A diagnostic study of a summer convective precipitation event in the Czech Republic using a nonhydrostatic NWP model

Forecasting, locally, heavy convective precipitation events has been an important topic of investigation for a few decades. It has been recognized that nonhydrostatic models are able to simulate the dynamics of organized convective systems with spatial resolutions of 1 km and less, provided that adequate triggering is entered in the model. Apart from experimental model runs, there are also diagnostic case studies of convective events that employ such models and compare the results with radar data, for example. Nevertheless, the purely deterministic prediction of severe convective systems and the corresponding quantitative precipitation forecast (QPF) is far from being resolved. arch project, focused on case studies of severe convective events in the region of the Czech Republic (CR), has been running since 2000. Data from this study have been used to adapt the nonhydrostatic numerical weather prediction (NWP) Local Model of the German Weather Service (LM DWD) to use a 2.8-km horizontal resolution Small Local Model (SLM) for forecasting and/or warning of severe convection events. The results of several model applications are summarized and discussed. storical convective event from July 22 to 23, 1998, which caused an extreme precipitation amount and a flash flood over the NE part of the CR, was analyzed with several model runs. The model runs differed in the design of the experiment (starting time of SLM integration, convective parameterization ON/OFF, modification of model orography, etc.). The results of the SLM integration indicate that the inclusion of the convective parameterization smoothes precipitation fields, which is not realistic. The structure of precipitation fields, obtained by the SLM with convective parameterization switched OFF, better corresponds to the spatial structure of radar-derived precipitation. The resulting precipitation depends on the start time of the SLM integration. The results show that the accumulated precipitation does not differ too much, provided the SLM starts its integration at least 6 h before the studied event. The fact that the SLM produces large precipitation in contrast to the routine NWP and that the area precipitation pattern corresponds to the radar precipitation is promising.