An integral part of the WSR-88D program is the development of a data processing and distribution network. The letters refer to archaic military designations of the different frequency or wavelength 'bands' that these radars operate in. They harken back to the early development of radar in WWII and somehow have stuck with us. Mostly used for clear-air turbulence studies. Not easily attenuated but require large dishes and motors.
Portability means they're often used in research field programs.
Nearby bands are often used for microwave communications links. However, attenuated rapidly as they pass through storms. Share some space with police speed radar. Actually two bands, split down the middle by a strong water vapor absorption line. Similar comments as with X-bands, above.