Updraft Measurements Beneath the Base of Cumulus and Cumulonimbus Clouds

Abstract

During the summers of 1964 and 1965, the Colorado State University Hail Suppression Research Project made updraft measurements beneath the base of cumulus and cumulonimbus clouds in northeastern Colorado. Analysis of the data reveals that the average maximum updraft appears to be located in the right-front quadrant of the radar echo. For heavily precipitating cumulonimbus clouds, this average maximum updraft exceeded 6 m sec⁻¹. There is also a proportional increase in the magnitude of the updrafts relative to the amount of precipitation falling from the cloud. Average updrafts of all measurements on moderately and heavily precipitating cumulonimbi were 2.5 m sec⁻¹ and 3.8 m sec⁻¹, respectively. Much stronger updrafts can be expected on the common boundaries of converging cumulonimbus clouds. Updrafts appear to exhibit laminar flow characteristics with turbulence found upon entering and leaving the strong updraft regions. Smooth steady updrafts may exist for an hour or more, indicating that the more intense thunderstorms possess a steady-state phase. During this steady-state phase, areas of scud cloud were normally found in the areas of strongest updrafts. From a limited study, no apparent correlations were found between maximum updrafts observed and certain environmental parameters.