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Tornado FAQ's

We do get tornadoes in the UK. Here we aim to answer some of the most frequently asked questions regarding UK tornadoes. Should your question not be answered here then please get in touch.


- What is a Tornado ?
A tornado is a rapidly upward rotating vortex of air similar to a helix. The tornado extends down from a parent cumulonimbus* cloud and is also in contact with the land. The rotation can be very violent reaching wind speeds of over 300mph. If the vortex extends down from its parent cloud and touches a water surface then it becomes a waterspout. If the funnel reaches downward but doesn't touch the surface at all then it is a funnel cloud.

* Not all tornadoes form in cumulonimbus clouds.

- What Causes a Tornado ?
There are several different atmospheric conditions that must come together
to favor the formation of a tornado. The main variable is wind shear, which
is changes in the wind direction e.g. veering or backing and changes in the
wind speed at different heights in the lower atmosphere. Strong cold fronts
can make excellent breeding grounds for tornadoes, especially near coasts
as we have seen in recent years*. When the conditions are favourable
rotation may occur in severe thunderstorm cells*. Where the thunderstorms updraft,
downdraft and helicity converge a tornado may form.

* Tornadoes do not always develop when conditions are right.
* Funnel clouds have been known to form in strong cumulus cells.

- Do We Get Tornadoes in The UK ?
Yes!. On average the UK might see up to 33 (usually more) reported damaging tornadoes every year. Some years the total can be far lower or much higher than this. For example in 1982 there were 150 reported tornadoes.This may seem very low when compared to figures from the United States, however we must not forget that the USA is 39 times larger than the UK. Because of this difference in size, we must consider land area. It was recognized by the American Scientist Dr. Ted Fujita (who devised the F-Scale) that the UK has more tornadoes per unit area than any other country in the world.

- So Why Have I Never Seen One?
The confirmed tornadoes reported each year are quite often very widely
scattered, so are only witnessed by very few people. It is likely that
we have more tornadoes but they go unreported and unseen because they
will be weak lasting only seconds, occur in open countryside, be shrouded
in precipitation or hidden by our topography or structures such as buildings.
There are many people in the USA who have also never seen a tornado.

- Why Are American Tornadoes Stronger?
The USA has the extremes of atmospheric conditions required to produce large or strong tornadoes due to its location. Three types of airmass, cool air from Canada, Dry air from the Deserts and moist air from the Gulf of Mexico, all collide over the central United States. This causes very severe storm systems from which tornado producing thunderstorms are born. However it is a fact that the average American tornado and the average British tornado are almost identical.

- How are Tornadoes Measured?
We measure the itensity of tornadoes by the damage they do. This is done by investigating damage sites after a tornado has occured. We then compare observations with the T-Scale.

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Revised: February 23, 2006.

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