Tornado defined A tornado is a violent, twisting storm known for damaging winds. It has a funnel appearance and occurs in thunderstorm clouds (often these are a special type of thunderstorm cloud called mammatocumulus clouds) Power of a tornado A tornado typically measures a few hundred yards in diameter and contains winds up to 200 mph. They are dangerous storms that can lead to vast destruction. They typically move between 10 and 20 mph and last less than an hour and may move only 20 total miles. However, destructive tornados can last for hours, measure more than a mile in diameter and can move more than 200 miles with winds of 60 mph. Movement In the northern hemisphere, the winds of a tornado whirl in a counter-clockwise direction. In the souther hemisphere, the winds of a tornado whirl in a clockwise direction. As for tendencies of movement, in the United States, most tornados travel in a northeasterly direction Storm chasing Storm chasers are people who track thunderstorms, often on the ground, to record them, learn about them, or just for the sheer thrill. Storm chasers know that tornadoes can be found throughout the world, but the United States has most of them, with nearly 700 per year. Formations Most tornadoes develop in the mid spring and summer as cool Canadian air meets the warm Mexican air that moves into the U.S. after winter (usually the midwest part of the U.S.) . A front often forms, with cumulonimbus (thunderstorm) clouds. By afternoon or evening, such skies might be energized as warm, moist air rises rapidly over the cold air. With such a rapid rise, a circular wind movement might develop, giving birth to a funnel cloud (or clouds) moving out of the bottom layer of storm clouds. By this time, the sky may take on a thick black or green color. Hail, vivid lightning, and heavy rain may have already begun to fall. And, hissinr or roaring sounds – a solid indication that a tornado is near – may be present. The funnel cloud may touch down, to form an official tornado, or it may remain a funnel cloud. Houses and tornadoes One of the reasons a house is not an ideal place in a tornado is that a tornado will suck up the air around the house. As it does this, the pressure outside the house drops, but inside the house, the pressure remains the same. This can cause an imbalance in air pressure and make the house blow apart. This is the reason that some scientists say a few windows should be left open if a tornado is near. Forecasting tornadoes Forecasting tornadoes is not an exact science. However, the development of Doppler radar in the last 20 years in particular, has helped people known when thunderstorm formation are likely. By looking for hooks and echoes in the radar, meteorologists can identify the foundation of a storm and issue warnings to people who may be in danger of having a tornado. Escaping tornadoes FThe best place to stay during a tornado is in a storm cellar designed for tornado protection. The next best place is a basement. People should be near the side of the room that the storm is approaching and, if possible, crouch beneath a table. If there is no basement, people should be on the bottom floor of a house or building. They should lay down, under a table or bed if possible, away from windows. Outside, people should find a low spot, such as a ditch to avoid debris that flies (though it still is possible to get sucked into the funnel). Mobile homes should always be vacated. Measuring the Destructiveness The Fujita Scale T. Theodore Fujita developed this scale for measuring tornadoes based on the amount and type of wind damage Rank ‡`��WInd speed in mph ‡`��Damage ‡`��Strength F-0 40 - 72 light weak F–1 73 - 112 moderate weak F-2 ‡ ��113 - 157 ‡ ��considerable ‡ ��strong F-3 ‡ ��158 - 206 ‡ ��severe ‡ ��strong F-4 ‡ ��207 - 260 ‡ ��devastating ‡ ��violent F-5 ‡ ��261 or more ‡ ��incredible ‡ ��violent |