Have you ever seen a television weather caster show a colored map of where rain or snow is falling? The colors that you see indicate where the precipitation is and how heavy it is. So, how does he/she get this information? The precipitation is detected by one or more of the National Weather Service’s 150 weather radars, processed by computers and made available to weathermen around the world.
So, what is radar and how does it work? RADAR is an acronym for RAdio Detection And Ranging and was developed more than 100 years ago when countries around the world realized radio waves could be used to detect objects that the human eye couldn’t see. Now, weather radars are used to help meteorologists see raindrops, snowflakes, hail and other small objects in the atmosphere.
Weather radars send out a burst of radio waves from a large dish inside the radar dome. The radar dome looks like a large ball on top of a tower. The radio waves travel through the air until they hit something in the atmosphere. When they hit an object, some of the radio waves bounce off the object and travel back toward the radar. The radar listens for these reflected radio waves, something that is called a radar “echo.”
From the echo, the radar figures out how much energy (radio waves) is returned to the radar, as well as how long it took to return. Using this information, the radar estimates how heavy the precipitation is and how far away it is. As the radar’s dish spins around inside the dome, it sends out hundreds of bursts of energy each second and collects information on the reflected energy. One full scan of the atmosphere takes around five minutes to complete.
Weather radars also employ Doppler technology (that’s why weather radars are often called Doppler radars). Doppler technology allows the radar to determine whether the individual rain droplets or snowflakes are moving toward or away from the radar, which then allows the radar to estimate the winds in a storm. Meteorologists use this wind information to help warn people of gusty winds from a thunderstorm or to detect rotation in the atmosphere that could lead to the formation of a tornado.
Ideally, the weather radars would detect only rain, snow or other precipitation, but objects like birds, insects and even passing traffic on a nearby highway can reflect energy back to the radar. Fortunately, recent improvements to weather radars now allow meteorologists to better understand what the radar is seeing. Meteorologists can determine whether the precipitation is rain, snow, sleet or hail. By knowing the type of precipitation and how heavy it is, the radar can also make estimates of how much rain or snow has fallen.
Radar is truly one of the most valuable tools a meteorologist can use. In the summer, it is the best tool for watching for developing thunderstorms, tornadoes, strong winds and heavy rain and is used to issue warnings for dangerous storms. In the winter, the radar can be used to monitor winter storms and see snow, sleet and rain.
