Overview of Weather Radars » Reflectivity Scales
Typical values of radar reflectivity factors for non-precipitating clouds or light drizzle would range from 10-5 to 10; for very heavy rain and hail the factor would be as high as 107. Because these values range over several orders of magnitude and are difficult to depict graphically in much detail, radar products typically use an easier-to-interpret logarithmic scale of dBZ (decibels of Z).
The scales usually span from -28 to +28 for clear air mode and 0 to 75 for precipitation mode.
In precipitation mode, low dBZ values (blue and green colors) indicate light precipitation, while higher values in the yellow, orange, and red colors mean heavier precipitation. Values above about 45 dBZ signify intense precipitation and are nearly always caused by thunderstorms. Anything above 60 dBZ generally means that the sample volume contains some hail.
