Tornado Fact 2. Tornadoes are measured and rated using the Fujita scale.

Tornado Fact 3. Tornadoes tend to occur in mid-latitudes, and as they are restricted to land masses this means mainly in the northern hemisphere.

Tornado Fact 4. Moist Gulf air from the south colliding with cold air travelling down from the north west, producing ideal tornado forming conditions. As a consequence the most violent storms are found over the North American continent.

Tornado Fact 5. On some days up to 20 tornadoes may be spotted in Tornado Alley- the flat country of the mid-west stretching from Texas through to Oklahoma and Kansas.

Tornado Fact 6. A wind speed of 280mph was ascribed to a tornado that hit Texas in April 1958

Tornado Fact 7. The average life-span of a tornado is approximately 15 minutes. However some can last much longer, on 26th May 1917 the Mattoon-Charleston Tornado lasted seven and a half hours and travelled 293 miles.

Tornado Fact 8. During 3rd and 4th April 1974, a 'super Outbreak' of tornadoes saw 148 individual tornadoes cross and devastate an area from Alabama to Michigan.

Tornado Fact 9. Most tornadoes travel from south-west to north-east, although they can and do travel in any direction.

Tornado Fact 10. The US endures around 750 tornadoes annually.

Tornado Fact 11. Tornadoes can occur at any time of the year, although there tends to be a peak in the US in Tornado Alley during May and June.

Tornado Fact 12. You would be extremely lucky to survive seeing the inside of a tornado vortex. Bill Keller from Kansas survived such a vortex in June 1928: "A screaming, hissing sound came directly from the end of the funnel, and when I looked up I saw right into the very heart of the tornado...it was brilliantly lit with constant flashes of lightning...around the rim of the vortex, small tornadoes were constantly breaking away and writhing their way around the funnel"

Tornado Fact 13. The inside of the funnel contains extremely low pressure equal to the pressure difference between ground level and an altitude of 4,900 feet - giving huge suction power

Tornado Fact 14. In the town of Natchez, Mississippi, in 1840 a tornado one mile wide touched down killing 48 people on land and drowning a further 269 in river boats and steam ships on the Mississippi river.

Tornado Fact 15. A waterspout is a tornado that occurs over water rather than land. However they are generally less violent, and will not move systematically northeastwards like a tornado would.

Tornado Fact 16. A bridge is not a good place to shelter from a tornado! Generally the confined space will increase the overall wind speed. This is despite well known TV footage of a news crew sheltering under a bridge. They did not receive a direct hit from the tornado and the bridge was of a rare design where they could crawl amongst the exposed girders for shelter and grip.

Tornado Fact 17. The most northerly tornado ever observed was on August 26th, 1976 at Kiana, Alaska, 54 miles north of Anchorage.

Tornado Fact 18. Well this is advice, more than fact. If you are caught out in the open by a tornado with no nearby buildings to shelter in, lie in a ditch, or lowest possible area, and protect your head and neck with your arms. Then pray.

Tornado Fact 19. Tornadoes are transparent, and appear so in the early stages of development, until dust and debris are picked up and give them colour.

Tornado Fact 20. Only 2% of tornadoes are classed as violent (F4 and F5), but these account for 70% of all tornado deaths.

Tornado Fact 21. 70% of all tornadoes are weak (F0 and F1), and account for less than 5% of all tornado deaths.

Tornado Fact 22. 50% of all fatalities from tornadoes occur amongst residents of mobile homes.

Tornado Fact 23. Hurricane Beulah spawned 115 tornadoes over Texas in September 1967.