Heavy Rainfall from very Shallow Convective Clouds

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Abstract
A heavy rainfall from very shallow convective clouds is studied. We pay attention to the causes of large condensation rate and of high precipitation efficiency which seem to be necessary for the occurrence of heavy rain from very shallow clouds. Synoptic features are as follows: 1) A weak tropical depression was nearly stationary over the sea to the southwest of the heavy rain areas. 2) Warm and moist air was observed below inversion layers in the eastern part of the depression. 3) Stratification in the lower troposphere was latently unstable. Distributions of rainfall amount seem to be strongly afected by mountain ranges. A narrow and straight echo band which might be composed of crowded cumuli repeatedly appeared over the area on the windward side of a mountain range. Precipitation efficiency for a heavy rain area was very high, if we assume from the results of analyses that the airflow below 900mb was blocked by the mountain range and ascended penetratively up to 650mb. Crowded maritime cumuli and very moist air observed around the heavy rain area might be favorable for the high precipitation efficiency.

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