Influence of variations in low-level moisture and soil moisture on the organization of summer convective systems in the US Midwest

A primary focus of the operational forecasting community is the timing of convective initiation. Rapid changes in the structure of the Planetary Boundary Layer (PBL) during the daytime can have a significant influence on the timing of convective initiation and on the development of summer storms. In this study, we investigate connections between PBL thermodynamics, surface moisture flux from vegetation and soil moisture variability; and how these interactions impact the organization of convective systems in the Midwest using the Colorado State University Regional Atmospheric Modeling System (RAMS). For this study, we modified RAMS initialization routines to assimilate the ETA regional reanalysis data for initial and lateral boundary conditions and then configured the model to simulate transient systems centered over the Midwest for August 2000. We also used the NLDAS soil moisture data as initial condition and assimilated satellite derived leaf area index (LAI) in the experiments. Appropriate topography, soil, and sea-surface temperature were specified. Our modeling framework was designed to generate insights into the processes by which summertime convective storms form and organize in the Midwest based on a case study of August 2000. Results show a more realistic representation of the surface boundary affects the amount and spatial distribution of precipitation and improves the model-generated precipitation as compared to NCEP observations.