Thunderstorms can form quickly and are not always easy to predict. So this is why engineers create Doppler radar stations that are able to detect approaching thunderstorms. Doppler radar works by sending out pulses or radio waves, then measuring how long it takes the waves to bounce off objects and return. In the case of thunderstorms, the radio waves bounce off the rain or hail. Information from the radar station can determine the size of a storm, how fast it is moving, which direction it is moving, and whether or not there is danger of a tornado. Because tornadoes usually occur in flat areas, such as grasslands, radar stations are often placed in these areas.