AN OBSERVATIONAL ANALYSIS OF A DEVELOPING MESOSCALE CONVECTIVE COMPLEX

Dual-Doppler radar, surface mesonet, gatellite, 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 meso scale convective complex (MCC) that developed in the network on 3 June 1985. This MCC was characterized by a complex distribution of convect ive clusters and intervening stratiform echo as it grew from its initi al stage to the typical meso-a-scale cloud shield structure at its mat ure stage. The MCC exhibited two very different states of organization as it grew. The early state was characterized by a relatively weak an d disorganized surface pressure pattern and a highly variable three-di mensional mesoscale flow structure. The later state was characterized by a well-developed mesohigh-wake-low surface pressure pattern and mor e organized mesoscale flow fields. The evolution between these two reg imes occurred about 1 h after the upper-level cloud shield reached MCC proportions and manifested itself as a rapid, almost discrete transit ion that took place over a period of about 30 min. The flow structure in this system was highly complex compared to the two-dimensional squa ll-line conceptual model. Five separate flow branches coexisted and in teracted with one another throughout the observed development of the M CC, and the structure of some of them changed considerably as the syst em evolved. Notably, the rear inflow evolved from a highly variable we sterly flow that ascended in its northern half and descended in the so uth, to a more uniformly descending rear-inflow jet. This transition w as dynamically linked to the development of an upper-tropospheric meso high, which we hypothesize blocked the upper-tropospheric flow and par tially forced the descent of the rear inflow.