Kentucky: The calendar said December but the warm moist air screamed of springtime. Add an eastbound storm front guided by a La Nina weather pattern into that mismatch and it spawned tornadoes that killed dozens over 5 U.S. states. Tornadoes in December are unusual, but not unheard of. But the ferocity and path length of Friday night’s tornadoes likely put them in a category of their own, meteorologists say. One of the twisters if it is confirmed to have been just one likely broke a nearly 100-year-old record for how long a tornado stayed on the ground in a path of destruction, experts said.
“One word: remarkable; unbelievable would be another,” said Northern Illinois University meteorology professor Victor Gensini. “It was really a late spring type of setup in the middle of December.” Warm weather was a crucial ingredient in this tornado outbreak, but whether climate change is a factor is not quite as clear, meteorologists say. Scientists say figuring out how climate change is affecting the frequency of tornadoes is complicated and their understanding is still evolving. But they do say the atmospheric conditions that give rise to such outbreaks are intensifying in the winter as the planet warms.
Tornado alley is shifting farther east away from the Kansas-Oklahoma area and into states where Friday’s killers hit. Tornadoes are whirling, vertical air columns that form from thunderstorms and stretch to the ground. They travel with ferocious speed and lay waste to everything in their path. Thunderstorms occur when denser, drier cold air is pushed over warmer, humid air, conditions scientists call atmospheric instability. As that happens, an updraft is created when the warm air rises. When winds vary in speed or direction at different altitudes a condition known as wind shear the updraft will start to spin.