Mini tornadoes which are capable of local-level destruction are unusually common across the UK but predicting them is a challenge, scientists say.
One recent small tornado that swept through Littlehampton on England’s south coast was strong enough to move cars and smash windows, and another such “dust devil”, caught on film in Southport in June, catapulted a child in a zorb ball into the air.
Dust devils are dust-filled vortexes of air spiraling upwards varying in height from just a few feet to over 300m (1,000 ft) but it remains unclear how they formed.
This freak weather phenomenon is driven by heat energy, where a cooler atmosphere is in contact with a warm surface, and they are mainly known to occur in desert and semi-arid areas, according to the UK Met Office.
They have been sighted more during heatwaves when the ground is dry and high surface temperatures produce strong updrafts.
Unlike tornadoes, the dust devils grow upwards from the ground rather than down from the clouds.
While they may last only a few minutes as cool air is sucked into the base, cutting off the mini tornado’s heat supply, the spiraling vortex of air may still cause damage to properties and injure people.
Tornadoes sweeping through the US are caught more widely on camera by storm chasers and make the news, but researchers studying these twisters say they’re also “surprisingly common” in the UK as well.
About 1.3 tornadoes are detected in the US per year per 10,000 square km every year, while in the UK this density is higher at around 2.3 per year, David Schultz from the University of Manchester in the UK writes in The Conversation.
Although this number in America can be higher for states in the “Tornado Alley” like Oklahoma or Kansas, researchers say a random location in the UK is still likelier to experience a tornado than a random place in the US.
Assessing data on sightings of these twisters in the UK from 1980–2012, scientists were able to put together a map of tornado hotspots in the country.
A 2015 study published by meteorologist Kelsey Mulder found that four corridors in England were most likely to have a tornado.
These included one from London and Reading, another from Bristol, north to Birmingham and Manchester, an area from Northeast of London to Ipswich, as well as a stretch of land in the South coast of Wales near Swansea.
“The UK’s tornado alley is really three regions, most in southern England: an area south of a line between Reading and London with a maximum near Guildford, locations southwest of Ipswich, and a line west and south of Birmingham,” Dr Schultz said.
These regions, scientists say, may see a tornado “as often as every 15 to 30 years.”
Tornadoes in the UK have mostly been found to be strengths F0 or F1 – with estimated wind speeds of up to 180 kph (112 mph) – with a few reported F2 category storms with wind speeds just over 250 kph (157 mph).
There have not been any devastating F5 storms, blazing at over 480kph (300mph) like the ones that hit the US coasts, causing widespread loss of life and damage to property.
But some large F2 tornadoes may also cause widespread damage.
For instance, one such tornado that struck Birmingham in 2005 injured 39 people and caused £40 million in damages.
However, the process by which these weak tornadoes form in the UK is not completely understood, scientists say.
In the UK, they say these mini-tornadoes often form from lines of storms along cold fronts.
Of the nearly 30 tornadoes occurring in the UK each year, 40 per cent develop on cold fronts, according to a 2020 study.
But scientists are still trying to work out reliable prediction methods to say which cold fronts are likely to produce tornadoes.
Researchers now have ways to identify some conditions in which the wind direction changes abruptly, sparking instabilities where even small perturbations can grow into large vortices.
“Such vortices are thought to be the precursor for tornadoes,” Dr Schultz says.
But to understand how tornadoes themselves form, he says more close-up chance observations of tornadoes and powerful computer programs to model the atmosphere may be needed.
