Tornadoes shift to Southeast, where they tend to be deadlier because of timing (night), geography and population density

Northern Illinois University map; click on it to enlarge

"Tuesday night’s deadly tornado that struck the New Orleans area is the ideal example of what experts say is the 21st century problem with twisters: Killer tornadoes have shifted a bit out of the vast emptiness of the Great Plains, more into the Southeast where there are more people to hit, poorer populations and more trees to obscure twisters from view," Seth Borenstein reports for The Associated Press. "Since 2000, nearly 89% of the 1,653 Americans killed by tornadoes — not counting this week’s victims — lived east of the Dakotas, Nebraska, Kansas, Oklahoma and Texas, according to an Associated Press analysis of National Oceanic and Atmospheric Administration data."

These tornadoes aren't necessarily more powerful than the ones that hit the Great Plains; they're just hitting more densely populated areas. Twisters in Tornado Alley, in contrast, can go for miles without hitting much, Borenstein reports.

Climate change plays a major part in why tornado frequency is shifting east to "tornado fatality alley in the Mid-South, according to a 2018 study by Victor Genseni, a Northern Illinois University meteorology professor who specializes in severe storms, and Harold Brooks, a senior scientist at NOAA’s National Severe Storms Laboratory. "What’s likely happening is that the West is getting drier because of human-caused climate change, which makes it harder for the air to become moist and unstable, which is crucial for tornado formation, they said," Borenstein reports. "The Southeast is getting warmer air, which holds more water vapor, which creates that important instability."

Southeastern tornadoes also tend to be deadlier because they're more prone to happen at night. "About three-quarters of the tornadoes that hit Oklahoma and other Great Plains states occur between 5 and 9 p.m. so people know when to expect them and its more daylight, Brooks said. But in the Southeast they can hit any time, which means more often at night than in Oklahoma, making them more dangerous," Borenstein reports. "Another reason they happen more at night in the Southeast is because they happen more in the springtime and there are just fewer daylight hours, Gensini said. Spring storms are juicier and stronger than summer ones so they don’t need the sun’s daytime heat to add that extra kick of energy to spur tornadoes, he said."

The Southeast also has more trees, hills, and buildings that can block people's sight lines and keep them from seeing a twister coming; that can make them less likely to heed a tornado warning, Borenstein reports. But, "The one advantage tornadoes in the Southeast have is that they are easier for meteorologists to forecast the conditions ripe for bad outbreaks much earlier."