Sunday 14 January 6.40pm
Extreme weather, storm chasers and tornadoes are things we normally associate with the American Midwest. A huge belt of America, from Texas in the south to North Dakota in the north, experiences tornadoes so frequently that it has become known as Tornado Alley. But Britain too has its own history of twisters.
On 7 December 2006, a tornado hit Kensal Rise in London. Winds of up to 120mph caused extensive damage to an area of the country rarely associated with extreme weather phenomena. An even larger tornado struck Birmingham in 2005. The astonishing truth is that Britain has more tornadoes per square mile than any other country in the world.
A tornado is a vortex of wind that can move along the ground at 70mph, sucking up everything in its path. The wind speeds within the vortex are usually more than 100mph but they can get as scary as 300mph.
Tornadoes form where cold air currents and warm air currents collide. When this happens the warm air rises creating an area of low pressure beneath it. Cold air rushes into the low pressure system and causes winds to form.
Tornado Alley storms are a consequence of warm humid air traveling north from the Gulf of Mexico colliding with cool dry air travelling south from Canadian Rockies. These two air currents meet over relatively flat terrain in the middle and create havoc – literally.
British tornadoes are blown in from the Atlantic, where most of our stormy weather originates. Warm air currents follow warm water currents of the Gulf Stream up from the tropics and meet icy currents and cool air coming down from the Arctic. These currents collide and form low pressure weather fronts just off Greenland which are carried to Britain by the jet stream.