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Small developing shower clouds were studied from a Caribbean island using visual and radar techniques. Within as little as 25 minutes of the formation of a cloud, precipitation had developed in its summits to an estimated diameter of ½ mm. The subsequent growth of these particles, giving rise to an intensification of radar reflectivity at the rate of an order of magnitude per 60 to 200 seconds is shown to be consistent with growth by gravitational coalescence. In small clouds (tops between 3 and 5 km) the peak reflectivity factor attained in a shower increases rapidly with the height of its summits but in clouds that extend above the freezing level the peak reflectivity factor does not exceed a value of about 3×105 mm6/m3.
Peter M. Saunders (Mon,) studied this question.