A tornado is a violently rotating column of air that comes in contact with the ground. A tornado, which forms from a cumulonimbus cloud, is almost always observable as a "funnel cloud." Although there have been some instances in which the "funnel cloud" is not observable. Tornadoes usually develop in thunderstorms that develop in warm, moist air in advance of eastward-moving cold fronts. The tornadoes that occur in winter in early spring are usually associated with strong frontal systems that form in Central Untied States and move east.

Before a thunderstorm even develops, wind direction changes and wind speed increases with increasing height. This gives off an invisible, horizontal spinning effect in the lower atmosphere. In the storm updraft, rising air tilts the rotating air from horizontal to vertical. The area of rotation that occurs is 2-6 miles wide. This area is rain-free and most of the strong...