Tornado climatology
The United States averaged 1,274 tornadoes per year in the last decade. April 2011 saw the most tornadoes ever recorded for any month in the US National Weather Service's history, 875; the previous record was 542 in one month. It has more tornadoes yearly than any other country and reports more violent (F4 and F5) tornadoes than anywhere else.
Climate of the United Kingdom
It is internationally recognised that the United Kingdom has a higher incidence of tornadoes, measured by unit area of land, than any other country in the world. Dr T. Theodore Fujita (inventor of the Fujita scale), an American meteorologist, was the first to recognise the UK as the top site for tornadoes in 1973. The United Kingdom has at least 33 tornadoes per year, more than any other country in the world relative to its land area. Although most tornadoes are weak, there are occasional destructive events, for example, the Birmingham tornado of 2005 and the London tornado of 2006. Both registered F2 on the Fujita scale and both caused significant damage and injury. The largest ever recorded was thought to have been an F4, again in London in 1091. The most deadly occurred on 28 December 1879. All 74 lives were lost when a passenger train plunged from the Tay Bridge (Tayside) into the Tay Estuary, when the middle section of the bridge collapsed. Although the bridge was poorly constructed and had already been weakened in earlier gales (including the pre-existing winds at the time of the tragedy), the ultimate failure is believed to have been caused by two or three waterspouts which were sighted close to the bridge immediately before the accident. A tornado also developed in London on 3 July 2007.
The UK also holds the title for the highest known 'outbreak' of tornadoes outside of the United States. The largest tornado outbreak in Britain is also the largest tornado outbreak known anywhere in Europe. On 23 November 1981, 105 tornadoes were spawned by a cold front in the space of 5.25 hours. Excepting Derbyshire, every county in a triangular area from Gwynedd to Humberside to Essex was hit by at least one tornado, while Norfolk was hit by at least 13. Very fortunately most tornadoes were short-lived and also weak (the strongest was around T5 on the TORRO Tornado Scale) and no deaths occurred.