Reflectivity is the amount of transmitted power returned to the radar receiver, measured in dBZ (decibels of Z, where Z represents energy). Base reflectivity measures reflectivity from the radar antenna's lowest "tilt" angle (0.5° above the horizon). In contrast, composite reflectivity records the highest reflected energy found across multiple elevation angles measured by the radar antenna.
A value of 20 dBZ is typically the point at which light rain begins while values in the range of 60-65 dBZ could be an indication of hail or other severe weather.
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