Downdrafts within High Plains cumulonimbi. I - General kinematic structure

Abstract This paper presents results from a comprehensive investigation in which observations from several case studies an integrated with three-dimensional cloud model results to examine the general kinematic structure of downdrafts associated with High Plains precipitating convection. One particular downdraft type, the low-level precipitation-associated downdraft, is the focus of this paper. General airflow and trajectory patterns within low-level downdrafts are convergent from 0.8 km upwards to downdraft top, typically less than 5 km AGL. Observed mass flux profiles often increase rapidly with height as a result of strong buoyancy forcing below the melting level. Inflow to the low-level downdraft although vertically continuous, can be separated into two branches. The up-down branch originating within the planetary boundary layer initially rises up to 4 km and then descends within the main precipitation-associated downdraft. The midlevel branch, usually more pronounced during early downdraft stages, ori...