The Simulated Structure and Evolution of a Quasi-Idealized Warm Season Convective System with a Training Convective Line

This study details the development and use of an idealized modeling framework to simulate a quasi-stationary heavy-rain-producing mesoscale convective system (MCS). A 36-hour composite progression of atmospheric fields computed from 26 observed warm-season heavy-rain-producing training line/adjoining stratiform (TL/AS) MCSs was used as initial and lateral boundary conditions for a numerical simulation of this MCS archetype. The composite atmospheric progression retained the horizontally inhomogeneous atmospheric features that commonly occur in association with TL/AS MCSs.

A realistic TL/AS MCS initiated and evolved within a simulated mesoscale environment that featured a low-level jet terminus, maximized low-level warm air advection, and elevated maximum in convective available potential energy. The lifecycle of the simulated MCS is detailed here in terms of three main stages of evolution. During the first stage an eastward moving trailing-stratiform type MCS developed and generated a surface cold pool, with convection having predominantly resided along the southeast flank of the cold pool. In the second stage, new convection re-developed north of the surface cold pool boundary within a region of low-level convergence left by the initial system. This redeveloping convection then organized into a training line with geographically fixed upstream backbuilding on the western end. Eventually the cold pool strengthened, deepened, and surged southward, resulting in the weakening and slow southward movement of the training line, which marked the third evolutionary stage. The low-level vertical wind shear profile favored kinematic lifting along the southeastern cold pool flank over the southwestern flank, potentially explaining why convection was present (absent) in the former (later) regions.