The region’s been hearing a lot about tornadoes.

There was the great 3 a.m. tornado alert that awoke the region and generated countless memes in April, while just a month later, tornadoes were recorded along the Montgomery County-Berks County and Bucks County-Lehigh County borders. Tornadoes have also swept across the central United States this spring, turning deadly, injuring scores of people, and wreaking destruction.

While nearly three-quarters of tornado warnings are “false alarms," here’s what you should know, from what a tornado is to the difference between a watch and warning:

What’s a tornado?

The National Weather Service defines a tornado as a “violently rotating column of air extending from the base of a thunderstorm down to the ground.” Tornadoes typically last for less than 15 minutes but can cause a lot of destruction with winds that can reach more than 300 mph, according to the weather service.

“Fifteen minutes is a long time for a tornado to be on the ground," said Valerie Meola, a meteorologist with the service in Mount Holly. “Most of our tornadoes are not on the ground for nearly that long.”

It’s those high wind speeds and ability to cause debris to go flying that make tornadoes so dangerous, according to the weather service. They’re called “nature’s most violent storms." Though, mountainous terrain, like in some parts of Pennsylvania, could help a storm dissipate faster than it would across the Plains.

“We do get tornadoes here, they’re not as common, but we’ve seen our fair share this season so far," Meola said.

How does a tornado form?

The truth is that we don’t know for sure, but we can say that severe tornadoes are caused by supercells — or “rotating thunderstorms with a well-defined radar circulation called mesocyclone,” according to the weather service.

Tornadoes are often recognized by their funnels, and there’s often a calm felt before the storm — with the air turning very still before a tornado makes its way through the region. Hail is not uncommon, either.

A graphic representation of how tornadoes are formed.
Francois Duckett / AP
A graphic representation of how tornadoes are formed.

Is a twister the same thing as a tornado?

The two terms are used interchangeably.

“They’re very similar," Meola said. "Tornado is more, I guess, the official term that we use, but twister is a term a lot of people know as well.”

What’s the difference between a watch and a warning?

Hearing about a tornado watch or warning in your area can be scary, but there are differences between the two. A watch, as declared by the Storm Prediction Center, means that weather conditions capable of producing tornadoes are possible, according to the weather service. A warning, issued by your local forecast office, means a tornado has been spotted and “there is imminent danger to life and property.” Think of a watch as a cautionary message while a warning is when you should seek shelter.

Of course, watches vs. warnings aren’t applied to just tornadoes. For the Philadelphia area, you probably associate them with severe thunderstorm watches and warnings.

“A watch can be described as it could happen," Meola said. “It means that the conditions of the atmosphere say we could see severe storms or there’s potential for tornadoes. A warning means imminent. Means it’s occurring, on its way, take shelter, it’s more of an immediate thing.”

An illustration showing the difference between a watch and a warning.
National Weather Service / Screenshot
An illustration showing the difference between a watch and a warning.

Thunderstorm vs. ‘severe thunderstorm’

The weather service only issues alerts for a “severe thunderstorm." Meola said there’s certain criteria that needs to be met for a storm to be deemed “severe,” including winds 58 mph or greater, or hail with a one-inch diameter or greater — think the size of a quarter.

A regular thunderstorm? Those are just the typical rain and lightning you see throughout the summer.

“Lighting does not make a storm severe," Meola said. "It is a part of every thunderstorm.”