The Nexrad Radar Coded Message (RCM) product originates as an automated
text message generated at each NWS radar site. The RCM is edited by an automated process
that checks for meteorological validity when compared to current satellite images,
synoptic conditions, neighboring radar sites, and lightning.
The colors are the different echo intensities (reflectivity) measured in dBZ
(decibels of Z). "Reflectivity" is the amount of transmitted power returned to the radar
receiver. Reflectivity (designated by the letter Z) covers a wide range of signals (from
very weak to very strong). So a more convenient number for calculations and comparison,
a decibel (or logarithmic) scale (dBZ), is used. The dBZ values increase as the strength
of the signal returned to the radar increases.