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BY Wijke Ruiter

 

The National Weather Service (USA) reports Friday May 3, 2002:" More tornadoes for Maryland, Ohio. Meteorologists confirm that a tornado hit Maryland last night, the second to wreak havoc on the state in four days. Thunderstorms brought the tornado, large hail and heavy rain, damaging more than 12 homes and barns. trees snapped as the storm moved east... No one was injured"

For this weather-special we're crossing the Atlantic; for in Mid-West of the USA  the tornado-season has begun.

According to the National Weather Service a tornado is: "A violently rotating column of air in contact with the ground and pendant from a thunderstorm".                  

A tornado develops as every normal shower; but the process is far more faster and stronger in regions where air-masses with huge differences in temperature meet. In the USA this region is called the "Tornado Alley" where cold air-masses from Canada meet the warm, subtropical air from the Gulf of Mexico. The warm, moist air rises with high speed -so called updrafts -; a little low at the ground as result.    

The air -with water-vapour - around this low rotates          and cools down: the rotation will be visible while the vapour condenses. A jetstream at 5 to 6 miles height will give an impulse to this process, as the updraft is drawn away in this stream. (it works like a chimney). As soon as this circulation comes down to the ground a condensation funnel will be visible and the tornado is born. 
The funnel of the tornado is about 300 - 450 feet; but funnel of heavy tornado's can reach a diameter of 700 - 1500 feet. When a tornado passes its sounds like a dashing fast train. It takes about a few tens of seconds to 2 to 3 minutes; with heavy tornado's about 5 to 10 minutes. 

A tornado can be extremely violent; asking victims every year and bringing lots of damage to everything that is found on its path. The Japanese meteorologist Fujita has set up a tornado-strength-scale. The F0 is the lightest tornado with wind speed of 40-72 mph, the heaviest is F6 with wind speeds of 319-379 mph. The heaviest tornado's that occur in the Tornado Alley are F4 and F5; with wind speeds of 207-318 mph. Houses and cars are swept away, trees snap, huge constructions are damaged easily. Such F4 and F5's exist about a few hours leaving  a destructions-trail of  about 70 miles.  
Until now - may 5 2002 - there are 96 tornado's reported which were fatal for about 10 people. It may sound strange but that's good news: normally the first victims fall already in January and the number is over 20 by the end of April; with a normal number of reported tornados of 200 - 300.

Of course this extreme weather will also attract people to watch the scene. There are loads of storm chasers in America risking their lives to experience the omnipotence of nature. They leave us their stories and pictures.

You can find them for example on the following websites:
www.chaseday.com; www.stormchase.co.uk; www.stormtrack.org

 mailto:wijke@scribeweekly.com