The highest frequency of killer tornadoes occurs in Dixie Alley, a region that stretches from north Texas to Tennessee and includes parts of Arkansas, Mississippi, and Alabama. On average, about half of all killer tornadoes in the United States happen in this area.

One of the reasons Dixie Alley sees so many killer tornadoes at night is because the air in the area is often humid and unstable. This makes it more likely for severe thunderstorms to develop, and when these storms do develop, they can quickly produce tornadoes.

Another factor that contributes to the high frequency of killer tornadoes in Dixie Alley is the area's geography. Dixie Alley is located at the intersection of several different air masses, and these air masses can interact in a way that creates the perfect conditions for tornadoes.

Finally, Dixie Alley is also located near the jet stream, a narrow band of high-altitude winds that can influence the formation of tornadoes. When the jet stream is positioned in a certain way, it can create the ideal conditions for severe thunderstorms to develop.

All of these factors combined make Dixie Alley a hotbed for killer tornadoes. At night, when the air is humid and unstable, and the jet stream is in the right position, Dixie Alley is at its most vulnerable to these deadly storms.