Weather radars use a variety of color schemes to indicate different types and intensities of precipitation. Greens indicate light to moderate rain, while reds and purples indicate heavy rain or hail. Whites or blues are snowfall and pink indicates freezing rain, sleet, or a wintry mix.
The colors used on a radar reflectivity image are based on a combination of surface observations and computer model estimates of vertical temperature structure within the areas where the radar echoes are detected. The exact locations of snow/ice/rain boundaries are often not accurate, but are reasonable approximations based on the combination of observations and model outputs.
The most common occurrence on radar reflectivity images is what is called "ground clutter." Echoes from objects like buildings and hills generally appear within a radius of about 25 miles of the radar as roughly circular regions with varying echo intensity. These echoes can be removed by using mathematical algorithms called "ground clutter removal" techniques, but not all echoes are completely eliminated.
Velocity imagery also uses red and green colors to show the radial velocities of winds blowing away from the radar (red) or toward it (green). Winds flowing in one direction are shown with darker reds or purples, while wind flows moving in the other direction are usually depicted as lighter greens or blues.
Doppler radars measure "reflectivity" (dBZ) and "radial velocity" (m/s) in many cells around the radar station. The reflectivity values represent the strength of returned energy to the radar, while radial velocities are used to estimate rainfall rates and tornadoes. The reflectivity and radial velocity values can also be displayed together in a single image called a "reflectivity map."
