Tornadoes are a spectacular but destructive natural phenomena that are capable of ripping apart buildings, uprooting trees and hurling vehicles and debris in a violent vortex of powerful winds. For most in the UK, this type of natural hazard is a foreign concept - an event that only strikes in the ‘Tornado Alley’ of the US or the outbacks of Australia. However, they are more prevalent in Britain than it may seem.
Before discussing tornadoes in the UK, it is important to understand what they are and how they form.
According to the Encyclopedia Britannica, tornadoes are “a small diameter column of violently rotating air developed within a convective cloud and in contact with the ground” and they “occur most often in association with thunderstorms during the spring and summer in the mid-latitudes of both the Northern and Southern Hemispheres.” This definition largely describes, in scientific terms, the land-anchored spiral a person would imagine when picturing a tornado in their head - nothing new there.
Tornadoes form when warm, humid air collides with cold, dry air, creating instability and strong vertical wind shear in the atmosphere. Wind shear is the change in wind speed and direction with height, which can cause the air to rotate horizontally (hence the spiral shape). Tornadoes can vary in size, shape, intensity, and duration, but they are usually measured by the Enhanced Fujita Scale, which ranges from EF0 to EF5. This measure is mainly based on the wind speed and the extent of damage. The strongest tornadoes can have wind speeds of more than 200 mph and can last over an hour.
Going back to our definition, tornadoes are often linked to thunderstorms and here is why: when a thunderstorm develops, the rising warm air tilts the horizontal rotation into a vertical axis, creating a rotating updraft (imagine a column of air that is spinning as it rises upward, a spiral essentially) called a mesocyclone. Meanwhile, cold air sinks and this movement of air supplies energy to the clouds. If the mesocyclone becomes strong enough, it can produce a tornado near the base of the thunderstorm.
Tornadoes are commonly found at middle latitudes, where the conditions for thunderstorm development are most favourable. The United States, famously, has the most tornadoes of any country, as well as the strongest and most violent ones. A large portion of these tornadoes form in an area of the central United States known as Tornado Alley (which I previously have mentioned), where warm, moist air from the Gulf of Mexico meets cold, dry air from the Rocky Mountains. Canada experiences the second most tornadoes, especially in Ontario and the Prairie Provinces. Australia has seen some tornadoes in the regions of Queensland and New South Wales. All of these countries implement tornado drills as part of emergency preparedness in schools, although the training is similar to earthquake drills - taking cover for protection against debris.
The UK sees a surprising amount of tornadoes, with roughly 30 to 50 appearing each year - the most for any country per square mile! However, most of them are weak and short-lived and rarely cause significant damage. The UK tornadoes are usually rated as EF0 or EF1, with wind speeds of less than 112 mph, and only last for a few minutes. They are often associated with squall lines, which are bands of rain showers and thunderstorms that move across the country, or with low-pressure systems that bring unsettled weather.
Britain's most recent tornado, as of writing this article, occurred in Littlehampton, West Sussex and was on 29 October 2023, during Storm Ciarán, and ripped the roof off a house. A resident was taken to hospital due to the shock of the event. In the English Channel, the island of Jersey (part of the British isles, but a crown dependency and not part of the UK - like the Isle of Man) was hit with a significant tornado on 6 November 2023, also during Storm Ciarán. The storm brought gusts of up to 104 mph and caused major damage to homes, schools, and organisations. More than 150 residents were displaced, and three people were taken to hospital. TORRO estimated that the tornado was a “strongly devastating” tornado with wind speeds of up to 168 mph. This made it the most powerful tornado recorded in the British Isles since 1954, when a 200 mph tornado hit Gunnersbury in London.
The UK’s most damaging tornado was on 28 July 2005, when a tornado struck Birmingham, injuring 19 people and causing damage that cost an estimated £40 million to repair. The tornado had wind speeds of up to 145 mph and travelled over four miles from its formation point (this distance travelled is known as the track length of a tornado). It affected several areas, including Balsall Heath, Small Heath, Moseley, Sparkbrook, and Kings Heath. The tornado damaged more than 1,000 buildings, including houses, shops, factories, and churches. It also uprooted hundreds of trees and overturned cars and buses.
In summary, tornadoes can occur in many parts of the world, including the UK, and are a fascinating but dangerous occurrence to witness. Although UK tornadoes are usually weaker and less frequent than those in other countries, they can still pose a threat to people and property. It is worth being aware of the signs of a tornado just in case, including dark clouds, strong winds, hail, or a loud roar. Take shelter in a sturdy building if possible or lay flat on the ground.