ABOUT TORNADOES: A tornado begins with a thunderstorm cloud, which can build up a lot of energy. If this energy creates a particularly strong updraft of air, it will form a vortex, much like how a whirlpool forms in a draining bathtub. The air is pulled toward the center in a spiral, forming a tornado under the thundercloud. Wind speeds can reach 200 to 300 MPH, and if the dangling vortex touches ground, the combination of the whirling wind's speed, the updraft, and pressure differences can cause severe damage. The path of a tornado is determined by the path of the parent thundercloud, but it will often appear to hop (called a "jumper"). This occurs when the vortex is disturbed, causing it to collapse momentarily and reform.
HOW A DROUGHT COMES ABOUT: Drought doesn't have a single cause; rather, it happens as several contributing factors converge all at once. But the most immediate cause is high atmospheric pressure. When the air sinks, producing high pressure, this keeps clouds from forming, so there is less humidity and therefore less rainfall. This is often seasonal in many regions of the world, but the Sahara and Kalahari deserts in Africa, and Asia's Gobi desert, for example, experience high pressure for most of the year. How long a drought lasts depends on how the air and sea interact to transfer moisture to the air, and how much moisture the soil retains in a given region, among other factors.
The American Meteorological Society and the American Geophysical Union contributed to the information contained in the TV portion of this report.