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1. Introduction
Doppler weather radar has the capability to scan a large volume of the atmosphere at high spatial and temporal resolutions. The network of Weather Surveillance Radars-1988 Doppler (WSR-88Ds) or Next Generation Weather Radar (NEXRAD) sites provides invaluable observations for observing atmospheric conditions at high resolution across the United States (Crum and Alberty 1993). The images from radar observations are successfully used to detect severe weather and warn of thunderstorms (Burgess 2004; Mitchell et al. 1998; Vasiloff 2001; Liu et al. 2007). The use of high-resolution radar data to improve numerical weather prediction (NWP) is also active in the academic and research communities. A number of algorithms have been developed over the years to initialize numerical prediction models by assimilating the radar reflectivity and/or radial wind observations. This body of research indicates that the utilization of radar data has great potential for improving NWP forecasts (Carley 2012; Dowell et al. 2011; Hu et al. 2006; Stensrud et al. 2009; Sun 2005; Xue et al. 2000).
However, progress in using high-resolution level II data in operational NWP models has been much slower than in research models over the years (Weygandt and Benjamin 2007; Alpert and Kumar 2007). The lack of progress may be attributable to key obstacles such as 1) difficulty in transmitting relatively large volumes of radar to the operational center in real time, 2) radar data decoding software and storage requiring an excessive amount of computational resources, 3) operational high-resolution storm-scale data assimilation systems using radar observations that require huge amounts of computational resources, and 4) various radar data quality problems that can limit the application of radar data for operational use. Owing to the success of the Collaborative Radar Acquisition Field Test project (CRAFT; Droegemeier et al. 2002), the National Centers for Environmental Prediction (NCEP) have been accessing the level II data in real time from a network of 156 National Weather Service (NWS) WSR-88D radars since May 2005. The NCEP Central Operations (NCO) facility has assigned a dedicated node with 32 processors in the NCEP’s operational supercomputing environment to process level II radar data in real time. With the addition of these computational and disk storage resources, the first two obstacles were overcome. Recently, NCEP has gradually begun to gain the...