Mesoscale Weather Prediction with the RUC Hybrid Isentropic–Terrain-Following Coordinate Model

A mesoscale atmospheric forecast model configured in a hybrid isentropic-sigma vertical coordinate and used in the NOAA Rapid Update Cycle (RUC) for operational numerical guidance is presented. The RUC model is the only quasi-isentropic forecast model running operationally in the world and is distinguished from other hybrid isentropic models by its application at fairly high horizontal resolution (10-20 km) and a generalized vertical coordinate formulation that allows model levels to remain continuous and yet be purely isentropic well into the middle and even lower troposphere.