<p>Radar is another major tool of weather observation and forecasting. It is used primarily to observe clouds and rain locally. One type of radar, called Doppler radar, is used at weather stations throughout the world. Doppler radar measures changes in wind speed and direction. It provides information within a radius of about 230 kilometers (143 miles). Conventional radar can only show existing clouds and precipitation. With Doppler radar, meteorologists are able to forecast when and where severe thunderstorms and tornadoes are developing.</p>

<p>Doppler radar has made air travel safer. It lets air traffic controllers detect severe local conditions, such as microbursts. Microbursts are powerful winds that originate in thunderstorms. They are among the most dangerous weather phenomena a pilot can encounter. If an aircraft attempts to land or take off through a microburst, the suddenly changing wind conditions can cause the craft to lose lift and crash. In the United States alone, airline crashes because of microbursts have caused more than 600 deaths since 1964.</p>