Effect of shallow convection parametrization on cloud resolving NWP forecasts over the Eastern Mediterranean

Abstract

Numerical Weather Prediction (NWP) models with coarser resolution than ~4 km use convection parametrization to describe both deep and shallow convection. Convection permitting models with grid spacing below ~4 km usually describe deep convection on grid scale, but still parametrize the shallow convection, being sub-grid scale process. Many of these parametrizations are based on the mass-flux approach. The artificial combination of resolved and parametrized convection might deteriorate the model forecast skill, particularly precipitation. In this study, we are using the COSMO 2.5 km resolution limited area NWP model over the eastern Mediterranean region to analyze the effect of the mass-flux shallow convection parametrization (SCP) on the forecasts skill. We show that SCP entrainment rate, as well as restrictions on the shallow convection development height and maximum updraft speed, have a crucial effect on the forecasts of precipitation, temperature and moisture. Physically motivated tuning of these parameters can improve the model forecasts significantly. Finally, we estimate the climatic zones and seasons where SCP is expected to be particularly important for NWP.