Satellite imagery shows Mayfield in Kentucky following Friday’s tornado.
Maxar via Getty Images

WASHINGTON (AP) — The calendar said December but the warm moist air screamed of springtime. It’s easy to see how a La Nina-influenced eastbound storm force and a La Nina weather system can be combined into this mismatch. spawned tornadoes that killed dozensOver five U.S. States

While not common, December tornadoes aren’t unheard-of. However, the ferocity and path length of Friday night’s tornadoesMeteorologists believe they would be in their own category. 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,” Victor Gensini, a Northern Illinois University meteorology professor said. “It was really a late spring type of setup in in the middle of December.”

Although warm weather played a key role in the tornado outbreak, it is unclear if climate change was involved, according to meteorologists.

A U.S. national flag waves among tornado damage after extreme weather hit the region in Bowling Green, Kentucky.
After severe weather in Bowling Green (Kentucky), a U.S. flag is waved among the tornado damage.
Getty Images – GUNNAR WORD

Scientists believe that it is difficult to determine how climate change has an effect on tornado frequency. Their understanding of the matter is still in flux. However, they say that the atmosphere conditions which give rise to tornadoes is increasing in winter due to global warming. And tornado alley is shifting farther east away from the Kansas-Oklahoma area and into states where Friday’s killers hit.

Here’s a look at what’s known about Friday’s tornado outbreak and the role of climate change in such weather events.


Tornadoes form as vertical, whirling air columns from thunderstorms that stretch to the ground. They are fast and destructive, and can destroy everything they come across.

Thunderstorms are caused by colder and denser air being pushed against warmer, more humid air. Scientists call this atmospheric instability. An updraft occurs when 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.

This causes the wind to spin, which is what creates a tornado. For especially strong tornadoes, changes are needed in both the wind’s speed and direction.

Warm weather was a crucial ingredient in this recent tornado outbreak, but whether climate change is a factor is not quite as clear, meteorologists say.
The recent tornado outbreak was driven by warm weather, however, it’s not clear if climate change played any role.
Scott Olson via Getty Images

“When considerable variation in wind is found over the lowest few thousand feet of the atmosphere, tornado-producing ‘supercell thunderstorms’ are possible,” said Paul Markowski, professor of meteorology at Pennsylvania State University. “That’s what we had yesterday.”

There’s usually a lot of wind shear in the winter because of the big difference in temperature and air pressure between the equator and the Arctic, Gensini said.

But usually, there’s not a lot of instability in the winter that’s needed for tornadoes because the air isn’t as warm and humid, Gensini said. It was this time.


These are just a few of the factors that meteorologists will be continuing to research.

The warm and moist atmosphere that formed thunderstorms was brought about by December’s spring-like temperatures in the Midwest. La Nina is a phenomenon that brings warmer than average winter temperatures to Southern U.S. Scientists also anticipate unusual, warm weather in the winteras the earth heats.

“The worst-case scenario happened. Warm air in the cold season, middle of the night,” said John Gordon, a National Weather Service meteorologist in Louisville, Kentucky.

Experts say that the strong wind shear created by the storm prevented tornadoes dissipating once it had formed. Storm surges that lose energy are believed to cause tornadoes to disintegrate.

An overturned passenger van rests in an empty field in a rural neighborhood that was ravaged by a tornado in Mayfield, Kentucky.
The remains of an overturned van for passenger transport is seen in an undeveloped field near a Mayfield tornado-ravaged neighborhood in Kentucky.
Brett Carlsen via Getty Images

Gensini explained that although tornadoes lose energy usually in minutes or less, this one lost it for hours. That’s partly the reason for the exceptionally long path of Friday’s storm, going more than 200 miles (322 kilometers) or so, he said. Record was 219 miles (352 kilometers), set in 1925 when a tornado struck four US states. Gensini predicts that the record will be broken when meteorologists analyze it.

“In order to get a really long path length, you have to have a really fast moving storm. This storm was moving well over 50 miles (80 kilometers) per hour for a majority of its life,” Gensini said. That’s not the speed of the winds, but of the overall storm movement.

“You’re talking about highway-speed storm motions,” Gensini said.


It’s complicated. Scientists are still trying to sort out the many conflicting factors about whether human-caused climate change is making tornadoes more common — or even more intense. About 1,200 twisters hit the U.S. each year — though that figure can vary — according to the NOAA National Severe Storms Laboratory. There are more twisters than any other country.

Attributing a specific storm like Friday’sThe effects of climate changes remains very difficult. Harold Brooks from the National Severe Storms Laboratory, an expert on tornadoes and a scientist in the field of tornadoes said that less than 10% produce severe thunderstorms.

Scientists observed that the fundamental ingredients for a storm are changing as our planet heats. However, scientists have noticed these changes. Gensini says in the aggregate, extreme storms are “becoming more common because we have a lot warmer air masses in the cool season that can support these types of severe weather outbreaks.”

Brooks stated that the U.S. will likely see more tornadoes in winter as the national temperature rises above the long-term mean. He said that less events would occur during the summer.

Furtado of University of Oklahoma stated that tornado alley has moved eastward to the Mississippi River Valley. This is a term which was used to refer where twisters have hit the U.S. The shift was caused by an increase in temperature and moisture, as well as shear.

“Bottom line: The people in the Mississippi River Valley and Ohio River Valley are becoming increasingly vulnerable to more tornadic activity with time,” he said.


Follow Suman Naishadham @sumannaishadham & Seth Borenstein @borenbears


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