Scientific studies measure the proportion of cloud condensate that precipitates out as rain using the metric of precipitation efficiency (PE), which varies systematically by storm type and atmospheric conditions.
The claim states that a predictable proportion of a cloud precipitates out as rain during a storm. This is a specific, empirical meteorological concept known as precipitation efficiency (PE), which is studied extensively in the literature to quantify the fraction of cloud condensate or water vapor converted into surface precipitation. Papers 0, 1, and 11 explicitly examine precipitation efficiency and confirm that this proportion can be modeled, categorized by storm type, and analyzed systematically. Therefore, the claim is supported.