What is a tornado??
A tornado is rapidly spinning air that develops from a thunderstorms and is on the ground. The ingredients for a tornado are a thunderstorm, winds changing speeds with height and rapidly rising air. When you watch a thunderstorm develop you will notice that the clouds build upward. This rising air is what causes all the rain and hail to form from the water in the air. The addition of changing wind speed and direction with height causes the rising air to spin. Most thunderstorms do not produce tornadoes because the spin is not balanced with the air rising from the surface. When the balance is just right though between the rising air coming into a thunderstorm and the winds changing with height then a tornado can form. Tornadoes can be weak or strong and last a few seconds up to many minutes.
How are tornadoes formed??
Tornado conditions are caused when different temperatures and humidity meet to form thunderclouds. In the United States, warm, wet winds from the Gulf of Mexico move northward in spring and summer, meeting colder, dry Canadian winds moving southward. The place where these two winds meet is called a dry line. High, dry air coming from the north piles on top of low-moving, moist Gulf air at a height of over 10,000 feet. The warm southern winds try to rise, but the cold northern air blocks them. This clash causes the warm, trapped air to rotate horizontally between the two air masses. At the same time, the sun heats the earth below, warming more air that continues to try and rise. Finally, the rising warm wind become strong enough to force itself up through the colder air layer.
When this occurs, the cold air on top begins to sink, sending the rising warm wind spinning upward. The warm winds rotate faster and faster in a high column. When the updraft is strong, the column can rise to heights of 10 miles or more, twisting at speeds of up to 100 miles an hour. The rotating winds produce strong storm clouds about 70,000 feet high, sometimes spreading 10 miles wide.
This storm system may stay intact for several hours, at which point its thunderclouds are known as super-cells. These storm clouds can send down an inch of rain in a mere ten minutes or shower the ground with baseball-sized hailstones. Super-cells can accumulate into huge clusters, forming a line almost 100 miles long, which can then develop into mesocyclones.