An Observational Analysis of a Developing Mesoscale Convective Complex

Abstract

Dual-Doppler radar, surface mesonet, satellite, and upper-air sounding data from the 1985 Preliminary Regional Experiment for STORM-Central field experiment are used to analyze the early growth stages of a mesoscale convective complex (MCC) that developed in the network on 3 June 1985. This MCC was characterized by a complex distribution of convective clusters and intervening stratiform echo as it grew from its initial stage to the typical meso-α-scale cloud shield structure at its mature stage. The MCC exhibited two very different states of organization as it grew. The early state was characterized by a relatively weak and disorganized surface pressure pattern and a highly variable three-dimensional mesoscale flow structure. The later state was characterized by a well-developed mesohigh-wake-low surface pressure pattern and more organized mososcale flow fields. The evolution between these two regimes occurred about 1 h after the upper-level cloud shield reached MCC proportions and manifested itself as a rapid, almost discrete transition that took place over a period of about 30 win. The flow structure in this system was highly complex compared to the two-dimensional squall-line conceptual model. Five separate flow branches coexisted and interacted with one another throughout the observed development of the MCC, and the structure of some of them changed considerably as the system evolved. Notably, the rear inflow evolved from a highly variable westerly flow that ascended in its northern half and descended in the south, to a more uniformly descending rear-inflow jet. This transition was dynamically linked to the development of an upper-tropospheric mesohigh, which we hypothesize blocked the upper-trapospheric flow and partially forced the descent of the rear inflow.