| The Pennsylvania State University/National Centers for Atmospheric Research Mesoscale Model Version 5 (MM5) is employed to investigate the structure, evolution, and circulation of midwestern linear mesoscale convective systems (MCSs) during the cool and/or transitional seasons. The model employs three domains with 27-, 9-, and 3-km grid spacing, respectively. Input to the model is kept at a minimum to evaluate the utility of the MM5 model to an operational forecaster at a National Weather Service Forecast Office.; A “standard” physical package was selected after running sensitivity tests. Two cases were chosen for this study. The first case is a classic transitional season event in which the model predicted very well. The kinematic and dynamic structure of the simulated system, however, provided very detailed information as to how the model maintained a linear MCS some time after model initialization. The low-level simulated reflectivity fields show incredible similarity to the observations, and cross-sectional views show the detailed evolution occurring at different locations of the bowing segment of the squall line. Plan views from low- and mid-levels show the vertical structure of the dynamic interaction between the mass and momentum fields, which is further verified with selected cross sections. The low-level winds are also shown to create a reflectivity pattern similar to a line-echo-wave-pattern.; The second case was not as well forecast as the first. This suggests a limit on the usefulness of the model's forecasts. The surface forecasts degrade over time. The MM5 model creates some linear, simulated reflectivity patterns, but are not as organized as observations for this event. However, it is encouraging to note the degree of organization, that the model attempts to develop given the success of the previous case. |
