Analysis: We don't yet fully understood the science of tornadoes, but we get a surprising number of them in Ireland every year
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In 2023, a 'mini-tornado' tore through Leitrim village. It hit around lunchtime on December 10th and left cars buildings, boats, and trees in the area badly damaged. The term 'mini-tornado' is used to distance these weather events from the larger tornadoes recorded in the US and other countries.
More than 300 tornadoes hit the European region every year, though the European Severe Storms Laboratory received nearly 800 tornado reports in 2022. The low countries, Germany, Southern Scandinavia, parts of Italy and Central England have the highest reported occurrences in Europe. The Fujita-scale of tornadoes, in use since 1971, classifies tornadoes from F0 (least severe) to F5 (most severe). The last F5 tornado within the European Union was in Palluel in northern France on 24 June 1967.
But what's the story with Ireland? And what exactly is a tornado? Let's take a look at the science. What is believed to be Ireland's first documented tornado occurred near Rosdalla, Kilbeggan, Co. Westmeath on April 30th 1054 and is documented in the Annals of the Four Masters. Today, tornadoes in Ireland are still surprisingly common (to the uninitiated, that is), according to Dr Noel Fitzpatrick, research meteorologist with Met Éireann.
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From RTÉ News, localised tornado causes damage in Leitrim village
How many tornadoes a year do we get in Ireland?
"The number that's often quoted is in or about 10 per year. That's a fairly rough number because many of these things could easily form quite quickly and disappear just as quickly, and sort of blow themselves out in in fields and places that people don't notice."
They disappear as quickly as they appear. Does that make them difficult to detect?
"Absolutely. There are certain conditions that you require for tornadoes to form, but there's absolutely no guarantee that they will form. In fact, their formation still isn't fully understood, so they can be difficult to predict and then to detect, as well," says Fitzpatrick.
Does Met Éireann rely on eyewitness accounts?
"In terms of reporting that's very useful. Because we can then go back and look at the conditions at that time and maybe confirm if the conditions were there that could have caused it. It's also helpful because there are other things - strong winds - that can cause damage, that could be misinterpreted as tornadoes. Sometimes you can sort of reassure people that it wasn't a tornado, the conditions weren't there at that time."
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From RTÉ Archives, Damien Tiernan reports for RTÉ News on a mini-tornado tearing through homes in Glengoole, Co Tipperary in 2006
So what is a tornado? What causes them to form?
"The general description for a tornado is a strongly rotating column of air, that's in contact with both the cloud above it and the ground as well," he explains. "If it's only coming down from the cloud and hasn't touched the ground yet, it's more commonly referred to as a funnel cloud."
We need a few different ingredients for a tornado to form. The first is a thunderstorm, and for a thunderstorm to form, we need a few "key conditions". "The first is you need moisture, which we have plenty of in the atmosphere around Ireland. Moisture is like the fuel for a thunderstorm. You also need unstable air, and what I mean by that is, basically you have a warm air sitting below colder air above it."
To understand how thunderstorms kick off, it helps to consider a pot of boiling water. The bottom of the pot is in contact with the stove top's heating surface. It starts to heat up and so does the water inside the pot. "It starts to heat up and it starts to bubble and it wants to rise up through the colder water. That's called convection. It's exact same thing in the atmosphere, where you’ve got warm air below colder. It wants to rise and it starts to bubble up. That gives you these sort of fluffy clouds that you can see sometimes on a sunny day, called cumulus clouds," Fitzgerald says.
From National Geographic, how tornadoes form, how they are rated and where the most intense tornadoes occur
"The third ingredient for those thunderstorms to form, is you need something to sort of kick off that rising process. It might be something like a 'weather front' where you’ve got a boundary between one type of air and another type of air. Say for example a cold front, where you've got a cold air coming in. That could be enough to act as a wedge to kind of lift up the air and almost give it a little kick start to start rising."
Finally, for the thunderstorm to bring forth a tornado, we need rotation." So we get lots of thunderstorms in Ireland, but we don't get a whole lot of rotating thunderstorms and that's the special ingredient," he explains. "Your thunderstorm will rotate if you have wind speeds varying as you go up in height."
"A way to think about that is, say you've got a a pen in your hand and you're moving your hands in different directions. The pen is gonna roll in between them so if you've got air and wind blowing at different speeds, or even different directions, as you go through the atmosphere, the air is going to roll in between. So you get this rotational energy. It's rotational energy getting pulled into a thunderstorm, that's the ground for generating a a tornado."
Is there a time of year that we’re more prone to get thunderstorms in Ireland?
We can get thunderstorms all year round, says Fitzgerald. "In other parts of the world they’re more commonly associated with the warmer seasons because you're getting that hot air at the ground level and you need that hot air to start rising. But in Ireland we can get thunderstorms all year round, because it’s the relative difference between the warm and the cold air. We got a lot of cold air above us, particularly during the winter, so the air at the ground seems warm relative to that cold air, and it wants to rise. So we often get thunderstorms in the winter as well. It can happen anytime."
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From RTÉ Radio 1's Morning Ireland, Senior Forecaster with Met Eireann Gerry Murphy on what causes a weather event like a localised tornado
Are there parts of Ireland more likely to see tornadoes?
"Not really. Ireland is quite a small country, so generally weather patterns, for the most part, affect the whole island. You can get features where, sometimes to have thunderstorms kick off, you need something to give it a little bit of a lift or a little bit of kick to get started. What can cause that is air flowing over hills or mountains. So we often see thunderstorms forming downwind from where we have, say, some of our mountain ranges or coastal hills. So they can be locations for formation."
In countries like the US, on the central plains, they get over a thousand tornadoes per year, but they can still take everyone by surprise. "They have incredible networks of weather radar specifically for detecting these kinds of severe weather. And yet, they still cause billions of damage every year, you still unfortunately have fatalities."
"So while we are getting a grasp on the cause of them, they’re extreme and they can be random events. They're tricky to predict. We're gradually narrowing in the reasons for why they occur and when they're going to occur, but it's still very much a working science, even in these countries where they get them very regularly."
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The views expressed here are those of the author and do not represent or reflect the views of RTÉ
