Why Is the Radar Sometimes Wrong?

Doppler Radar is a valuable tool that meteorologists frequently use to look inside a storm and forecast the weather.

A weather radar follows some of the same principles at a flashlight. While a flashlight uses rays of light to detect objects in the dark, radars detect objects in the atmosphere using pulses of energy.

Weather radars work as both transmitters and receivers. A weather radar sends out a microwave beam then listens for echoes that bounce back from all sorts of precipitation types and intensities.

The radar then measures how much of the beam bounces back and exactly how long it takes to return. The amount of energy reflected back to the radar is proportional to the precipitation intensity.

One common feedback problem of radars is ground clutter. In this case, the radar is picking up a scattering of objects on and near the Earth's surface. It is most common when the radar is tilted at a lower level.

The radar doesn't pick up only rain, sleet, snow and hail but can also pick up and represent bugs, insects, dust and even bats!

Another common problem with Doppler Radar is how it handles precipitation that evaporates before it reaches the ground. This virga is detected by radar as normal rainfall.

To depict what is real and false correctly in this situation, be sure to use multiple radar sites and view the precipitation at different heights.

More Weather Glossary

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    After a cold, clear winter night without much wind, the ground and nearby tree branches may be covered by tiny, white ice crystals.

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This Day In Weather History

New Holstein, WI (2007)
Strong thunderstorm winds blew two airplanes into one another at the local airport.

New York/MA (1819)
Two simultaneous cloudbursts, 45 miles apart; A bucket survey claimed 15" of rain fell at Catskill, NY. Highways were completely washed out. One washout started west of the old Albany Post Road and spread eastward across the road until it was 190 feet wide and 80 feet deep in a distance of 160 paces. At Westfield Valley, "suddenly the windows of heaven seemed to have been opened and the rain fell in such torrents that in less than 5 hours, Westfield River rose at least 20 feet above its usual height at low water. The river overflowed its banks with great rapidity and violence, sweeping away every bridge, fence and building which opposed its current."

Pittsburgh, PA (1872)
Cloudburst of 30 minutes followed by a flash flood. Over 133 people drowned on the north side of Butcher Run and Wood's Run.

Rough Weather