Explicit forecasting of deep convection with the operational convection-resolving model COSMO-DE A. Seifert and M. Baldauf Deutscher Wetterdienst, Kaiserleistr. 42, 63067 Offenbach, Germany Since April 2007 the operational NWP system of the Deutscher Wetterdienst (DWD) has been extended to the convection-resolving scale by the introduction of the 2.8 km grid-spacing limited-area model COSMO-DE (formerly known as the LMK project). The new high-resolution model COSMO-DE aims towards the explicit forecasting of severe weather phenomena on the meso-gamma scale, for example severe weather events related to deep moist convection or interactions of the flow with topography like strong orographic precipitation or downslope windstorms. We will present several case studies of severe deep convection associated with strong synoptic-scale forcing where COSMO-DE was able to successfully forecast the development of supercells, e.g. on 13th May 2007 when two tornados were observed in the area of Aachen. To detect supercells in the model forecasts the supercell detection index (SDI) of Wicker et al. (2005) has been implemented in the COSMO model as a new diagnostic output variable. The SDI uses a correlation of vertical vorticity and updraft velocity within a control volume as a measure of 'supercellness' of the simulated convective storms. Using this model diagnostic it is shown that COSMO-DE is able to simulate, and maybe even predict, long-lived severe supercell storms. In the second part of the presentation an evaluation of the diurnal cycle of deep convection in COSMO-DE forecasts will be discussed and it will be shown that the currently operational version of COSMO-DE has some deficiencies in forecasting small scale convection associated with the diurnal mode. These problems are most likely due to problems in the COSMO boundary layer scheme and some sensitivity studies are shown which support this hypotheses.