One of the primary driving forces for the selection of the Mississippi River basin as a focus for GCIP study was the presence of a wide array of meteorological and hydrological data sources in the region. However, the disparate sources and formats makes it difficult to take full advantage of these data. In an effort to alleviate these problems UCAR/JOSS developed a number of composite data sets covering various time periods and locations within the GCIP domain. These composites include surface meteorology (hourly), precipitation (15 minute, hourly, and daily), upper air, fluxes, and radiation. One of the GCIP data sets that includes each of these various types of composites is the Near Surface Observation Data Set (NESOB) which includes a warm season data set during 1996 and an annual data set covering April 1997 to March 1998 over an area centered on the ARM Southern Great Plains site. This poster will summarize the composite data sets that have been developed by UCAR/JOSS and examine the issues involved in the development of these composite data sets including data acquisition, format conversion, and quality control.