| The Pennsylvania State University/National Centers for Atmospheric Research Mesoscale Model Version 5 (MM5) is employed to investigate the structure, evolution, and attendant circulations of midwestern quasi-linear mesoscale convective systems (QLCSs). For each case, the model employs the use of either three or four domains with 27-, 9-, 3-, and 1-km grid spacing, respectively.; Two cases were chosen for this study. The first case is a dynamically driven event in which the model forecast is very accurate. The kinematic and dynamic structure of the simulated system are examined in order to ascertain detailed information concerning the model's ability to initiate and maintain a QLCS some time after model initialization. Simulated reflectivity fields show an incredible amount of accuracy in representing the observations. Vertical cross-sections show the model's ability to capture the differing stages of evolution at different locations along the squall line. Horizontal cross-sections show several regions of intense updrafts and downdrafts located along the leading edge of the system. Many of the updrafts are collocated with intense centers of positive vertical vorticity. Several of these rotating updrafts attain a diameter; vertical velocity, vertical vorticity, and rotational velocity values consistent with those found in mesocyclones. Additionally, the model-forecast low-level kinematic fields create a reflectivity pattern similar to the observed line-echo-wave-pattern.; Overall, the results for the second case are not as accurate as the first. The model is never truly able to organize a system consistent with observations. The error is likely attributed to inadequate initialization of existing convection and subsequent poor surface forecasts. This suggests a limit on the usefulness of the model's forecasts given the existence of significant convection at the time of model initialization. |
