The Weather and Research Forecasting (WRF) Software Framework (WSF) supports two dynamical solvers: the Advanced Research WRF (ARW, Skamarock et al. 2005) developed by the Mesoscale and Microscale Meteorology (MMM) Division of the National Center for Atmospheric Research (NCAR), and the Nonhydrostatic Mesoscale Model (NMM – Janjic 2003) developed by the National Centers for Environmental Prediction (NCEP). WRF also offers a variety of physics packages.

Parallel runs of these two dynamic solvers are available from a variety of experiments (e.g., WRF Test Plan (Seaman et al. 2004), Spring Program (Kain et al. 2005), DTC Winter Forecast Experiment (Bernardet et al. 2005)), but the differences between these parallel runs can not be solely attributed to differences between the two dynamical cores because the dynamical solvers were not configured to use the same physical parameterizations and/or initial conditions. The Developmental Testbed Center (DTC) and the Global Systems Division (GSD) of NOAA’s Earth System Research Laboratory (ESRL) addressed the need for a controlled comparison of these two dynamical cores through intensive retrospective testing (i.e., parallel runs of the two dynamical solvers using initial and lateral boundary conditions based on the same input data, as well as the same suite of physics parameterizations).

The goal of the WRF Rapid Refresh Core Test was to determine the impact of the dynamical solvers on the forecast. With this intent, parallel runs of WRF using the two dynamical solvers were configured such that differences between the forecasts would be confined to those related to the dynamical solvers, at least within the limitations of the end-to-end system available at the time this test was conducted. This intensive testing provided much needed information for the dynamical core recommendation made by ESRL-GSD for the WRF Rapid Refresh to be run at NCEP.