Enhancements to, and Recent Applications of, the ATEC Data Assimilation and Forecast System Jim Bowers 1 , Scott Swerdlin 2 , Tom Warner 2 , Yubao Liu 2 , Laurie Carson 2 , Al Bourgeois 2 , Hank Fischer 2 , David Hahn 2 , Simon Low-Nam 2 , Daran Rife 2 , Troy Sandblom 2 , Bob Sharman 2 , Rong Sheu 2 , Francois Vandenberghe 2 , and Mei Xu 2 1 U.S. Army Dugway Proving Ground, Dugway, Utah 2 National Center for Atmospheric Research, Boulder, CO ABSTRACT The U.S. Army Test and Evaluation Command (ATEC) Four-Dimensional Weather (4DWX) System includes a mesogamma-scale, model-based meteorological analysis and forecast system that has been deployed at five Army test ranges. The 4DWX modeling system employs a “nudging” (Newtonian relaxation) data assimilation procedure to incorporate a variety of standard and nonstandard observations into analyses of current conditions that are consistent with the model dynamics. These analyses typically are used to initiate forecasts every 3 h, with a typical model configuration providing 24-h forecasts for a nested grid system with a horizontal grid increment of about 1 km on the inner-most grid. This paper discusses recent applications of the 4DWX globally relocatable modeling system and describes recent enhancements to the modeling capabilities. BACKGROUND The Four-Dimensional Weather (4DWX) System (Bowers and Shantz, 1997) is a next- generation meteorological support system that was developed by the National Center for Atmospheric Research (NCAR), in collaboration with the Meteorology Division at Dugway Proving Ground (DPG), to enhance meteorological and modeling support capabilities at the major Army test ranges. Major 4DWX components include a common data archival/retrieval system for both internal and external meteorological data sources, a high-resolution mesoscale meteorological model, a variety of user-configurable two- and three-dimensional displays of observational and model data, and linked range applications models (dispersion, noise propagation, etc.). The 4DWX mesoscale model, the Pennsylvania State University/NCAR Mesoscale Model Version 5 (MM5) (Grell et al., 1994), is now in operational use at five Army test centers: DPG, Dugway, Utah; Aberdeen Test Center (ATC), Aberdeen Proving Ground, Maryland; Cold Regions Test Center (CRTC), Fort Greeley, Alaska; White Sands Missile Range, New Mexico; and Yuma Proving Ground, Arizona. As discussed by Bowers et al. (2002), 4DWX uses MM5 in a real-time four-dimensional data assimilation (FDDA) mode in which Newtonian relaxation is used to nudge the model towards the observations (e.g., see Seaman et al., 1995). These dynamically consisted analyses typically are used to initialize 24-h forecasts every 3 h.