ABOUT EL NINO: El Nino is a cyclical warming of the ocean waters in the central and eastern tropical Pacific that generally occurs every three to seven years, usually around the holidays. It is associated with changes in air pressure and the movement of high-level winds, and can affect weather worldwide. In the United States, En Nino normally results in warmer-than-normal temperatures across the northern and western states. Wetter conditions result in the south, with dry weather across the Ohio Valley and Pacific Northwest. El Nino typically peaks during the winter months. It alternates with La Nina, the cooling of ocean waters in the same region of the Pacific.
HOW TORNADOES FORM: Air is a gas and water is a liquid, but in the realm of science, both fall into the category of fluids. When a fluid's flow is disturbed, it causes turbulence. For instance, branches sticking into the water can disrupt the flow of a stream, forming tiny eddies or whirlpools. The same thing happens when you move your hand quickly through water. Technically, these are known as vortices. The water moves in a circular motion around a central point, and this causes a depression or cavity to form in the center, which draws flowing objects towards that center. Think of water spinning down the bathroom drain.
These sorts of swirling vortices can also form in air. As a thunderstorm develops, if the wind speeds up and changes direction, this can cause a horizontal spinning effect in the lower atmosphere. As air rises, pulled upwards by the developing thunderstorm, it tilts the horizontal rotation into a vertical rotation. A tornado is simply a violently rotating column of air that extends from a thunderstorm in the atmosphere to the ground. The pressure inside can be 10 percent lower than the surrounding air, and this causes that air to rush towards the low-pressure center from all directions. As it streams inward, the air spirals upward around the core until it merges with the airflow of the thunderstorm that gave rise to the tornado.
The American Meteorological Society and the American Geophysical Union contributed to the information contained in the TV portion of this report.