The tornado that swept through Kensal Rise was a medium-sized twister by British standards. Reports of the level of damage to trees, roofs and cars indicate wind speeds of about 100mph (160km/h), a T3-T4 strength tornado on a scale from T0 to T10 developed by the Tornado and Storm Research Organisation (Torro).

In fact, Torro had issued a forecast alert of thunder, hail, lightning and tornado as conditions in the southern half of Britain turned convective. This meant that air was rising through the atmosphere and, as a surge of warm, moist tropical air hit the colder drier air higher up, exploding into thunderclouds.

The consequence was a squall line, a violent band of thunderclouds, which tore across southern England during the morning. This was driven on by a vigorous jet stream, a river of wind several miles high. Also crucial for the development of a tornado, the winds in the atmosphere were coming in different directions yesterday and set the air inside a cumulonimbus cloud spinning, rather like whirling a child’s spinning top.

As a vortex created within the cloud grew increasingly narrow, it spun faster — rather like ice skaters spinning faster as they flatten their arms against their body — until eventually a funnel-shaped cloud grew from the bottom of the thundercloud and touched the ground with violently rotating winds, a tornado.

Such incidents in this country are often incorrectly called “mini-tornados” in the media. In fact, tornados in Britain are not small in size and can be as powerful and destructive as the infamous twisters of Tornado Alley in the American Midwest.

In July 2005 Birmingham was struck by one of the most brutal tornados recorded in this country, with wind speeds estimated to have reached over 225km/h (140mph), which blasted out shop fronts, roofs were ripped off, buildings collapsed, more than a thousand trees were felled, and 19 people were injured. The damage was estimated at £39 million.

Tomorrow is 52 years to the day since another violent tornado appeared in west and northwest London. A huge thunderstorm drove in from the South Coast, the sky turned ink-black and a tornado touched down at Bushey Park, near Hampton Court, smashing down trees.

At about 5pm, the storm reached Chiswick, in West London, with a huge conical cloud hanging from the sky, green lightning flashing from its sides and a deafening roar like an express train. The tornado blew Gunnersbury station apart then demolished two factories and drove on through Acton, not far from BBC Television Centre, to Willesden, near Kensal Rise.

Roofs on houses were ripped off, chimneys crashed down and walls collapsed. A car was hurled through the air while terrified people outside ran for cover as bricks, glass and wood shot through the air like missiles. Newsreels of the day show a scene of devastation described as looking like something from The Blitz. In all this mayhem, it is incredible that there were only a few minor injuries.

The past few years have seen a number of notable tornados in Britain. However, there is no evidence that the number or intensity of tornados is rising here or elsewhere in the world, because of global warming.

Tornados in Britain

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