Each convective shower has an updraft where warm moist air rises up. The rising air cools and the moisture condenses out forming cloud droplets and eventually rain.
Rain falls in the down draft.
The area of falling rain may be small. The rain generally does not fall in the updraft portion and there may be a sharp cutoff from no rain to rain. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.