Tornadoes
Uploaded by therat420 on Mar 03, 2000
A tornado is a violently rotating column of air that extends from a thunderstorm cloud to the earth’s surface. They are sometimes nicknamed twisters because of their shape and because of what they do. The winds in the tornadoes are usually 100mph or less. In +F4's they can exceed 250mph. They usually stay on a track of a few miles or less and are less than 100 yds. wide. For the development of tornadoes there are a few conditions required. An abundant low-level of moisture and unstable atmosphere is required not only for the tornado, but for a thunderstorm also. A “trigger”, which is a cold front or low level zone of converging winds, is needed to lift the moisture and the air. When the air rises , it becomes saturated and continue to rise higher and higher. They then form in areas where winds at all levels of the atmosphere are strong and turn clockwise with height.Some tornadoes appear as a funnel shape and some have a churning smoky look . Some contain multiple vortices , which are small individual tornadoes rotating around a common center. Some can be invisible , with only swirling dust or debris at ground level as the only indication of the tornado’s presence. Tornadoes can occur at any time of the year, and anywhere in the world. The unique geography of the US is what helps us produce some of the most violent tornadoes because of the favorable condition’s for their development . The months with the greatest amount of tornadoes are April, May and June . Tornado seasons vary in different parts of the US. In the Southeast the peak season is February through April. In the northern plains it is June through August. Tornado frequency is high in the South during late winter and in the Plains, mid-west, and Ohio Valley it is high during early spring through summer. They can occur at any time of day but are more likely to occur 2-7pm. The most tornadoes occur at around 5pm. In Tornado Alley, very few tornadoes occur in the morning . In the southeast , most of the tornadoes occur during the night and early morning hours. Most tornadoes form in conjunction with thunderstorms. Forecasters therefore have to determine which areas are most at risk with severe thunderstorms. It is very difficult to tell the difference between a severe thunderstorm with...