Abstract
Observations from the Oklahoma-Kansas Preliminary Regional Experiment for STORM-CENTRAL (OK PRE-STORM) have been used to study the evolution and propagation characteristics of a long-lived (≥16 h) mesoscale convective system (MCS) that produced locally heavy (50–100 mm) rainfall during 26–27 June 1985. The MCS formed in association with a synoptic-scale cold front and upper-level trough system. Mesoscale ascent contributed to an increase in convective available potential energy (CAPE) and a decrease in convective inhibition, facilitating the development of deep convection.
During the late morning and early afternoon hours convection was present along and within an ∼200-km zone in advance of the cold front. In advance of the main precipitation area, a series of nearly parallel rainbands formed from in situ boundary-layer cloud streets. The development and organization of these rainbands was aided by the moderate-to-large CAPE, small convective inhibition, and moderate unidirectional shear at low levels that characterized the preconvective environment over the ∼200-km region ahead of the cold front. The discrete eastward progression of convection afforded by the formation of the rainbands in advance of the main precipitation area represents a distinct departure from the propagation characteristics of many previously observed cases and idealized simulations of linearly oriented MCSs, where system propagation depends crucially on periodic regeneration of multicell convection along a storm-induced cold pool.
The MCS weakened over southern Kansas after the merger of the main precipitation area with the quasi-stationary presquall rainbands. During its dissipating stages, it exhibited circulation and surface pressure features commonly reported during the mature-to-decaying stages of previously observed systems. These features included a surface mesohigh to the rear of the leading edge of the precipitation, and regions of mesoscale ascent and subsidence associated with a trailing anvil and a sloping rear inflow jet. The presence of these features, despite a system evolution and precursor environment different from those of a more classical linearly oriented MCS supports the consensus from earlier studies that internal processes such as spatial variations in diabatic heating are likely responsible for the observed mesoscale flows in the mature-to-decaying stages of large MCSs.
