Evaluation of Mesoscale Convective System Rainfall Predictability in the Upper Midwest Considering System Morphology

Iowa State University, Ames IA

Investigators

Abstract

Prediction of warm season convective rainfall remains a challenge, particularly for systems occurring in the absence of orographic or strong larger-scale forcing. Under a prior award, the Principal Investigator focused on improving numerical model Quantitative Precipitation Forecast (QPF) guidance for summer convection. The present research provides a continuation of this research, with a goal of improved use of mixed-physics ensemble guidance, while examining also physical processes associated with mesoscale convective system (MCS) morphology and evolution in the Upper Midwest. The Principal Investigator will explore MCS evolution and morphology, with primary emphasis on differences between systems with trailing stratiform regions and those with leading stratiform regions, by analyzing the outputs of fine grid spacing versions of the NCEP Eta and WRF (Weather Research and Forecasting) models. The use of different models and convection-related physical parameterizations will allow the following two goals to be pursued. First, careful analysis of observed MCSs and comparison with the different mixed model/mixed physics ensemble members will improve understanding of physical processes important in system evolution. Also detailed spatial and temporal investigations of the realism of the simulated MCSs will be pursued. Second, it is suggested that mixed model/mixed physics ensembles will be one of the most direct means of improving warm season mesoscale QPF. This approach will assist in improving QPF, particularly because the emphasis on different MCS morphology will reveal strengths and weaknesses within model parameterizations of physical processes important in the development and evolution of the different MCS modes. This analysis will additionally help improve understanding of the origins of diversity in model forecasts, which should assist in design of optimal mixed-physics ensembles. The researchers also will run selective cloud-resolving scale simulations for each case to which physical processes and QPF will be compared with the runs using parameterized convection. The Principal Investigator will implement new strategies for verification of high resolution models that will improve understanding about verification/evaluation of rainfall on refined spatial and temporal scales. Completion of the proposed research will improve understanding of the development and evolution of convective systems in the Midwest. In addition, the research will facilitate future advances in mesoscale meteorology by establishing the most beneficial uses of refined resolution ensemble guidance for warm season convective system forecasting.