Precipitation production in three Alberta Thunderstorms

Radar reflectivity patterns of three large, long‐lasting Alberta thunderstorms were analysed to determine the precipitation content and the outflow rate as functions of time. These quantities were then used to calculate the rate at which precipitation is generated and the characteristic time of the precipitation process, as functions of time. The maximum hourly‐average precipitation content was approximately 0.5 Tg for one storm (Storm A) and 1 Tgfor each of the other two. The maximum hourly‐average outflow rate was approximately 0.5 Gg s−1 for Storm A and 0.8 Gg s−1 for the others. Each storm had two fairly well defined periods of peak precipitation production lasting about half an hour and separated by about 45 min. The characteristic time, defined as the ratio of the instantaneous precipitation content to the outflow rate, was somewhat longer on the average for one storm than for the other two, but in no case was far from 20 min, which is approximately the time required for rain to develop in cumulonimbus clouds. The total amounts of rain produced by the three storms ranged from 4 to 7 Tg.