why does the WSR-88D imagery sometimes show radar echoes on clear days?
The WSR-88D operates in one of two modes, clear air, or precipitation. The legend on the right side of the image indicates the active operating mode, as shown below: Generally speaking when there is no precipitation within the range of the radar site (230 Km, or about 140 miles), the radar system can be switched into “clear air” mode. In clear air mode the sensitivity of the radar is increased dramatically. The WSR-88D can actually detect energy levels so small they are reported in terms of negative values ( i.e. -10 DBZ). This enables the radar to detect boundaries between air masses, temperature inversions in the atmosphere (warm air above cooler air), and non meteorological phenomena such as smoke plumes, and more. So when you look out your window and see fair skies, yet the WSR-88D image is showing echoes over you, it generally means one of two things. First, check to see which mode the radar site is operating in. If it is in clear air mode the echoes on the image are simply indica
