Do clouds reflect radio waves? Specifically, those waves used in radars. And, what kind of matter refracts or reflects radio waves?
It is possible to select the operating frequency for a radar set to get a good return off a wet cloud. In fact, radars of this type are sensitive to the amount of water in the cloud and are used to map out the intensity of rainfall inside the cloud bank. The snazzy color-coded precipitation maps you see on weather programs are generated this way.
Radio waves are reflected off of objects that are electrically conductive and bent when passing through space which contains ionized gas. The amount of reflection or refraction is sensitively dependent on the wavelength of the radio waves and the angle of incidence between the wave and the object. More details can be had by consulting the amateur radio stack exchange.