The United States is known for a number of interesting geological and meteorological oddities, and one of them is the often-discussed Tornado Alley. Tornado Alley is an informal name given to a region of parts of the Southeastern and Midwestern United States that is much more prone to tornado outbreaks than any other part of the world.
The prevalence of tornado activity in the region has led to the rise of storm chasing as a way to better understand the formation and movement of the storms. So, this begs the question: what have storm chasers learned? Why do tornadoes form with such frequency in the region?
A Quick Note
Of course, the formation of tornadoes and their movement patterns are still not well understood. Due to their destructive nature and brief, unpredictable appearance, more data is needed to better understand why some areas are more likely to see tornado activity than others.
What follows is the best guess of numerous meteorologists and storm chasers who have surmised the basic aspects of tornado formation from observation and research. As always, all scientific hypotheses need thorough testing to determine if they are accurate.
The Jet Stream
There are a number of reasons why Tornado Alley is such a magnet for tornado activity, but likely the biggest reason is the jet stream. The jet stream, in this context, refers to the Northern Hemisphere’s polar jet. A jet stream is an air current caused by the uneven heating of the atmosphere by the sun and the Coriolis force of the Earth spinning on its axis.
The fast-flowing jet of polar air that moves from west to east across North America is the culprit for many weather phenomenon in the region, and Tornado Alley is no different. As the jet stream pulls cold, arctic air from the North Pole down across the US, it often encounters fronts of warm, moist air over the Midwest.
Storm Fronts Develop Over Tornado Alley
When the cold, dry air from the jet stream encounters the warm, moist air hanging over the Midwest and Southeast, largely from the Gulf of Mexico, this almost invariable causes storm fronts to form. When these opposing forces of air meet, they can cause cyclogenesis, or the creation of fast-moving storms.
This is due to the tendency of hot air to rise, due to the difference in density between the two. As the warm, moist air rises and meets the cold, dry air, cloud fronts can form that contain immense potential energy. This, in turn, can manifest as large, spinning funnel clouds. Should those clouds shift earthward and touch down, they are referred to as tornadoes.