Those Terrible Twisters

Thunderstorms are generated when warm, moist air is lifted up through the atmosphere and then expands, colls and finally condenses into tiny cloud droplets of water and ice. The lifting process is many times caused by what is called convection, which is a transfer of energy from the lower levels of teh atmosphere to the upper regions. Convection begins when the heated surface of the earth warms the lower atmosphere, causing the heated air to become warmer than the surrounding air. As the heated air rises, it expands and cool, and finally the water vapor changes or condenses into tiny bits of liquid water or ice. When condensastion takes place, heat is released which warms the parcel of air even more, causing it to riseeven higher in the atmosphere. During this process, all air motion is upward and is the first stage of thunderstorm development.