 21 states from Texas to New York to southern Canada. Widespread and destructive tornadoes occurred on each day of the outbreak. April 27 was the most active day, with a record 216 tornadoes touching down that day from midnight to midnight CDT. Four of the tornadoes were rated EF5, which is the highest ranking on the Enhanced Fujita scale; typically these tornadoes are recorded no more than once a year.
From May 21 to May 26, 2011, one of the largest tornado outbreaks on record affected the Midwestern and Southern regions of the United States. A six-day tornado outbreak sequence, most of the tornadoes developed in a corridor from Lake Superior southwest to central Texas, while isolated tornadoes occurred in other areas. An especially destructive EF5 tornado destroyed one-third of Joplin, Missouri, resulting in 158 deaths and over 1,000 injuries. The Joplin tornado was the deadliest in the United States since April 9, 1947, when an intense tornado killed 181 in the Woodward, Oklahoma, area. Tornado-related deaths also occurred in Arkansas, Kansas, Minnesota, and Oklahoma. Overall, the tornado outbreak resulted in 186 deaths, 8 of those non-tornadic, making it second only to the 2011 Super Outbreak as the deadliest since 1974. It was the second costliest tornado outbreak in United States history behind that same April 2011 outbreak, with insured damage estimated at $4–7 billion.
The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.
The 2011 Smithville, Mississippi tornado was an extremely violent EF5 wedge tornado that devastated areas of rural Mississippi and Alabama, including the town of Smithville, Mississippi during the afternoon of April 27, 2011, resulting in catastrophic damage and numerous fatalities. This tornado was a part of the 2011 Super Outbreak, the largest tornado outbreak in United States history. The tornado reached an estimated maximum width of 3⁄4 of a mile with estimated wind speeds up to 205 mph (330 km/h).
The 2010–11 North American winter was influenced by an ongoing La Niña, seeing winter storms and very cold temperatures affect a large portion of the Continental United States, even as far south as the Texas Panhandle. Notable events included a major blizzard that struck the Northeastern United States in late December with up to 2 feet (24 in) of snowfall and a significant tornado outbreak on New Year's Eve in the Southern United States. By far the most notable event was a historic blizzard that impacted areas from Oklahoma to Michigan in early February. The blizzard broke numerous snowfall records, and was one of the few winter storms to rank as a Category 5 on the Regional Snowfall Index. In addition, Oklahoma set a statewide low temperature record in February.