Sensitivity of WRF-RTFDDA model physics in weather forecasting applications: From synoptic scale to meso-gamma scale

The WRF-RTFDDA developed at NCAR's Research Applications Laboratory (RAL) has been used to support weather forecasting for a number of sponsors across different geographic regions. Choosing a set of physics options appropriate for the diverse scales of weather phenomena in various regions around the globe is necessary and extremely challenging at the same time. This is because each model physical scheme has its own inherit strengths and weaknesses. In addition, the numerical forecast becomes more and more sensitive to the model physics as the spatial (and temporal) scales of the weather phenomena become smaller. Due to the numerous possible combinations of physics options in mesoscale modeling systems such as WRF, it is necessary and practical to identify the major variables of interest in a given weather phenomenon, and then to select the (single or few) appropriate physics scheme(s) for best prediction of the most interesting variables. In this paper, we document our experience and challenges with WRF-RTFDDA model physics sensitivity for several weather phenomena ranging from synoptic scale to meso-gamma scale. The case studies include a) the sensitivity of planetary boundary layer/surface layer in the low-level wind forecast during a cold frontal passage in the lee of the Colorado Rockies, b) the sensitivity of cloud microphysics in the low-level wind and forecast and precipitation prediction associated with mesoscale convective systems (MCSs) in the lee of the Colorado Rockies, Midwest, and the Eastern Mediterranean, and c) the sensitivity of radiation and planetary boundary layer/surface layer schemes in the forecast of coastal stratus clouds in the Eastern Mediterranean and surface temperature under cold and stable temperature inversion conditions in the Midwest.