Potential vorticity streamers and their role in the development of mesoscale convective systems, part III: numerical weather simulations

In the summer of 1999, a narrow stream of potential vorticity "PV streamer" in the upper troposphere was observed to be correlated to a sequence of mesoscale convective complexes (MCCs) that produced severe weather and heavy precipitation over the central and southern plains States. Analyses of observational data presented by the authors in previous work have revealed a possible dynamical connection between the PV streamers and the intense phase of the MCC development. Because observational data (profilers, radiosondes, and ACARS) are sparse in the upper troposphere and therefore cannot properly resolve the mesoscale features of the PV streamers or the MCCs, we have began a project to thoroughly investigate using numerical simulations a selected set of these MCC-PV streamer events. Analyses of model output from Eta and RUC completed so far have revealed that the vertical resolution in the upper troposphere is not adequate to resolve the vertical structures of the PV streamers suggesting that the true connection to MCC development is not correctly portrayed. Results will be presented of ongoing sensitivity simulations using the nonhydrostatic Regional Analysis and Mesoscale System (RAMS) to test the requirements of vertical and horizontal resolutions and model physics necessary to describe the PV streamers and their connection to the MCCs. Furthermore, the pressing need for accurate precipitation forecasting by the National Weather and the private sector is the main motivation to pursue a comprehensive verification with available observational data of the precipitation forecasted by the models for several MCC cases.