Upscale Convective Growth of an Orogenic Supercell into a Mesoscale Convective System in Argentina, South America

The environmental and internal storm dynamics that govern upscale convective growth of discrete deep moist convection into organized mesoscale convective systems (MCSs) are still not fully understood. This is especially the case for upscale convective growth of orogenic deep moist convection. Satellite and ground-based radar studies have demonstrated that upscale convective growth near the complex terrain of the Sierras de Córdoba, Argentina, South America, is common and tends to occur close to the terrain and more rapidly than in the Central USA. Here we examine the severe convective event of 29 November 2017 near Córdoba, in which an orogenic supercell transitions into a bowing MCS over a relatively short time span of two to three hours. Owing to the lack of observations, high-resolution Weather Research and Forecasting (WRF) model simulations are used to analyze the processes that aided in this rapid upscale convective growth. Results indicate that a 333-m grid spacing control simulation accurately reproduces the evolution of convection initiation stage through supercell stage and eventual upscale convective growth of the event. Enhanced antistreamwise horizontal vorticity along the eastern edge of the highest terrain appears to aid in the formation of a dominant left-moving supercell. Shortly thereafter, strong downdrafts along and behind the rear flank gust front result in a rapid upscale transition to a bowing MCS. Sensitivity experiments in which the height of the Sierras de Córdoba are artificially raised or lowered are conducted to examine the effects terrain height have on the upscale convective growth process. All terrain height experiments result in supercell formation and eventual transition to a bowing MCS; however, the artificially higher terrain height experiments show: earlier convection initiation, stronger isallobaric backing of low-level winds, stronger cold pools, greater terrain blocking of cold pools, and greater rainfall accumulation. The earlier convection initiation is due to quicker removal of ambient convective inhibition. The greater isallobaric backing of low-level winds increases upslope flow, which locally enhances low-level antistreamwise horizontal vorticity, allowing for a more sustained and longer track left-moving supercell as compared with the lower terrain experiments (Fig. 1). Further implications of the effects of complex terrain on environmental (both thermodynamic and dynamic) and storm-scale processes related to upscale convective growth will be discussed.