File:A comparison of model performance between the nested grid and Eta models (IA acomparisonofmod1094542792).pdf

Assessment of the performance of the National Meteorological Center's (NMC) new Eta numerical weather prediction model requires objective evaluation through direct comparison of model forecast output to its own analysis and to the analysis of other numerical models. The ultimate goal of the Eta Model is to provide accurate mesoscale weather forecasts through the late 1990's which are superior to those currently provided by the older NGM. To accurately evaluate the Eta Model, several model forecast output fields were compared to the NGM for a common population of extratropical cyclones over a period of five months. The separate model forecasts were also evaluated against their own analysis. Selected fields included central sea level pressure. 12h central pressure change 1000-500 mb thickness at the cyclone center, and both convective and total precipitation at the cyclone center. Results indicated a consistent negative bias in forecast central pressure values for the NGM. and a positive bias for the Eta Model. Mean forecast position errors were nearly identical for both models through 36h with the Eta forecast position errors only slightly larger at 48h. Both models exhibited a slight cold bias in 1000-500 mb thickness fields at the cyclone centers with the NGM being greater. The Eta Model tended to forecast more precipitation in general and in particular the precipitation was higher for stable precipitation.