To understand the Doppler radar you first need to know about the Doppler Effect. The Doppler Effect (or Doppler shift) is named after Austrian physicist Christian Doppler. Doppler observed that the frequency of light and sound waves was affected by the relative motion of the source and the detector. To explain this further here's an example - when a vehicle sounding a siren approaches, passes and goes away from an observer, the sound heard gradually increases during the approach, is identical at the instant of passing by and then decreases during the moving away. A Doppler radar uses the Doppler Effect to measure variations in sound and interpret the information thereafter. The Doppler radar is helpful in the sense that it is able to identify actual cloud formations and precipitation levels. Based on these observations weather officials can make their forecast.