Tornadoes remain among the most complex and least understood weather phenomena. Scientists still lack full answers about how they form, how they sustain themselves and why they dissipate. Wind speeds can range from about 60 mph to more than 300 mph.
Tornadic activity typically tapers off after the summer months, but the threat doesn’t disappear. The destruction left across Tennessee in December 2023 serves as a reminder of the risk.
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Tornado threat persists
Forecasters expect roughly 28 tornadoes in the U.S. this December.
“The United States has more tornadoes and greater tornado density than any place in the world. We have a very unique geography,” said Walker Ashley, an atmospheric scientist at Northern Illinois University. “The proximity of the Gulf of Mexico and the western Caribbean brings moisture into the U.S., which is a critical ingredient for thunderstorm formation. And the mountains to the west create an environment supportive of very strong instability, or energy, for thunderstorms.”
Atmospheric pressure plays a central role. Lower pressure strengthens storms by drawing air inward, producing the rain, wind and rotation that can lead to a funnel cloud.
Tornado outbreaks are most common between February and June. But a strong low-pressure system combined with unusually warm air can produce a winter tornado.
“Most tornadoes are short-lived — sometimes only minutes — and may not travel far,” Ashley said. “In other cases, particularly during the cool season, tornadoes tend to move very fast.”
Tornado preparedness
Winter conditions can make an already dangerous event more hazardous.
The National Weather Service advises residents to bundle up before taking shelter, restock safe spaces with winter supplies, keep access routes clear and prepare for possible power outages.
The December 2023 tornado outbreak killed seven people and injured 71.
