The United States is one of the locations where a high frequency of tornadoes strike annually in the world. Tornadic activity happens in the United States due to the warm air from the Gulf of Mexico interacting with any frontal system that comes off of the Rocky Mountains. A common conception is that people tend to think that the majority of tornadoes form in the Great Plains of the United States, but there is a second “alley” that is catching the attention of people: Dixie Alley.
Dixie Alley is found in the Southeast part of the United States and includes the following states: Louisiana, Arkansas, Mississippi, Alabama, Georgia, and Tennessee. This region is geographically different and has more diverse landscapes than the Great Plains. The following are a few factors as to why a higher count of tornadoes develop in Dixie Alley: the topography of the land, the type of supercells, in particular, the high precipitation supercell, the two seasonal peaks of tornadoes due to the movement of the jet stream in the spring and fall, when tornadoes strike and the types of homes that people live in all contribute to this pattern.
The land in the Southeast is covered by trees, making it more difficult to see an oncoming tornado. Unlike the Great Plains with miles upon miles of prairie grass for all to see, the trees cut down on one’s ability to see tornadoes approaching from far away. The Southeast is relatively flat, but there are some hills and plateaus that one has to consider when trying to forecast the risk for severe weather. These hills and plateaus can cause a system to become stationary, causing more threats than just tornadoes. There are also major water sources that can fuel a system as well. The Gulf of Mexico feeds a constant supply of warm, moist air to the Southeastern United States, and numerous large bodies of water that can affect the storm.
The most frequent type of supercell is a High Precipitation Supercell. A High Precipitation Supercell is a supercell thunderstorm that has a lot of precipitation associated with it. While rain reduces the chances of a drought, it often obscures the tornado. This creates a rain-wrapped tornado, which cannot be spotted by storm spotters and storm chasers unless they are unfortunate enough to be caught in this area of a supercell. This area where a possible tornado could be is called the bear’s cage, and very few storm chasers want to end up in this area. Radars as well can struggle with picking up a tornado in a high precipitation supercell because of the precipitation obscuring and scattering the signal. Radar technology has improved since its invention, but when the scans only update every five minutes, these scans may not be able to catch every tornado that touches the ground.
By looking at the graph above, the time of day that these tornadoes strike is usually after the sun has gone down, taking away a vital way of spotting tornadoes. This leads to a problem because storm chasers and storm spotters cannot be as effective due to the lack of sunlight illuminating features of the storm that can lead to one to think that there is a chance of tornadoes forming. Plus, at night, people are sleeping and are unable to receive information from multiple sources. As a result, many of the reports of nocturnal tornadoes comes from looking at radar signatures formed by the supercell in question.
The time of year matters as well when a tornado strikes. The Southeast experiences two different annual peaks of tornadic activity because of the movement of the jet stream. As it moves down and up according to the season, it adds another piece of instability into the atmosphere. If the winds are in a different direction at the surface than aloft, then wind shear is present. These two peaks correlate to the Spring and Fall seasons and they occur in April and November. However, these two peaks do not limit the months that tornadoes can occur. They can occur year-round whenever there is a chance of severe weather with the right ingredients.
Finally, where people live makes a major difference as well. There are more trailer parks in portions of the Southeast, and these homes are not made to withstand the high force winds that a tornado can bring. This statement was unfortunately proven correct when an EF-4 tornado struck the town of Beauregard, Alabama on March 3rd, 2019. The people that also live in the Southeast may not have adequate access to a tornado shelter or may not be within hearing distance of the sirens. The sirens are not meant to be heard inside, so if someone is inside a building, they may not know what is coming. There are other ways of receiving the information, such as a NOAA weather radio, but some people may not even have that.
Dixie Alley is a second area in the United States for frequent tornadoes to strike. Although it is getting easier to detect when they are coming, their impacts are well known. From where and when they strike, to how people are warned, these tornadoes can often turn into significant tornadoes, forever changing the lives of those who have survived them.
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Sources Cited: https://www.ncdc.noaa.gov/climate-information/extreme-events/us-tornado-climatology/trends
©2019 Weather Forecaster Shannon Sullivan