Weather Radars. The presence of heavy rain and hailstones in cumulo-nimbus clouds is a natural phenomenon which is of vital importance to people who fly in aircraft. With a suitable radar fitted in the nose of an aircraft, this precipitation can be detected and the information presented to the pilot so that he can steer the aircraft to avoid the dangerous turbulent conditions associated with cumulo-nimbus clouds. This is, of course, the basis of weather radars which have been used for many years, and are now regarded as more or less essential for civil aircraft.