Mechanisms contributing to MCS development over the southern Plains during BAMEX

An unusually strong subtropical jet prevailed over the southwest United States and southern Plains during 5–14 June 2003 in conjunction with the field phase of the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). A noteworthy aspect of this period was the wide variety of organized mesoscale convective systems (MCSs) that occurred over the southern Plains in the poleward jet-exit region of the subtropical jet. In previous studies of serial nocturnal MCS development over the central and northern Plains, it has been shown that MCSs typically occur in strongly sheared environments on the cool side of zonally oriented low-level baroclinic zones. Low-level frontogenesis, enhanced during the overnight hours by the southerly low-level jet, is important in the vertical advection and pooling of elevated moisture north of the barolinic zone. The locally enhanced moisture contributes to high elevated convective available potential energy (CAPE) values in which the eastward moving MCSs can feed upon.

The serial MCSs that occurred over the southern Plains during 5–14 June 2003, however, were embedded in a more subtropical environment with weaker deep-layer wind shear and low-level thermal gradients compared to their central and northern Plains counterpart. The aim of this presentation will be to examine and diagnose the physical and dynamical mechanisms that contributed to MCS development and maintenance in the more subtropical environment over the southern Plains on 5–14 June 2003. The findings will be compared and contrasted to environments with stronger synoptic-scale forcing typically found over the central and northern Plains during the summer months.