Clouds play a vital role in climate by virtue of their ability to transform radiant energy and the phases of water substance in the atmosphere. But they have been received disproportionately little consideration in hydrologic cycle studies, partly because it has been difficult to observe them in a quantitative manner. The rapid development of millimeter-wavelength cloud radars in the last decade now allows unprecedented observations of the structure and composition of clouds from the ground, from research aircraft, and (soon) from space. This article will describe the operating characteristics and scientific capabilities of one of the world's finest cloud radars. NOAA/ETL's transportable, ground-based cloud radar has been used in numerous field experiments to observe the macrophysical and microphysical features of nearby clouds. This Ka-band (8-mm-wavelength) radar has Doppler, polarization-diversity and full scanning capabilities. The scanning polarization data are used to identify and distinguish regions of cloud populated dominantly by water droplets, planar crystals, columnar crystals, and other ice particle types. In combination with simultaneous measurements from radiometers, data from this radar are used to retrieve the vertical profiles of hydrometeor median size, total concentration, and mass content for ice clouds and liquid water clouds. Although severely attenuated by moderate and heavier rainfall, the radar provides excellent high-resolution observations of any snowfall intensity and is well suited for detailed studies of snowstorms over small watersheds, including mountain and urban basins.