Tornado outbreak ravages the country for third December in a row

A terrifying tornado outbreak over the weekend that killed six people, injured dozens and left thousands without power made this the third consecutive December with a spate of deadly tornadoes.

Tornadoes can happen during any month of the year in the United States, but emerging research suggests that as the climate warms, an increasing number of tornadoes may strike during traditionally cooler months.

A powerful storm system struck Tennessee on Saturday, spawning multiple tornadoes across the state. Nashville and the town of Clarksville were hardest hit.

Strong and changing winds at different heights in the atmosphere, also known as wind shear, were a key ingredient that fueled this weekend’s tornado outbreak, promoting “spin” in the atmosphere to form tornadoes. That combined with warmer-than-average temperatures — as much as 20 degrees Fahrenheit warmer than average in some areas — to create tornado conditions.

The National Weather Service in Nashville confirmed that a 150 mph EF3 tornado ripped through the area, carving a 43-mile path into Kentucky. Tornadoes are classified according to what’s known as the Enhanced Fujita Scale. The weakest tornadoes, EF0 and EF1, have winds of up to 110 mph and typically cause relatively light damage. The most powerful tornadoes, EF5s, have winds above 200 mph and usually cause catastrophic damage.

The Clarksville tornado killed two adults and one child, and injured more than 60 others. Forecasters said the tornado was on the ground for over an hour, adding that it was the strongest confirmed tornado of the outbreak so far. Surveys are ongoing to determine how many other tornadoes touched down during the storm.

An EF2 tornado with maximum estimated winds of 125 mph was also confirmed by the National Weather Service in Nashville. This tornado caused damage in Madison, Hendersonville and Gallatin — all communities located northeast of Nashville.

The weekend’s tornado outbreak adds to a growing trend of deadly tornado outbreaks in December.

In 2021, a tornado outbreak that spanned Dec. 10 and 11 produced 66 tornadoes. During that event, an EF4 tornado struck Mayfield, Kentucky, reaching maximum estimated winds of 190 mph and carving a 165.7-mile path. At the time, it was nicknamed the “quad-state storm,” because the parent thunderstorm that produced the destructive tornado crossed four states: Arkansas, Missouri, Tennessee and Kentucky. The resulting tornado also stayed on the ground continuously across three states.

Later that month, another tornado outbreak on Dec. 15 produced more than 60 tornadoes.

The following year, in December 2022, a spate of tornadoes tore through Louisiana from Dec. 13 to Dec. 15. More than 50 tornadoes were confirmed during that outbreak, including a damaging EF2 tornado that hit New Orleans on Dec. 14. The strongest tornado of that outbreak was an EF3 that struck Union Parish, near the town of Farmerville.

Tornadoes in the month of December are not uncommon, and the Southeast and Gulf Coast regions are no stranger to these kinds of winter-season storms.

But research suggests that there is an increasing likelihood of tornadoes in cooler months as a result of climate change.

One study in 2018 that focused on cold-season tornadoes (defined as November through February) found an increasing trend in winter tornadoes across much of the southeast, with a bull’s-eye in western Tennessee.

A study published in 2021 found that due to the warming atmosphere, tornado-favorable environments during the winter months have increased across the southern United States.

While scientists can’t link one single outbreak event to climate change, the background meteorological factors that led to the event, such as warmer-than-average temperatures, likely contributed to the severity of the thunderstorms and tornado outbreak.

With winter being the fastest-warming season across the United States, a warming climate could mean more tornadoes during the months of December, January and February in the years to come.