Towards High-Resolution NMM-B Nature Run Weather Forecasts for Hurricane OSSEs

In Observing System Simulation Experiments (OSSEs), the impact of proposed observing systems assimilated on to a state-of-the-art weather forecast model is evaluated using a nature run, which is a relatively long-duration, high resolution forecast simulation. In this work, we describe our experience generating a regional nature run for our hurricane OSSEs. Supported by NOAA's High Impact Weather Prediction Project's (HIWPP), HRD/AOML with its partners at EMC/NCEP, are working on the transition of HWRF to the NOAA Environmental Modeling System (NEMS) framework. We chose the experimental Non-hydrostatic Multiscale Model on the B-Grid (NMM-B) within the NEMS framework as the forecast model for this nature run. In evaluating the NMM-B model output for hurricane application, several pertinent questions are addressed. We start by evaluating the performance of NMM-B as a hurricane forecast model and compare model outputs using thoroughly-researched retrospective hurricane cases. In doing so, we evaluate various domain configurations in the NMM-B model. These different configurations, in turn, help us answer several questions. For one, we assess the benefit of using a single regional scale domain running at a uniform-3km resolution versus the pragmatic operational approach which uses a relatively coarse-resolution large-scale domain supplemented with higher resolution, storm-following nested domains at 3km resolution. This helps us understand how high of a resolution is required at the large scale for a specified level of forecast accuracy. Furthermore, it also helps us determine the additional benefit derived from using 2-way nesting that feeds data back from the mesoscale to the synoptic scale.