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Doppler Radar
Doppler radar, developed by Christian Doppler, uses sound waves to detect weather occurrences. Doppler was an Austrian scientist who proposed the principle behind today's radar. In 1842, he said that if the source of a sound was moving, the pitch of the sound would change. In modern radar this means that an antenna sends out radio waves reflected by objects in the air. Scientists use Doppler radar to learn about a tornado's structure and whether winds in an area are strong enough to produce a tornado. This helps scientists determine whether to release tornado warnings for general areas.
Weather Conditions
Predicting tornados is half art and half science. Though tornado predictions involve some guesswork, they are based on weather conditions. These conditions are reported by computer to the U.S. Storm Prediction Center. Scientists look at colliding weather fronts and strong thunderstorms that could produce the most destructive type of tornado, the supercell. The four principal conditions considered by scientists are: moisture, lift, wind shear and instability. These are the aspects of temperature and wind flow that create tornado conditions.
Cloud Formation
Tornadoes form from cumuliform clouds under conditions of powerful convection---the transfer of heat by the movement of a heated substance from one position to another. This occurs when cold and warm fronts meet, fueling the growing storm. When forecasters see the right clouds in combination with the appropriate temperatures and winds, they know the chance of a tornado forming is high.
Basic Tools
Though computers put all the data together for quick analysis, the basic tools scientists use to predict tornadoes are simple ones long used to track weather. Barometers measure air pressure, thermometers measure temperature, hygrometers measure relative humidity, wind anemometers measure wind speed and direction and ceilometers measure cloud height and visibility. Along with satellite images of the Earth and its weather, scientists use these simple tools to make weather predictions. On a large scale, these instruments in weather centers across the nation provide the information used by National Weather Service meteorologists.
Human Intelligence
While computers can do the statistical analysis and gather data, humans put the pieces of the tornado puzzle together and decide whether a warning should be issued. Scientists have a difficult time predicting tornadoes one or two days in advance because conditions can dramatically change in a short period of time. Predicting these events requires scientists to analyze data given by computers, monitor weather conditions, and decide whether the weather center will notify residents of a possible storm.