Observations of rainfall from warm clouds

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Abstract
Rainfall from non‐freezing clouds has been widely reported but detailed observations are sparse. During June 1952, ten days of observations were made during trade‐wind weather conditions on the island of Oahu. Rainfall was observed during each of the 10 days, and in no instance did cloud temperatures below 7°C occur. Aircraft were used to obtain temperature and humidity soundings supplementary to the Honolulu radiosonde and to measure the dimensions of the clouds. Raindrop sizes were recorded on a continuously moving dye‐treated paper tape at two locations. Data on rainfall were obtained from 5 recording raingauges on the crest of the Koolau Mountain Range and from 32 standard raingauges in an area of 130 m2 Pilot‐balloon ascents were made daily on the windward coast of Oahu to supplement the Honolulu Weather Bureau wind data. A continuous record of cloud conditions and motions was made by lapse‐time motion‐picture photography and supplemented with photographs from aircraft.Rainfall intensities exceeding 3 mm/hr were observed from clouds with bases at 2,000 ft (18.6°C) and tops at 7,500 ft (10.2°C). Raindrop sizes as large as 2 mm in diameter were observed from clouds 6,000 ft deep. Light‐intensity rains from small cumulus clouds frequently consisted of raindrops which were relatively large (2 mm diameter) but low in number.

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