One scale (far left) represents dBZ values when the radar is in clear air mode (dBZ values from -28 to +28). Each reflectivity image you see includes one of two color scales. The dBZ values increase as the strength of the signal returned to the radar increases.
So, a more convenient number for calculations and comparison, a decibel (or logarithmic) scale (dBZ), is used. Reflectivity (designated by the letter Z) covers a wide range of signals (from very weak to very strong). 'Reflectivity' is the amount of transmitted power returned to the radar receiver.
The colors are the different echo intensities (reflectivity) measured in dBZ (decibels of Z) during each elevation scan.
