What Is A Tornado? A tornado is a column of air, which rotates violently and is in contact with the ground and a cumulonimbus cloud. Formation Of Tornadoes There are three main things needed to form a tornado. The first one is a layer of warm, humid air near the ground and strong south winds. There's colder air in the upper atmosphere with strong west or southwest winds. The sir close to the surface is not nearly as dense as the cold, dry air above. This is known as instability. If the warm, moist air is given a push upwards, then the air will distribute moisture and energy to form a thunderstorm which may be the parent of a tornado. The second thing needed to form a tornado is a wind shear, which is a change in wind speed and direction due to height. This is connected to the development of rotation, that a tornado may form. The final thing needed is hot, dry air between the upper and lower layers. This air allows the warm air below it to increase its warmth and cause the atmosphere to decrease in stability. Signs Of A Tornado - Dark, green colored sky - Wall Cloud - Big Hail - Loud roaring, like that of a freight train Sample Heading 4 This is where you tell your story or provide information to your visitors. Be sure to include changes or new information in a timely fashion. By keeping your Web site up to date, visitors will have a reason to return often. You may add text or HTML code to this field and make it as complex as you want. Or, you may erase the content of this field causing it to be hidden when people visit your site.