Tornadoes in the UK
17th October, 2014
Whilst winter weather is always at the forefront of our minds, it is difficult not to be interested in all forms of meteorological phenomenon; both in the UK and around the world. For that reason our attention was caught when news came through last week of a tornado touching down in the north of England.
Many people assume tornadoes to be a phenomenon associated with the United States but, whilst the US may receive more tornadoes annually, you may be surprised to know that the UK experiences more tornadoes per square metre than any other country in the world. On average we see between 30 and 50 tornadoes in this country every year and, whilst the majority are far weaker than their American counterparts, the one that touched down in Alfreton last Wednesday was strong enough to tear the roof from a property and damage several vehicles.
Now whilst no two tornadoes are ever the same, they all require a certain combination of intense and unseasonal heat in which to form. When these conditions come together, most tornadoes follow a similar process to form.
- As ground temperature increases the moist air above it is slowly heated, causing it to rise.
- As the warm moist air rises it comes into contact with cold dry air. The warmer air punctures the layer of cooler air above, causing a thunder cloud to form.
- A storm will develop, causing rain, thunder and lightning.
- As the storm develops it causes the upward movement of air to become very rapid. At the same time, winds from different directions can cause the column of air to rotate.
- Once this happens a visible funnel will drop out of the cloud in the direction of the ground.
Depending on its intensity a tornado can last anything from a matter of seconds to more than an hour. The average lifespan of a tornado is 15 minutes, though the majority are relatively weak and will last between two and five minutes.
Once a tornado forms the winds within it can be so fast that it is not possible to accurately measure their speed. Instead a damage scale, known as the Fujita Scale, was developed to help estimate the speed of tornados. The scale ranges from F0 where winds of between 0 and 73mph are expected, to devastating F5 tornadoes that feature winds in excess of 260 mph.
Since 1950 there have been 67 tornadoes globally officially rated as F5:
- 59 in the United States
- 2 each in France, Germany and Italy
- 1 each in Canada and Russia
The most recent F5 storm occurred in May 2013 when a tornado hit Moore, Oklahoma in the United States. Numerous homes were swept away, including 9 that were bolted to their foundations. An elementary school was levelled; two 10-ton propane tanks were thrown more than half a mile and an oil tank was thrown a full mile from its production site. A second oil tank was thrown so far that it was never found after the storm.
The video below was recorded for National Geographic and shows the birth of a tornado in south-central Kansas, filmed just two days before the devastating F5 tornado in Oklahoma.