Transcript File
Mostly in large blocks called air masses. Air masses move slowly from place to place. Wherever they go, they bring a change in the weather. Wind is moving air. Warm air rises, and cool air comes in to take its place. This movement creates the winds around the globe. The windiest place in the world is Antarctica. Global air movement is caused by the Earth’s rotation and movement of warm air away from the equator. 3 Key Conditions required for thunderstorms to form: • (1) Moisture in the lower to mid levels of the atmosphere. (2) Unstable air That is, air that will continue rising once it begins rising from near the ground. (3) A lifting force Something is needed to cause the air to rise. The most common lifting force is heating of air near the ground. As air warms it becomes lighter and begins to rise. Advancing masses of cool air, which force warm air upward, also trigger thunderstorms. Check out this site to view satellite images of the earth and cloud movement. http://www.accuweather.com/mapssatellite.asp?partner=17490 How does a tornado form? A tornado begins in a severe thunderstorm called a supercell A supercell thunderstorm, is a thunderstorm with a persistent rotating updraft. Supercell A supercell thunderstorm is a huge rotating thunderstorm. These storms are the most likely to produce long-lasting tornadoes and baseballsized hail. Updrafts of warm air carry water droplets above the freezing level in thunderstorms. Once frozen it begins to fall but gets caught in another updraft. Eventually, the ice gets too heavy to be kept aloft by the winds and it falls as a hailstone. Hail often melts before it reaches the ground, but in some cases ice chunks the size of softballs pound the countryside. Most are the size and shape of small peas. But once in a while hailstones get quite large. In May 1926, hailstones the size of baseballs fell in Dallas, Texas. In just 15 minutes the hail caused $2 million in damage! More interesting facts. The biggest hailstone on record was as big as a medium-sized pumpkin. Luckily, it didn’t land on anyone’s head! This hailstone- 17.5 inches (44.5cm) around and weighing 1.6 pounds (753g), fell in Coffeyville, Kansas, on September 3, 1970. •Sad to say, the hailstones that fell on Bangladesh on April 14, 1986 is another story. •Some hailstones weighed up to 2.2 pounds (1kg)! The giant chunks of ice killed nearly 100 people. The clash of warm and cold air helps supply the humidity and energy needed to form a tornado. Winds from different directions high above the ground help supply more energy and also give the air the turning motion needed for tornadoes. What storm is smaller than a hurricane-but much more violent? • A tornado, or twister. The winds around the center of a tornado are the fastest winds on Earth. • Nature’s Most Violent Storms. The life of this tornado was 10 minutes. More pictures of tornadoes More pictures of a tornado. Twister is a nickname for tornado. Ideal circumstances for a tornado: • The terrain is relatively flat. • Warm humid air going north from the gulf of Mexico and cool dry air going south from Canada can easily crash into each other and create large supercells. Tornadoes can occur everywhere in the world, from Spain to Wales and from Japan to the USA. But they mostly occur in the United States. • All year long. But most come during the months of April, May, and June. The fewest are in December and January. About four out of every five tornadoes form in the afternoon or evening. The worst time is between four o’clock and six o’clock in the afternoon. Tornadoes strike all over the world. But the United States holds the record-an average of 700 a year. Texas leads the other states with about 115 tornadoes a year. But in 1967, Texas outdid itself with 232 twisters! • Because they are filled with dirt. Tornado winds suck up everything they touch. Tornado came from the Spanish words • “Tronado” meaning thunderstorm • “Torrar” meaning to turn. What is the difference between watches and warnings? •A tornado watch means conditions are right for tornadoes to form, you should be alert. •A tornado warning means a tornado has actually been spotted. You should be ready to take shelter-immediately. • Stay calm! • Look for safe shelter like a basement, small closet or bathroom. • Stay away from windows, the broken glass can cause injuries. •Listen for reports on a portable radio. •Keep a weather radio with batteries if you live in an area with lots of tornadoes. •Protect your body with a mattress or blankets •Evacuate mobile homes and find shelter in a solid structure. •If you are out in the open, find a ditch or overpass to hide in. For more information, contact your local Red Cross chapter, National Weather Service office, or emergency management agency. You can also visit the Web sites: American Red Cross http://www.redcross.org/ National Weather Service http://www.nws.noaa.gov/ Federal Emergency Management Agency http://www.fema.gov/ Related sites: http://www.fema.gov/kids/twins/tornado/tornado1.htm http://www.nationalgeographic.com/forcesofnature/ http://www.nationalgeographic.com/eye/tornadoes/tornadoes.html http://www.ncdc.noaa.gov/oa/climate/severeweather/extremes.html http://www.redcross.org/disaster/safety/tornados.html http://www.stemnet.nf.ca/CITE/naturaldisasters.htm