Base radial velocity images provide information about wind speed and direction. These are determined by whether a target is moving toward or away from the radar along a radial direction. In this example, warm colors (reds) indicate motions away from the radar and cool colors (greens) represent motion toward the radar. Targets that are stationary or moving perpendicular to the radar beam have no radial velocity and are colored gray.

These are the most common radar products and the ones we will focus on in this module. Other radar products, such as storm total precipitation and storm relative velocity, are also quite useful and may be explored here:
http://www.srh.noaa.gov/jetstream/doppler/baserefl.htm