Dear Tom,
What does dBZ stand for when it is used on the radar charts?
Leo Peters
Dear Leo,
The label dBZ stands for decibels (dB) of reflectivity (Z) and provides the radar user with a scale to evaluate the strength of the echo returns. The dBZ values increase logarithmically as the strength of the returned radar signal increases. National Weather Service Doppler radars can measure reflectivity values as low as 28dBZ and as high as 75 dBZ. The 20 dBZ level is typically considered the lowest reflectivity level for precipitation, with values less than that indicating a non-precipitation return. Normally, high dBZ values relate to intense rainfall rates. Hail, an excellent reflector, also yields very high dBZ values, so echoes producing high dBZ numbers often indicate thunderstorms producing hail or heavy rainfall.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
