Quantitative simulations of dendritic growth using the phase-field method remain conditioned by the link between accurate predictions of dendritic growth dynamics and accurate morphological description of dendritic tip radii, which has restricted quantitative predictions to dilute alloys, solidifying at a relatively high solute supersaturation. For concentrated alloys, experiencing a wider scale separation between dendritic tips and solute transport in the liquid, we developed a multiscale “Dendritic Needle Network” model. By lifting the necessity to explicitly represent the solid-liquid interface, this approach enables simulating tens of thousands of individual needle-like dendritic branches interacting within grains, and among different grains. We present a first implementation of this model that incorporates convection in the liquid phase. We show that quantitative predictions comparable to phase-field can be achieved, hence opening the way to macro-scale simulations with experimental/processing relevant transport conditions, e.g. accounting for gravity-driven buoyancy and its effect on microstructure selection.